Hydrogen an Overview

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Hydrogen An overview

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Articles

Overview 1 Hydrogen 1 Antihydrogen 18 Hydrogen atom 20 Hydrogen-like atom 26 Hydrogen spectral series 29 Liquid hydrogen 34 Solid hydrogen 38 Metallic hydrogen 39 Nascent hydrogen 43

Isotopes 45 Isotopes of hydrogen 45 Deuterium 49 Tritium 59 Hydrogen-4 69 Hydrogen-5 70 Spin isomers of hydrogen 71

Reactions 74 Bosch reaction 74 Hydrogen cycle 75 Hydrogenation 76 Dehydrogenation 84 Transfer hydrogenation 85 Hydrogenolysis 89 Hydron 90 Sabatier reaction 91

Risks 93 Hydrogen damage 93 Hydrogen embrittlement 96 Hydrogen leak testing 99 Hydrogen safety 100 Fuel 103 Timeline of hydrogen technologies 103 Biohydrogen 107 Hydrogen production 113 Hydrogen infrastructure 118 Hydrogen line 119 Hydrogen purity 124 References Article Sources and Contributors 125 Image Sources, Licenses and Contributors 128 Article Licenses License 130 1

Overview

Hydrogen

Appearance

Colorless gas with purple glow in its plasma state

Spectral lines of Hydrogen

General properties

Name, symbol, number hydrogen, H, 1

[1] Pronunciation /ˈhaɪdrɵdʒɪn/ HYE-dro-jin

Element category nonmetal

Group, period, block 1, 1, s

−1 Standard atomic weight 1.00794(7) g·mol

Electron configuration 1s1

Electrons per shell 1 (Image)

Physical properties

Color colorless

Phase gas

Density (0 °C, 101.325 kPa) 0.08988 g/L

[2] −3 Liquid density at m.p. 0.07 (0.0763 solid) g·cm

Melting point 14.01 K,-259.14 °C,-434.45 °F

Boiling point 20.28 K,-252.87 °C,-423.17 °F

Triple point 13.8033 K (-259°C), 7.042 kPa

Critical point 32.97 K, 1.293 MPa

Heat of fusion (H ) 0.117 kJ·mol−1 2

Heat of vaporization (H ) 0.904 kJ·mol−1 2

Specific heat capacity (25 °C) (H ) 28.836 J·mol−1·K−1 2 Vapor pressure Hydrogen 2

P/Pa 1 10 100 1 k 10 k 100 k

at T/K 15 20

Atomic properties

Oxidation states 1, -1 (amphoteric oxide)

Electronegativity 2.20 (Pauling scale)

Ionization energies 1st: 1312.0 kJ·mol−1

Covalent radius 31±5 pm

Van der Waals radius 120 pm

Miscellanea

Crystal structure hexagonal

[3] Magnetic ordering diamagnetic

Thermal conductivity (300 K) 0.1805 W·m−1·K−1

Speed of sound (gas, 27 °C) 1310 m/s

CAS registry number 1333-74-0

Most stable isotopes

Main article: Isotopes of hydrogen

iso NA half-life DM DE (MeV) DP

1H 99.985% 1H is stable with 0 neutron

2H 0.015% 2H is stable with 1 neutron

3H trace 12.32 y β− 0.01861 3He

[4] Hydrogen ( /ˈhaɪdrɵdʒɪn/ HYE-dro-jin) is the chemical element with atomic number 1. It is represented by the symbol H. With an average atomic weight of 1.00794 u (1.007825 u for Hydrogen-1), hydrogen is the lightest and most abundant chemical element, constituting roughly 75 % of the Universe's elemental mass.[5] Stars in the main sequence are mainly composed of hydrogen in its plasma state. Naturally occurring elemental hydrogen is relatively rare on Earth. The most common isotope of hydrogen is protium (name rarely used, symbol 1H) with a single proton and no neutrons. In ionic compounds it can take a negative charge (an anion known as a hydride and written as H−), or as a positively charged species H+. The latter cation is written as though composed of a bare proton, but in reality, hydrogen cations in ionic compounds always occur as more complex species. Hydrogen forms compounds with most elements and is present in water and most organic compounds. It plays a particularly important role in acid-base chemistry with many reactions exchanging protons between soluble molecules. As the simplest atom known, the hydrogen atom has been of theoretical use. For example, as the only neutral atom with an analytic solution to the Schrödinger equation, the study of the energetics and bonding of the hydrogen atom played a key role in the development of quantum mechanics. Hydrogen gas (now known to be H ) was first artificially produced in the early 16th century, via the mixing of 2 metals with strong acids. In 1766–81, Henry Cavendish was the first to recognize that hydrogen gas was a discrete substance,[6] and that it produces water when burned, a property which later gave it its name, which in Greek means Hydrogen 3

"water-former." At standard temperature and pressure, hydrogen is a colorless, odorless, nonmetallic, tasteless, highly combustible diatomic gas with the molecular formula H . 2 Industrial production is mainly from the steam reforming of natural gas, and less often from more energy-intensive hydrogen production methods like the electrolysis of water.[7] Most hydrogen is employed near its production site, with the two largest uses being fossil fuel processing (e.g., hydrocracking) and ammonia production, mostly for the fertilizer market. Hydrogen is a concern in metallurgy as it can embrittle many metals,[8] complicating the design of pipelines and storage tanks.[9]

Properties

Combustion

Hydrogen gas (dihydrogen or molecular hydrogen)[10] is highly flammable and will burn in air at a very wide range of concentrations between 4% and 75% by volume.[11] The enthalpy of combustion for hydrogen is −286 kJ/mol:[12] 2 H (g) + O (g) → 2 H O(l) + 572 kJ (286 kJ/mol)[13] 2 2 2 Hydrogen gas forms explosive mixtures with air in the concentration range 4–74% (volume per cent of hydrogen in air) and with chlorine in the range 5–95%. The mixtures spontaneously detonate by spark, heat or sunlight. The hydrogen autoignition temperature, the temperature of spontaneous ignition in air, is 500 °C (932 °F).[14] Pure hydrogen-oxygen flames emit ultraviolet light The Space Shuttle Main Engine and are nearly invisible to the naked eye, as illustrated by the faint plume of the burns hydrogen with oxygen, Space Shuttle main engine compared to the highly visible plume of a Space producing a nearly invisible flame at full thrust. Shuttle Solid Rocket Booster. The detection of a burning hydrogen leak may require a flame detector; such leaks can be very dangerous. The destruction of the Hindenburg airship was an infamous example of hydrogen combustion; the cause is debated, but the visible flames were the result of combustible materials in the ship's skin.[15] Because hydrogen is buoyant in air, hydrogen flames tend to ascend rapidly and cause less damage than hydrocarbon fires. Two-thirds of the Hindenburg passengers survived the fire, and many deaths were instead the result of falls or burning diesel fuel.[16]

H reacts with every oxidizing element. Hydrogen can react spontaneously and violently at room temperature with 2 chlorine and fluorine to form the corresponding hydrogen halides, hydrogen chloride and hydrogen fluoride, which are also potentially dangerous acids.[17] Hydrogen 4

Electron energy levels

The ground state energy level of the electron in a hydrogen atom is −13.6 eV, which is equivalent to an ultraviolet photon of roughly 92 nm wavelength.[18] The energy levels of hydrogen can be calculated fairly accurately using the Bohr model of the atom, which conceptualizes the electron as "orbiting" the proton in analogy to the Earth's orbit of the sun. However, the electromagnetic force attracts electrons and protons to one another, while planets and celestial objects are attracted to each other by gravity. Because of the discretization of angular momentum postulated in early quantum mechanics by Bohr, the electron in the Bohr model can only occupy certain allowed distances from the proton, Depiction of a hydrogen atom showing the and therefore only certain allowed energies.[19] diameter as about twice the Bohr model radius (image not to scale). A more accurate description of the hydrogen atom comes from a purely quantum mechanical treatment that uses the Schrödinger equation or the equivalent Feynman path integral formulation to calculate the probability density of the electron around the proton.[20]

Elemental molecular forms

There exist two different spin isomers of hydrogen diatomic molecules that differ by the relative spin of their nuclei.[21] In the orthohydrogen form, the spins of the two protons are parallel and form a triplet state with a molecular spin quantum number of 1 (½+½); in the parahydrogen form the spins are antiparallel and form a singlet with a molecular spin quantum number of 0 (½-½). At standard temperature and pressure, hydrogen gas contains about 25% of the para form and 75% of the ortho form, also known as the "normal form".[22] The equilibrium ratio of orthohydrogen to parahydrogen depends on temperature, but because the ortho form is an excited state and has a higher energy than the para form, it is unstable and cannot be purified. At very low temperatures, the equilibrium state is composed almost exclusively of the para form. The liquid and gas phase thermal properties of pure parahydrogen differ significantly from those of the normal form because of differences in rotational heat capacities, as discussed more fully in Spin isomers of hydrogen.[23] The ortho/para First tracks observed in liquid hydrogen bubble distinction also occurs in other hydrogen-containing molecules or chamber at the Bevatron functional groups, such as water and methylene, but is of little significance for their thermal properties.[24]

The uncatalyzed interconversion between para and ortho H increases with increasing temperature; thus rapidly 2 condensed H contains large quantities of the high-energy ortho form that converts to the para form very slowly.[25] 2 The ortho/para ratio in condensed H is an important consideration in the preparation and storage of liquid hydrogen: 2 the conversion from ortho to para is exothermic and produces enough heat to evaporate some of the hydrogen liquid, leading to loss of liquefied material. Catalysts for the ortho-para interconversion, such as ferric oxide, activated carbon, platinized asbestos, rare earth metals, uranium compounds, chromic oxide, or some nickel[26] compounds, are used during hydrogen cooling.[27] Hydrogen 5

A molecular form called protonated molecular hydrogen, or H , is found in the interstellar medium (ISM), where it is generated by ionization of molecular hydrogen from cosmic rays. It has also been observed in the upper atmosphere of the planet Jupiter. This molecule is relatively stable in the environment of outer space due to the low temperature and density. H is one of the most abundant ions in the Universe, and it plays a notable role in the chemistry of the interstellar medium.[28] Neutral triatomic hydrogen H can only exist in an excited from and is 3 unstable.[29] Compounds

Covalent and organic compounds While H is not very reactive under standard conditions, it does form compounds with most elements. Millions of 2 hydrocarbons are known, but they are not formed by the direct reaction of elementary hydrogen and carbon. Hydrogen can form compounds with elements that are more electronegative, such as halogens (e.g., F, Cl, Br, I); in these compounds hydrogen takes on a partial positive charge.[30] When bonded to fluorine, oxygen, or nitrogen, hydrogen can participate in a form of strong noncovalent bonding called hydrogen bonding, which is critical to the stability of many biological molecules.[31] [32] Hydrogen also forms compounds with less electronegative elements, such as the metals and metalloids, in which it takes on a partial negative charge. These compounds are often known as hydrides.[33] Hydrogen forms a vast array of compounds with carbon. Because of their general association with living things, these compounds came to be called organic compounds;[34] the study of their properties is known as organic chemistry[35] and their study in the context of living organisms is known as biochemistry.[36] By some definitions, "organic" compounds are only required to contain carbon. However, most of them also contain hydrogen, and because it is the carbon-hydrogen bond which gives this class of compounds most of its particular chemical characteristics, carbon-hydrogen bonds are required in some definitions of the word "organic" in chemistry.[34] In inorganic chemistry, hydrides can also serve as bridging ligands that link two metal centers in a coordination complex. This function is particularly common in group 13 elements, especially in boranes (boron hydrides) and aluminium complexes, as well as in clustered carboranes.[37]

Hydrides Compounds of hydrogen are often called hydrides, a term that is used fairly loosely. The term "hydride" suggests that the H atom has acquired a negative or anionic character, denoted H−, and is used when hydrogen forms a compound with a more electropositive element. The existence of the hydride anion, suggested by Gilbert N. Lewis in 1916 for group I and II salt-like hydrides, was demonstrated by Moers in 1920 with the electrolysis of molten lithium hydride (LiH), that produced a stoichiometric quantity of hydrogen at the anode.[38] For hydrides other than group I and II metals, the term is quite misleading, considering the low electronegativity of hydrogen. An exception in group II hydrides is BeH , which is polymeric. In lithium aluminium hydride, the AlH anion carries hydridic centers firmly 2 attached to the Al(III). Although hydrides can be formed with almost all main-group elements, the number and combination of possible compounds varies widely; for example, there are over 100 binary borane hydrides known, but only one binary aluminium hydride.[39] Binary indium hydride has not yet been identified, although larger complexes exist.[40] Hydrogen 6

Protons and acids Oxidation of hydrogen, in the sense of removing its electron, formally gives H+, containing no electrons and a nucleus which is usually composed of one proton. That is why H+ is often called a proton. This species is central to discussion of acids. Under the Bronsted-Lowry theory, acids are proton donors, while bases are proton acceptors. A bare proton, H+, cannot exist in solution or in ionic crystals, because of its unstoppable attraction to other atoms or molecules with electrons. Except at the high temperatures associated with plasmas, such protons cannot be removed from the electron clouds of atoms and molecules, and will remain attached to them. However, the term 'proton' is sometimes used loosely and metaphorically to refer to positively charged or cationic hydrogen attached to other species in this fashion, and as such is denoted "H+" without any implication that any single protons exist freely as a species. To avoid the implication of the naked "solvated proton" in solution, acidic aqueous solutions are sometimes considered to contain a less unlikely fictitious species, termed the "hydronium ion" (H O+). However, even in this 3 case, such solvated hydrogen cations are thought more realistically physically to be organized into clusters that form species closer to H O .[41] Other oxonium ions are found when water is in solution with other solvents.[42] 9 Although exotic on earth, one of the most common ions in the universe is the H ion, known as protonated molecular hydrogen or the triatomic hydrogen cation.[43]

Isotopes

Hydrogen has three naturally occurring isotopes, denoted 1H, 2H and 3H. Other, highly unstable nuclei (4H to 7H) have been synthesized in the laboratory but not observed in nature.[44] [45] • 1H is the most common hydrogen isotope with an abundance of Hydrogen discharge (spectrum) tube more than 99.98%. Because the nucleus of this isotope consists of only a single proton, it is given the descriptive but rarely used formal name protium.[46] • 2H, the other stable hydrogen isotope, is known as deuterium and contains one proton and one neutron in its nucleus. Essentially all deuterium in the universe is thought to have been produced at the time of the Big Bang, and has endured since that time. Deuterium is Deuterium discharge (spectrum) tube not radioactive, and does not represent a significant toxicity hazard. Water enriched in molecules that include deuterium instead of normal hydrogen is called heavy water. Deuterium and its compounds are used as a non-radioactive label in chemical experiments and in solvents for 1H-NMR spectroscopy.[47] Heavy water is used as a neutron moderator and coolant for nuclear reactors. Deuterium is also a potential fuel for commercial nuclear fusion.[48] • 3H is known as tritium and contains one proton and two neutrons in its nucleus. It is radioactive, decaying into helium-3 through beta decay with a half-life of 12.32 years.[37] Small amounts of tritium occur naturally because of the interaction of cosmic rays with atmospheric gases; tritium has also been released during nuclear weapons tests.[49] It is used in nuclear fusion reactions,[50] as a Hydrogen 7

tracer in isotope geochemistry,[51] and specialized in self-powered lighting devices.[52] Tritium has also been used in chemical and biological labeling experiments as a radiolabel.[53] Hydrogen is the only element that has different names for its isotopes in common use today. (During the early study of radioactivity, various heavy radioactive isotopes were given names, but such names are no longer used). The symbols D and T (instead of 2H and 3H) are sometimes used for deuterium and tritium, but the corresponding symbol P is already in use for phosphorus and thus is not available for protium.[54] In its nomenclatural guidelines, the International Union of Pure and Applied Chemistry allows any of D, T, 2H, and 3H to be used, 2 3 [55] although H and H are preferred. Protium, the most common isotope of hydrogen, has one proton and one electron. Unique among all stable isotopes, it has no neutrons (see diproton for discussion of why others do not exist).

History

Discovery and use Hydrogen gas, H , was first artificially produced and formally described by T. Von Hohenheim (also known as 2 Paracelsus, 1493–1541) via the mixing of metals with strong acids.[56] He was unaware that the flammable gas produced by this chemical reaction was a new chemical element. In 1671, Robert Boyle rediscovered and described the reaction between iron filings and dilute acids, which results in the production of hydrogen gas.[57] [58] In 1766, Henry Cavendish was the first to recognize hydrogen gas as a discrete substance, by identifying the gas from a metal-acid reaction as "flammable air" and further finding in 1781 that the gas produces water when burned. He is usually given credit for its discovery as an element.[59] [60] In 1783, Antoine Lavoisier gave the element the name hydrogen (from the Greek ὕδρω hydro meaning water and γενῆς genes meaning creator)[61] when he and Laplace reproduced Cavendish's finding that water is produced when hydrogen is burned.[60] Hydrogen was liquefied for the first time by James Dewar in 1898 by using regenerative cooling and his invention, the vacuum flask.[60] He produced solid hydrogen the next year.[60] Deuterium was discovered in December 1931 by Harold Urey, and tritium was prepared in 1934 by Ernest Rutherford, Mark Oliphant, and Paul Harteck.[59] Heavy water, which consists of deuterium in the place of regular hydrogen, was discovered by Urey's group in 1932.[60] François Isaac de Rivaz built the first internal combustion engine powered by a mixture of hydrogen and oxygen in 1806. Edward Daniel Clarke invented the hydrogen gas blowpipe in 1819. The Döbereiner's lamp and limelight were invented in 1823.[60] The first hydrogen-filled balloon was invented by Jacques Charles in 1783.[60] Hydrogen provided the lift for the first reliable form of air-travel following the 1852 invention of the first hydrogen-lifted airship by Henri Giffard.[60] German count Ferdinand von Zeppelin promoted the idea of rigid airships lifted by hydrogen that later were called Zeppelins; the first of which had its maiden flight in 1900.[60] Regularly scheduled flights started in 1910 and by the outbreak of World War I in August 1914, they had carried 35,000 passengers without a serious incident. Hydrogen-lifted airships were used as observation platforms and bombers during the war. The first non-stop transatlantic crossing was made by the British airship R34 in 1919. Regular passenger service resumed in the 1920s and the discovery of helium reserves in the United States promised increased safety, but the U.S. government refused to sell the gas for this purpose. Therefore, H was used in the Hindenburg airship, which 2 Hydrogen 8

was destroyed in a midair fire over New Jersey on May 6, 1937.[60] The incident was broadcast live on radio and filmed. Ignition of leaking hydrogen is widely assumed to be the cause, but later investigations pointed to the ignition of the aluminized fabric coating by static electricity. But the damage to hydrogen's reputation as a lifting gas was already done. In the same year the first hydrogen-cooled turbogenerator went into service with gaseous hydrogen as a coolant in the rotor and the stator in 1937 at Dayton, Ohio, by the Dayton Power & Light Co,[62] because of the thermal conductivity of hydrogen gas this is the most common type in its field today. The nickel hydrogen battery was used for the first time in 1977 aboard the U.S. Navy's Navigation technology satellite-2 (NTS-2).[63] For example, the ISS,[64] Mars Odyssey[65] and the Mars Global Surveyor[66] are equipped with nickel-hydrogen batteries. The Hubble Space Telescope, at the time its original batteries were finally changed in May 2009, more than 19 years after launch, led with the highest number of charge/discharge cycles.

Role in quantum theory

Because of its relatively simple atomic structure, consisting only of a proton and an electron, the hydrogen atom,

together with the spectrum of light Hydrogen emission spectrum lines in the visible range. These are the four visible lines of produced from it or absorbed by it, has the Balmer series been central to the development of the theory of atomic structure.[67] Furthermore, the corresponding simplicity of the hydrogen molecule and the corresponding cation H + allowed fuller understanding of the nature of the chemical bond, which followed shortly 2 after the quantum mechanical treatment of the hydrogen atom had been developed in the mid-1920s.

One of the first quantum effects to be explicitly noticed (but not understood at the time) was a Maxwell observation involving hydrogen, half a century before full quantum mechanical theory arrived. Maxwell observed that the specific heat capacity of H unaccountably departs from that of a diatomic gas below room temperature and begins to 2 increasingly resemble that of a monatomic gas at cryogenic temperatures. According to quantum theory, this behavior arises from the spacing of the (quantized) rotational energy levels, which are particularly wide-spaced in H 2 because of its low mass. These widely spaced levels inhibit equal partition of heat energy into rotational motion in hydrogen at low temperatures. Diatomic gases composed of heavier atoms do not have such widely spaced levels and do not exhibit the same effect.[68]

Natural occurrence Hydrogen 9

Hydrogen is the most abundant element in the universe, making up 75% of normal matter by mass and over 90% by number of atoms.[69] This element is found in great abundance in stars and gas giant planets. Molecular clouds of H are associated with star formation. Hydrogen 2 plays a vital role in powering stars through proton-proton reaction and CNO cycle nuclear fusion.[70]

Throughout the universe, hydrogen is mostly found in the atomic and plasma states whose properties are quite different from molecular hydrogen. As a plasma, hydrogen's electron and proton are not bound together, resulting in very high electrical conductivity and high emissivity (producing the light from the sun and other stars). The charged particles are highly influenced by magnetic and electric fields. NGC 604, a giant region of ionized hydrogen in For example, in the solar wind they interact with the Earth's the Triangulum Galaxy magnetosphere giving rise to Birkeland currents and the aurora. Hydrogen is found in the neutral atomic state in the Interstellar medium. The large amount of neutral hydrogen found in the damped Lyman-alpha systems is thought to dominate the cosmological baryonic density of the Universe up to redshift z=4.[71]

Under ordinary conditions on Earth, elemental hydrogen exists as the diatomic gas, H (for data see table). However, 2 hydrogen gas is very rare in the Earth's atmosphere (1 ppm by volume) because of its light weight, which enables it to escape from Earth's gravity more easily than heavier gases. However, hydrogen is the third most abundant element on the Earth's surface.[72] Most of the Earth's hydrogen is in the form of chemical compounds such as hydrocarbons and water.[37] Hydrogen gas is produced by some bacteria and algae and is a natural component of flatus, as is methane, itself a hydrogen source of increasing importance.[73]

Production H is produced in chemistry and biology laboratories, often as a by-product of other reactions; in industry for the 2 hydrogenation of unsaturated substrates; and in nature as a means of expelling reducing equivalents in biochemical reactions.

Laboratory In the laboratory, H is usually prepared by the reaction of acids on metals such as zinc with Kipp's apparatus. 2 Zn + 2 H+ → Zn2+ + H 2 Aluminium can also produce H upon treatment with bases: 2 2 Al + 6 H O + 2 OH− → 2 Al(OH) + 3 H 2 2 The electrolysis of water is a simple method of producing hydrogen. A low voltage current is run through the water, and gaseous oxygen forms at the anode while gaseous hydrogen forms at the cathode. Typically the cathode is made from platinum or another inert metal when producing hydrogen for storage. If, however, the gas is to be burnt on site, oxygen is desirable to assist the combustion, and so both electrodes would be made from inert metals. (Iron, for instance, would oxidize, and thus decrease the amount of oxygen given off.) The theoretical maximum efficiency (electricity used vs. energetic value of hydrogen produced) is between 80–94%.[74] 2 H O(aq) → 2 H (g) + O (g) 2 2 2 In 2007, it was discovered that an alloy of aluminium and gallium in pellet form added to water could be used to generate hydrogen. The process also creates alumina, but the expensive gallium, which prevents the formation of an oxide skin on the pellets, can be re-used. This has important potential implications for a hydrogen economy, as Hydrogen 10

hydrogen can be produced on-site and does not need to be transported.[75]

Industrial Hydrogen can be prepared in several different ways, but economically the most important processes involve removal of hydrogen from hydrocarbons. Commercial bulk hydrogen is usually produced by the steam reforming of natural gas.[76] At high temperatures (1000–1400 K, 700–1100 °C or 1300–2000 °F), steam (water vapor) reacts with methane to yield carbon monoxide and H . 2 CH + H O → CO + 3 H 4 2 2 This reaction is favored at low pressures but is nonetheless conducted at high pressures (2.0 MPa, 20 atm or 600 inHg). This is because high-pressure H is the most marketable product and Pressure Swing Adsorption (PSA) 2 purification systems work better at higher pressures. The product mixture is known as "synthesis gas" because it is often used directly for the production of methanol and related compounds. Hydrocarbons other than methane can be used to produce synthesis gas with varying product ratios. One of the many complications to this highly optimized technology is the formation of coke or carbon: CH → C + 2 H 4 2 Consequently, steam reforming typically employs an excess of H O. Additional hydrogen can be recovered from the 2 steam by use of carbon monoxide through the water gas shift reaction, especially with an iron oxide catalyst. This reaction is also a common industrial source of carbon dioxide:[76] CO + H O → CO + H 2 2 2 Other important methods for H production include partial oxidation of hydrocarbons:[77] 2 2 CH + O → 2 CO + 4 H 4 2 2 and the coal reaction, which can serve as a prelude to the shift reaction above:[76] C + H O → CO + H 2 2 Hydrogen is sometimes produced and consumed in the same industrial process, without being separated. In the Haber process for the production of ammonia, hydrogen is generated from natural gas.[78] Electrolysis of brine to yield chlorine also produces hydrogen as a co-product.[79]

Thermochemical There are more than 200 thermochemical cycles which can be used for water splitting, around a dozen of these cycles such as the iron oxide cycle, cerium(IV) oxide-cerium(III) oxide cycle, zinc zinc-oxide cycle, sulfur-iodine cycle, copper-chlorine cycle and hybrid sulfur cycle are under research and in testing phase to produce hydrogen and oxygen from water and heat without using electricity.[80] A number of laboratories (including in France, Germany, Greece, Japan, and the USA) are developing thermochemical methods to produce hydrogen from solar energy and water.[81] Hydrogen 11

Anaerobic corrosion Under anaerobic conditions, iron and steel alloys are slowly oxidized by the protons of water concomitantly reduced in molecular hydrogen (H ). The anaerobic corrosion of iron leads first to the formation of ferrous hydroxide (green 2 rust) and can be described by the following reaction: Fe + 2 H O → Fe(OH) + H 2 2 2 In its turn, under anaerobic conditions, the ferrous hydroxide (Fe(OH) ) can be oxidized by the protons of water to 2 form magnetite and molecular hydrogen. This process is described by the Schikorr reaction: 3 Fe(OH) → Fe O + 2 H O + H 2 3 4 2 2 ferrous hydroxide → magnetite + water + hydrogen The well crystallized magnetite (Fe O ) is thermodynamically more stable than the ferrous hydroxide (Fe(OH) ). 3 4 2 This process occurs during the anaerobic corrosion of iron and steel in oxygen-free groundwater and in reducing soils below the water table.

Geological occurrence: the serpentinization reaction In the absence of atmospheric oxygen (O ), in deep geological conditions prevailing far away from Earth 2 atmosphere, hydrogen (H ) is produced during the process of serpentinization by the anaerobic oxidation by the 2 water protons (H+) of the ferrous (Fe2+) silicate present in the crystal lattice of the fayalite (Fe SiO , the olivine 2 4 iron-endmember). The corresponding reaction leading to the formation of magnetite (Fe O ), quartz (SiO ) and 3 4 2 hydrogen (H ) is the following: 2 3 Fe SiO + 2 H O → 2 Fe O + 3 SiO + 3 H 2 4 2 3 4 2 2 fayalite + water → magnetite + quartz + hydrogen This reaction closely resembles the Schikorr reaction observed in the anaerobic oxidation of the ferrous hydroxide in contact with water.

Applications Large quantities of H are needed in the petroleum and chemical industries. The largest application of H is for the 2 2 processing ("upgrading") of fossil fuels, and in the production of ammonia. The key consumers of H in the 2 petrochemical plant include hydrodealkylation, hydrodesulfurization, and hydrocracking. H has several other 2 important uses. H is used as a hydrogenating agent, particularly in increasing the level of saturation of unsaturated 2 fats and oils (found in items such as margarine), and in the production of methanol. It is similarly the source of hydrogen in the manufacture of hydrochloric acid. H is also used as a reducing agent of metallic ores.[82] 2 Hydrogen is highly soluble in many rare earth and transition metals[83] and is soluble in both nanocrystalline and amorphous metals.[84] Hydrogen solubility in metals is influenced by local distortions or impurities in the crystal lattice.[85] These properties may be useful when hydrogen is purified by passage through hot palladium disks, but the gas serves as a metallurgical problem as hydrogen solubility contributes in an unwanted way to embrittle many metals,[8] complicating the design of pipelines and storage tanks.[9] Apart from its use as a reactant, H has wide applications in physics and engineering. It is used as a shielding gas in 2 welding methods such as atomic hydrogen welding.[86] [87] H is used as the rotor coolant in electrical generators at 2 power stations, because it has the highest thermal conductivity of any gas. Liquid H is used in cryogenic research, 2 including superconductivity studies.[88] Because H is lighter than air, having a little more than 1⁄ of the density of 2 15 air, it was once widely used as a lifting gas in balloons and airships.[89] In more recent applications, hydrogen is used pure or mixed with nitrogen (sometimes called forming gas) as a tracer gas for minute leak detection. Applications can be found in the automotive, chemical, power generation, aerospace, and telecommunications industries.[90] Hydrogen is an authorized food additive (E 949) that allows food package Hydrogen 12

leak testing among other anti-oxidizing properties.[91] Hydrogen's rarer isotopes also each have specific applications. Deuterium (hydrogen-2) is used in nuclear fission applications as a moderator to slow neutrons, and in nuclear fusion reactions.[60] Deuterium compounds have applications in chemistry and biology in studies of reaction isotope effects.[92] Tritium (hydrogen-3), produced in nuclear reactors, is used in the production of hydrogen bombs,[93] as an isotopic label in the biosciences,[53] and as a radiation source in luminous paints.[94] The triple point temperature of equilibrium hydrogen is a defining fixed point on the ITS-90 temperature scale at 13.8033 kelvins.[95]

Energy carrier Hydrogen is not an energy resource,[96] except in the hypothetical context of commercial nuclear fusion power plants using deuterium or tritium, a technology presently far from development.[97] The Sun's energy comes from nuclear fusion of hydrogen, but this process is difficult to achieve controllably on Earth.[98] Elemental hydrogen from solar, biological, or electrical sources require more energy to make it than is obtained by burning it, so in these cases hydrogen functions as an energy carrier, like a battery. Hydrogen may be obtained from fossil sources (such as methane), but these sources are unsustainable.[96] The energy density per unit volume of both liquid hydrogen and compressed hydrogen gas at any practicable pressure is significantly less than that of traditional fuel sources, although the energy density per unit fuel mass is higher.[96] Nevertheless, elemental hydrogen has been widely discussed in the context of energy, as a possible future carrier of energy on an economy-wide scale.[99] For example, CO sequestration followed by carbon capture and 2 storage could be conducted at the point of H production from fossil fuels.[100] Hydrogen used in transportation 2 would burn relatively cleanly, with some NO emissions,[101] but without carbon emissions.[100] However, the x infrastructure costs associated with full conversion to a hydrogen economy would be substantial.[102]

Semiconductor industry Hydrogen is employed to saturate broken ("dangling") bonds of amorphous silicon and amorphous carbon that helps stabilizing material properties.[103] It is also a potential electron donor in various oxide materials, including ZnO,[104] [105] SnO , CdO, MgO,[106] ZrO , HfO , La O , Y O , TiO , SrTiO , LaAlO , SiO , Al O , ZrSiO , HfSiO , and 2 2 2 2 3 2 3 2 3 3 2 2 3 4 4 SrZrO .[107] 3

Biological reactions H is a product of some types of anaerobic metabolism and is produced by several microorganisms, usually via 2 reactions catalyzed by iron- or nickel-containing enzymes called hydrogenases. These enzymes catalyze the reversible redox reaction between H and its component two protons and two electrons. Creation of hydrogen gas 2 occurs in the transfer of reducing equivalents produced during pyruvate fermentation to water.[108] Water splitting, in which water is decomposed into its component protons, electrons, and oxygen, occurs in the light reactions in all photosynthetic organisms. Some such organisms, including the alga Chlamydomonas reinhardtii and cyanobacteria, have evolved a second step in the dark reactions in which protons and electrons are reduced to form H gas by specialized hydrogenases in the chloroplast.[109] Efforts have been undertaken to genetically modify 2 cyanobacterial hydrogenases to efficiently synthesize H gas even in the presence of oxygen.[110] Efforts have also 2 been undertaken with genetically modified alga in a bioreactor.[111] Hydrogen 13

Safety and precautions Hydrogen poses a number of hazards to human safety, from potential detonations and fires when mixed with air to being an asphyxant in its pure, oxygen-free form.[112] In addition, liquid hydrogen is a cryogen and presents dangers (such as frostbite) associated with very cold liquids.[113] Hydrogen dissolves in many metals, and, in addition to leaking out, may have adverse effects on them, such as hydrogen embrittlement,[114] leading to cracks and explosions.[115] Hydrogen gas leaking into external air may spontaneously ignite. Moreover, hydrogen fire, while being extremely hot, is almost invisible, and thus can lead to accidental burns.[116] Even interpreting the hydrogen data (including safety data) is confounded by a number of phenomena. Many physical and chemical properties of hydrogen depend on the parahydrogen/orthohydrogen ratio (it often takes days or weeks at a given temperature to reach the equilibrium ratio, for which the data is usually given). Hydrogen detonation parameters, such as critical detonation pressure and temperature, strongly depend on the container geometry.[112]

See also • Hydrogen atom • Hydrogen bond • Hydrogen ion • Hydrogen production • Isotopes of hydrogen • Liquid hydrogen • Metallic hydrogen • Solid hydrogen • Fuel cell

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[114] "'Bugs' and hydrogen embrittlement" (http:/ / jstor. org/ stable/ 3970088). Science News (Washington D.C.) 128 (3): 41. 1985-07-20. doi:10.2307/3970088. .

[115] Hayes, B.. "Union Oil Amine Absorber Tower" (http:/ / www. twi. co. uk/ content/ oilgas_casedown29. html) (in en). TWI. . Retrieved 29 January 2010.

[116] "Hydrogen Safety" (http:/ / www. schatzlab. org/ education/ h2safety. html). Humboldt State University. . Retrieved 2010-04-14.

References

See also • Hydrogen piping

References [1] W. H. Johnson, Proc. Royal Soc. (London), 23 (1875), 168 [2] J. O’M. Bockris, Int. J. Hydrogen Energy, 6 (1981), 223 [3] T. K. G. Namboodhiri, Trans. Indian Inst. Metals, 37(1984), 764 [4] B. A. Kolachev, Hydrogen embrittlement of non-ferrous metals, Translated from Russian, Israel Program for scientific translations, (1968) [5] W. J. Pardee and N. E. Paton, Metall. Trans. 11A (1980), 1391 [6] G. A. Nelson, in Hydrogen Damage, C. D. Beachem (Ed.), American Society for Metals, Metals Park, Ohio, (1977), p. 377

[7] The Australian Institute for Non Destructive Testing (AINDT), Detection and Quantification of Hydrogen Damage (http:/ / www. ndt. net/

apcndt2001/ papers/ 1154/ 1154. htm)

[8] SGS Industrial Services, NDT-Hot Hydrogen Attack (http:/ / www. sgs. com/ ndt-hot-hydrogen-attack?serviceId=10149586& lobId=5550) Hydrogen damage 96

External links • A 39-page paper on hydrogen damage of metals by M.R. Louthan, "Hydrogen Embrittlement of Metals: A Primer

for the Failure Analyst", 2008, from U.S. DOE OSTI, 3.4MB available here (http:/ / sti. srs. gov/ fulltext/

WSRC-STI-2008-00062. pdf).

Hydrogen embrittlement

Hydrogen embrittlement is the process by which various metals, most importantly high-strength steel, become brittle and fracture following exposure to hydrogen. Hydrogen embrittlement is often the result of unintentional introduction of hydrogen into susceptible metals during forming or finishing operations. Hydrogen embrittlement is also used to describe the formation of zircaloy hydride. Use of the term in this context is common in the nuclear industry.

Process The mechanism starts with lone hydrogen atoms diffusing through the metal. At high temperatures, the elevated solubility of hydrogen allows hydrogen to diffuse into the metal (or the hydrogen can diffuse in at a low temperature, assisted by a concentration gradient). When these hydrogen atoms re-combine in minuscule voids of the metal matrix to form hydrogen molecules, they create pressure from inside the cavity they are in. This pressure can increase to levels where the metal has reduced ductility and tensile strength up to the point where it cracks open (hydrogen induced cracking, or HIC). High-strength and low-alloy steels, nickel and titanium alloys are most susceptible. Austempered iron is also susceptible. Steel with an ultimate tensile strength of less than 1000 MPa or hardness of less than 30 HRC are not generally considered susceptible to hydrogen embrittlement. Jewett et al.[1] reports the results of tensile tests carried out on several structural metals under high-pressure molecular hydrogen environment. These tests have shown that austenitic stainless steels, aluminum (including alloys), copper (including alloys, e.g. beryllium copper) are not susceptible to hydrogen embrittlement along with few other metals[2] . For example of a severe embrittlement measured by Jewett, the elongation at failure of 17-4PH precipitation hardened stainless steel was measured to drop from 17% to only 1.7% when smooth specimens were exposed to high-pressure hydrogen. Hydrogen embrittlement can occur during various manufacturing operations or operational use - anywhere that the metal comes into contact with atomic or molecular hydrogen. Processes that can lead to this include cathodic protection, phosphating, pickling, and electroplating. A special case is arc welding, in which the hydrogen is released from moisture (for example in the coating of the welding electrodes; to minimize this, special low-hydrogen electrodes are used for welding high-strength steels). Other mechanisms of introduction of hydrogen into metal are galvanic corrosion, chemical reactions of metal with acids, or with other chemicals (notably hydrogen sulfide in sulfide stress cracking, or SSC, a process of importance for the oil and gas industries).

Counteractions If the metal has not yet started to crack, the condition can be reversed by removing the hydrogen source and causing the hydrogen within the metal to diffuse out, possibly at elevated temperatures. Susceptible alloys, after chemical or electrochemical treatments where hydrogen is produced, are often subjected to heat treatment to remove absorbed hydrogen. There is a 4-hour time limit for baking out entrapped hydrogen after acid treating the parts. This is the time between the end of acid exposure and the beginning of the heating cycle in the baking furnace. This per SAE AMS 2759/9 Section 3.3.3.1 which calls out the correct procedure for eliminating entrapped hydrogen. In the case of welding, often pre- and post-heating the metal is applied to allow the hydrogen to diffuse out before it can cause any damage. This is specifically done with high-strength steels and low alloy steel such as the Hydrogen embrittlement 97

chrome/molybdenum/vanadium alloys. Due to the time needed to re-combine hydrogen atoms into the harmful hydrogen molecules, hydrogen cracking due to welding can occur over 24 hours after the welding operation is completed. Products such as ferrosilicates can be used to treat surfaces normally subject to hydrogen embrittlement in order to prevent it from taking place.

Related phenomena If steel is exposed to hydrogen at high temperatures, hydrogen will diffuse into the alloy and combine with carbon to form tiny pockets of methane at internal surfaces like grain boundaries and voids. This methane does not diffuse out of the metal, and collects in the voids at high pressure and initiates cracks in the steel. This selective leaching process is known as hydrogen attack, or high temperature hydrogen attack and leads to decarburization of the steel and loss of strength and ductility. Copper alloys which contain oxygen can be embrittled if exposed to hot hydrogen. The hydrogen diffuses through the copper and reacts with inclusions of Cu O, forming H O (water), which then forms pressurized bubbles at the 2 2 grain boundaries. This process can cause the grains to literally be forced away from each other, and is known as steam embrittlement (because steam is produced, not because exposure to steam causes the problem).

Testing There are two ASTM standards for testing embrittlement due to hydrogen gas. The standard ASTM F1459-06 Standard Test Method for Determination of the Susceptibility of Metallic Materials to Hydrogen Gas Embrittlement (HGE) Test [3] uses a diaphragm loaded with a differential pressure. The test ASTM G142-98(2004) Standard Test Method for Determination of Susceptibility of Metals to Embrittlement in Hydrogen Containing Environments at High Pressure, High Temperature, or Both [4] uses a cylindrical tensile specimen tested into an enclosure pressurized with hydrogen or helium. Another ASTM standard exists for quantitatively testing for the Hydrogen Embrittlement threshold stress for the onset of Hydrogen-Induced Cracking due to platings and coatings from Internal Hydrogen Embrittlement (IHE) and Environmental Hydrogen Embrittlement (EHE) [5] - F1624-06 Standard Test Method for Measurement of Hydrogen Embrittlement Threshold in Steel by the Incremental Step Loading Technique. References: ASTM STP 543,"Hydrogen Embrittlement Testing" [6] and ASTM STP 962,"Hydrogen Embrittlement: Prevention and Control." [7] • NACE TM0284-2003 (NACE International) Resistance to Hydrogen-Induced Cracking • ISO 11114-4:2005 (ISO)Test methods for selecting metallic materials resistant to hydrogen embrittlement [8]. • ASTM F1940-07a [9]- Standard Test Method for Process Control Verification to Prevent Hydrogen Embrittlement in Plated or Coated Fasteners • ASTM F519-06e2 [10]-Standard Test Method for Mechanical Hydrogen Embrittlement Evaluation of Plating/Coating Processes and Service Environments Hydrogen embrittlement 98

See also • Hydrogen analyzer • Hydrogen damage • Hydrogen piping • Hydrogen safety • Low hydrogen annealing • Nascent hydrogen

References [1] Jewett, R.P. (1973). Hydrogen Environment Embrittlement of Metals. NASA CR-2163.

[2] Overview of interstate hydrogen pipeline systems-Pag.13 (http:/ / corridoreis. anl. gov/ documents/ docs/ technical/

APT_61012_EVS_TM_08_2. pdf)

[3] http:/ / www. astm. org/ Standards/ F1459. htm

[4] http:/ / www. astm. org/ Standards/ G142. htm

[5] http:/ / www. astm. org/ cgi-bin/ SoftCart. exe/ STORE/ filtrexx40. cgi?U+ mystore+ yvst4574+ -L+ ASTMF1624:06+ / usr6/ htdocs/ astm.

org/ DATABASE. CART/ REDLINE_PAGES/ F1624. htm

[6] http:/ / www. astm. org/ cgi-bin/ SoftCart. exe/ DIGITAL_LIBRARY/ STP/ SOURCE_PAGES/ STP543. htm?L+ mystore+ hsjb1846+ 1193986997

[7] http:/ / www. astm. org/ cgi-bin/ SoftCart. exe/ BOOKSTORE/ PUBS/ 652. htm?E+ mystore

[8] http:/ / www. iso. org/ iso/ en/ CatalogueDetailPage. CatalogueDetail?CSNUMBER=41281& ICS1=23& ICS2=20& ICS3=30

[9] http:/ / www. astm. org/ cgi-bin/ SoftCart. exe/ DATABASE. CART/ REDLINE_PAGES/ F1940. htm?L+ mystore+ yvst4574+ 1196145312

[10] http:/ / www. astm. org/ cgi-bin/ SoftCart. exe/ STORE/ filtrexx40. cgi?U+ mystore+ yvst4574+ -L+ F519+ / usr6/ htdocs/ astm. org/

DATABASE. CART/ REDLINE_PAGES/ F519. htm

Further reading • ASM international, ASM Handbook #13: Corrosion, ASM International, 1998

External links

• Hydrogen embrittlement, revisited by in situ electrochemical nanoindentation (http:/ / www. shaker. de/

online-Gesamtkatalog/ details. asp?ID=8533580& CC=50968& ISBN=3-8322-7834-6)

• Hydrogen embrittlement (http:/ / www. uni-saarland. de/ fak8/ wwm/ research/ phd_barnoush/ hydrogen. pdf)

• Corrosion-Doctors.org Hydrogen embrittlement (http:/ / www. corrosion-doctors. org/ Forms-HIC/ embrittlement. htm)

• Hydrogen purity plays a critical role (http:/ / www. hydrogen. energy. gov/ pdfs/ progress05/ v_a_4_adams. pdf)

• A Sandia National Lab technical reference manual. (http:/ / www. sandia. gov/ matlsTechRef/ ) Hydrogen leak testing 99 Hydrogen leak testing

Hydrogen leak testing is the normal way in which a hydrogen pressure vessel or installation is checked for leaks or flaws. There are various tests. • The Hydrostatic test, The vessel is filled with a nearly incompressible liquid - usually water or oil - and examined for leaks or permanent changes in shape. The test pressure is always considerably more than the operating pressure to give a margin for safety, typically 150% of the operating pressure. • The Burst test, The vessel is filled with a gas and tested for leaks. The test pressure is always considerably more than the operating pressure to give a margin for safety, typically 200% or more of the operating pressure. • The Helium leak test, The leak detection method uses helium (the lightest inert gas) as a tracer gas and detects it in concentrations as small as one part in 10 million. The helium is selected primarily because it penetrates small leaks readily. • Usually a vacuum inside the object is created with an external pump connected to the instrument. • Alternatively helium can be injected inside the product while the product itself is enclosed in a vacuum chamber connected to the instrument. In this case Burst and leakage tests can be combined in one operation. • The Hydrogen sensor, The object is filled with a mixture of 5% hydrogen/ 95% nitrogen, (below 5.7% hydrogen is non-flammable (ISO-10156). This is called typically a sniffing test. The handprobe connected to the microelectronic hydrogen sensors is used to check the object. An audiosignal increases in proximity of a leak. Detection of leaks go down to 5x10-7 cubic centimeters per second [1]. Compared to the helium test: hydrogen is cheaper than helium, no need for a vacuum, the instrument could be cheaper.

See also • Hydrogen analyzer • Hydrogen piping • Hydrogen safety • Tubing (material) • Hydrogen station • Tracer-gas leak testing method

External links • Fibre gratings for hydrogen sensing [2] • Wide-Range Hydrogen Sensor [3] • Wireless sensor [4] • / Hydrogen leak tester [5]

References

[1] http:/ / www. reedlink. com/ SingleArticle~ContentId~11957~pub~IA. html

[2] http:/ / ej. iop. org/ links/ q63/ ,,,vhEqvhL1tjxru6ReiaQ/ mst6_5_s31. pdf

[3] http:/ / www. sandia. gov/ mstc/ technologies/ microsensors/ hydrogensensor. html

[4] http:/ / news. ufl. edu/ 2006/ 05/ 24/ hydrogen-sensor/

[5] http:/ / www. directindustry. com/ prod/ ateq/ hydrogen-leak-detector-7689-258533. html Hydrogen safety 100 Hydrogen safety

Hydrogen safety covers the safe use and handling of hydrogen. Hydrogen poses unique challenges due to its ease of leaking, low-energy ignition, wide range of combustible fuel-air mixtures, buoyancy, and its ability to embrittle metals that must be accounted for to ensure safe operation. Liquid hydrogen poses additional challenges due to its increased density and extremely low temperatures.

Hydrogen codes and standards Hydrogen codes and standards are codes and standards (RCS) for hydrogen fuel cell vehicles, stationary fuel cell applications and portable fuel cell applications. Additional to the codes and standards for hydrogen technology products, there are codes and standards for hydrogen safety, for the safe handling of hydrogen[1] and the storage of hydrogen. • Standard for the installation of stationary fuel cell power systems (National Fire Protection Association)

Guidelines The current ANSI/AIAA standard for hydrogen safety guidelines is AIAA G-095-2004, Guide to Safety of Hydrogen and Hydrogen Systems[2] . As NASA has been one of the world's largest users of hydrogen, this evolved from NASA's earlier guidelines, NSS 1740.16 (8719.16).[3] These documents cover both the risks posed by hydrogen in its different forms and how to ameliorate them.

Ignition • "Hydrogen-air mixtures can ignite with very low energy input, 1/10th that required igniting a gasoline-air mixture. For reference, an invisible spark or a static spark from a person can cause ignition." • "Although the autoignition temperature of hydrogen is higher than those for most hydrocarbons, hydrogen's lower ignition energy makes the ignition of hydrogen–air mixtures more likely. The minimum energy for spark ignition at atmospheric pressure is about 0.02 millijoules."

Mixtures • "The flammability limits based on the volume percent of hydrogen in air at 14.7 psia (1 atm, 101 kPa) are 4.0 and 75.0. The flammability limits based on the volume percent of hydrogen in oxygen at 14.7 psia (1 atm, 101 kPa) are 4.0 and 94.0." • "Explosive limits of hydrogen in air are 18.3 to 59 percent by volume" • "Flames in and around a collection of pipes or structures can create turbulence that causes a deflagration to evolve into a detonation, even in the absence of gross confinement." (For comparison: Deflagration limit of gasoline in air: 1.4–7.6%; of acetylene in air[4] , 2.5% to 82%) Hydrogen safety 101

Leaks • Leakage, diffusion, and buoyancy: These hazards result from the difficulty in containing hydrogen. Hydrogen diffuses extensively, and when a liquid spill or large gas release occurs, a combustible mixture can form over a considerable distance from the spill location. • Hydrogen, in both the liquid and gaseous states, is particularly subject to leakage because of its low viscosity and low molecular weight (leakage is inversely proportional to viscosity). Because of its low viscosity alone, the leakage rate of liquid hydrogen is roughly 100 times that of JP-4 fuel, 50 times that of water, and 10 times that of liquid nitrogen. • Hydrogen leaks can support combustion at very low flow rates, as low as 4 micrograms/s.[5]

Liquid hydrogen • "Condensed and solidified atmospheric air, or trace air accumulated in manufacturing, contaminates liquid hydrogen, thereby forming an unstable mixture. This mixture may detonate with effects similar to those produced by trinitrotoluene (TNT) and other highly explosive materials" Liquid Hydrogen requires complex storage technology such as the special thermally insulated containers and requires special handling common to all cryogenic substances. This is similar to, but more severe than liquid oxygen. Even with thermally insulated containers it is difficult to keep such a low temperature, and the hydrogen will gradually leak away. (Typically it will evaporate at a rate of 1% per day.[6])

Prevention Hydrogen collects under roofs and overhangs, where it forms an explosion hazard; any building that contains a potential source of hydrogen should have good ventillation, strong ignition suppression systems for all electric devices, and preferably be designed to have a roof that can be safely blown away from the rest of the structure in an explosion. It also enters pipes and can follow them to their destinations. Hydrogen pipes should be located above other pipes to prevent this occurrence. Hydrogen sensors allow for rapid detection of hydrogen leaks to ensure that the hydrogen can be vented and the source of the leak tracked down. As in natural gas, an odorant can be added to hydrogen sources to enable leaks to be detected by smell. While hydrogen flames can be hard to see with the naked eye, they show up readily on UV/IR flame detectors.

Accidents Hydrogen has been feared in the popular press as a relatively more dangerous fuel, and hydrogen in fact has the widest explosive/ignition mix range with air of all the gases except acetylene. However this can be mitigated by the fact that hydrogen rapidly rises and disperses before ignition. Unless the escape is in an enclosed, unventilated area, it is unlikely to be serious. Hydrogen also usually rapidly escapes after containment breach. Additionally, hydrogen flames are difficult to see, so may be difficult to fight. An experiment performed at the University of Miami attempted to counter this by showing that hydrogen escapes while gasoline remains by setting alight hydrogen- and petrol-fuelled vehicles.[7] In a more recent event, an explosion of compressed hydrogen during delivery at the Muskingum River Coal Plant (owned and operated by AEP) caused significant damage and killed one person.[8] [9] For more information on incidents involving hydrogen, visit the US DOE's Hydrogen Incident Reporting and Lessons Learned page. [10] Hydrogen safety 102

See also • Hydrogen embrittlement • Hydrogen economy • Compressed hydrogen • Liquid hydrogen • Slush hydrogen • Metallic hydrogen

References

[1] HySafe Initial Guidance for Using Hydrogen in Confined Spaces (http:/ / www. hysafe. org/ download/ 1710/ HYSAFE_D113_version_1. 1. pdf)

[2] "AIAA G-095-2004, Guide to Safety of Hydrogen and Hydrogen Systems" (http:/ / aero-defense. ihs. com/ document/ abstract/ GFEIHBAAAAAAAAAA) (PDF). AIAA. . Retrieved 2008-07-28.

[3] Gregory, Frederick D. (Feb. 12, 1997). "Safety Standard for Hydrogen and Hydrogen Systems" (http:/ / www. hq. nasa. gov/ office/ codeq/

doctree/ canceled/ 871916. pdf) (PDF). NASA. . Retrieved 2008-05-09.

[4] http:/ / www. msha. gov/ alerts/ hazardsofacetylene. htm [5] M.S. Butler, C.W. Moran, Peter B. Sunderland, R.L. Axelbaum, Limits for Hydrogen Leaks that Can Support Stable Flames, International Journal of Hydrogen Energy 34 (2009) 5174-5182.

[6] http:/ / www. almc. army. mil/ alog/ issues/ MayJun00/ MS492. htm

[7] "Hydrogen Car Fire Surprise" (http:/ / www. evworld. com/ article. cfm?storyid=482). January 18, 2003. . Retrieved 2008-05-09.

[8] Williams, Mark (January 8, 2007). ""Ohio Power Plant Blast Kills 1, Hurts 9"" (http:/ / www. washingtonpost. com/ wp-dyn/ content/ article/

2007/ 01/ 08/ AR2007010800350. html). Associated Press. . Retrieved 2008-05-09.

[9] "Muskingum River Plant Hydrogen Explosion January 8, 2007" (http:/ / web. archive. org/ web/ 20080409155509/ http:/ / www. eei. org/

meetings/ nonav_2007-04-29-cs/ Citations_Accident_Review. pdf) (PDF). American Electric Power. November 11, 2006. Archived from the

original (http:/ / www. eei. org/ meetings/ nonav_2007-04-29-cs/ Citations_Accident_Review. pdf) on 2008-04-09. . Retrieved 2008-05-09.

[10] ""Hydrogen Incident Reporting and Lessons Learned"" (http:/ / www. h2incidents. org/ ). .

External links

• Hysafe (http:/ / www. hysafe. org/ )

• Hydrogen and fuelcell safety (http:/ / www. hydrogenandfuelcellsafety. info)

• DOE-Hydrogen safety for First Responders (http:/ / www. ehammertraining. us/ energy/ h2_login/ login. cfm)

• First Responders - Emergency Response Guidebook - Guide 115 (http:/ / hazmat. dot. gov/ pubs/ erg/

erg2008_eng. pdf)

• World's First Higher Educational Programme in Hydrogen Safety Engineering (http:/ / www. hysafe. org/ MScHSE) 103

Fuel

Timeline of hydrogen technologies

Timeline of hydrogen technologies A timeline of the history of hydrogen technology.

Timeline

1600s • 1625 - First description of hydrogen by Johann Baptista van Helmont. First to use the word "gas". • 1650 - Turquet de Mayerne obtained by the action of dilute sulphuric acid on iron a gas or "inflammable air". • 1662 - Boyle's law (gas law relating pressure and volume) • 1670 - Robert Boyle produced hydrogen by reacting metals with acid. • 1672 - "New Experiments touching the Relation between Flame and Air" by Robert Boyle. • 1679 - Denis Papin - safety valve

1700s • 1700 - Nicolas Lemery showed that the gas produced in the sulfuric acid/iron reaction was explosive in air • 1755 - Joseph Black confirmed that different gases exist. / Latent heat • 1766 - Henry Cavendish published in "On Factitious Airs" a description of "dephlogisticated air" by reacting zinc metal with hydrochloric acid and isolated a gas 7 to 11 times lighter than air. • 1774 - Joseph Priestley isolated and categorized oxygen. • 1780 - Felice Fontana discovers the water gas shift reaction • 1783 - Antoine Lavoisier gave hydrogen its name (Gk: hydro = water, genes = born of) • 1783 - Jacques Charles made the first flight with his hydrogen balloon "La Charlière". • 1783 - Antoine Lavoisier and Pierre Laplace measured the heat of combustion of hydrogen using an ice calorimeter. • 1784 - Jean-Pierre Blanchard, attempted a dirigible hydrogen balloon, but it would not steer. • 1784 - The invention of the Lavoisier Meusnier iron-steam process[1] , generating hydrogen by passing water vapor over a bed of red-hot iron at 600 °Cdoi:10.1080/00033798300200381. • 1785 - Jean-François Pilâtre de Rozier built the hybrid Rozière balloon. • 1787 - Charles's law (Gas law, relating volume and temperature) • 1789 - Jan Rudolph Deiman and Adriaan Paets van Troostwijk using a electrostatic machine and a Leyden jar for the first electrolysis of water. Timeline of hydrogen technologies 104

1800s • 1800 - William Nicholson and Anthony Carlisle decomposed water into hydrogen and oxygen by electrolysis with a voltaic pile. • 1800 - Johann Wilhelm Ritter duplicated the experiment with a rearranged set of electrodes to collect the two gases separately. • 1806 - François Isaac de Rivaz built the first internal combustion engine powered by a mixture of hydrogen and oxygen. • 1809 - Thomas Foster observed with a theodolite the drift of small free pilot balloons filled with "inflammable gas"[2] [3] • 1809 - Gay-Lussac's law (Gas law, relating temperature and pressure) • 1811 - Amedeo Avogadro - Avogadro's law a gas law • 1819 - Edward Daniel Clarke invented the hydrogen gas blowpipe. • 1820 - W. Cecil wrote a letter "On the application of hydrogen gas to produce a moving power in machinery"[4] [5]

• 1823 - Goldsworthy Gurney demonstrated Limelight. • 1823 - Döbereiner's Lamp a lighter invented by Johann Wolfgang Döbereiner. • 1823 - Goldsworthy Gurney devised an oxy-hydrogen blowpipe. • 1824 - Michael Faraday invented the rubber balloon. • 1826 - Thomas Drummond built the Drummond Light. • 1826 - Samuel Brown tested his internal combustion engine by using it to propel a vehicle up Shooter's Hill • 1834 - Michael Faraday published Faraday's laws of electrolysis. • 1834 - Benoît Paul Émile Clapeyron - Ideal gas law • 1836 - John Frederic Daniell invented a primary cell in which hydrogen was eliminated in the generation of the electricity. • 1839 - Christian Friedrich Schönbein published the principle of the fuel cell in the "Philosophical Magazine". • 1839 - William Robert Grove developed the Grove cell. • 1842 - William Robert Grove developed the first fuel cell (which he called the gas voltaic battery) • 1849 - Eugene Bourdon - Bourdon gauge (manometer) • 1863 - Etienne Lenoir made a test drive from Paris to Joinville-le-Pont with the 1-cylinder, 2-stroke Hippomobile. • 1866 - August Wilhelm von Hofmann invents the Hofmann voltameter for the electrolysis of water. • 1873 - Thaddeus S. C. Lowe - Water gas, the process used the water gas shift reaction. • 1874 - Jules Verne - The Mysterious Island, "water will one day be employed as fuel, that hydrogen and oxygen of which it is constituted will be used"[6] • 1884 - Charles Renard and Arthur Constantin Krebs launch the airship La France. • 1885 - Zygmunt Florenty Wróblewski published hydrogen's critical temperature as 33 K; critical pressure, 13.3 atmospheres; and boiling point, 23 K. • 1889 - Ludwig Mond and Carl Langer coined the name fuel cell and tried to build one running on air and Mond gas. • 1893 - Friedrich Wilhelm Ostwald experimentally determined the interconnected roles of the various components of the fuel cell. • 1895 - Hydrolysis • 1896 - Jackson D.D. and Ellms J.W., hydrogen production by microalgae (Anabaena) • 1896 - Leon Teisserenc de Bort carries out experiments with high flying instrumental weather balloons[7] . • 1897 - Paul Sabatier facilitated the use of hydrogenation with the discovery of the Sabatier reaction. • 1898 - James Dewar liquefied hydrogen by using regenerative cooling and his invention, the vacuum flask at the Royal Institute of London. • 1899 - James Dewar collected solid hydrogen for the first time. Timeline of hydrogen technologies 105

1900s • 1900 - Count Ferdinand von Zeppelin launched the first hydrogen-filled Zeppelin LZ1 airship. • 1901 - Wilhelm Normann introduced the hydrogenation of fats. • 1903 - Konstantin Eduardovich Tsiolkovskii published "The Exploration of Cosmic Space by Means of Reaction Devices"[8] • 1907 - Lane hydrogen producer • 1909 - Count Ferdinand Adolf August von Zeppelin made the first long distance flight with the Zeppelin LZ5. • 1909 - Linde-Frank-Caro process • 1910 - The first Zeppelin passenger flight with the Zeppelin LZ7. • 1910 - Fritz Haber patented the Haber process. • 1912 - The first scheduled international Zeppelin passenger flights with the Zeppelin LZ13. • 1919 - The first Atlantic crossing by airship with the Beardmore HMA R34. • 1920 - Hydrocracking, a plant for the commercial hydrogenation of brown coal is commissioned at Leuna in Germany[9] . • 1923 - Steam reforming, the first synthetic methanol is produced by BASF in Leuna • 1923 - J. B. S. Haldane envisioned in Daedalus; or, Science and the Future "great power stations where during windy weather the surplus power will be used for the electrolytic decomposition of water into oxygen and hydrogen." • 1926 - Partial oxidation, Vandeveer and Parr at the University of Illinois used oxygen in the place of air for the production of syngas. • 1926 - Cyril Norman Hinshelwood described the phenomenon of chain reaction. • 1926 - Umberto Nobile made the first flight over the north pole with the hydrogen airship Norge • 1929 - Paul Harteck and Karl Friedrich Bonhoeffer achieve the first synthesis of pure parahydrogen. • 1930 - Rudolf Erren - Erren engine - GB patent GB364180 - Improvements in and relating to internal combustion engines using a mixture of hydrogen and oxygen as fuel[10] • 1935 - Eugene Wigner and H.B. Huntington predicted metallic hydrogen. • 1937 - The Zeppelin LZ 129 Hindenburg was destroyed by fire. • 1937 - The Heinkel HeS 1 experimental gaseous hydrogen fueled centrifugal jet engine is tested at Hirth in March- the first working jet engine • 1937 - The first hydrogen-cooled turbogenerator went into service at Dayton, Ohio. • 1938 - The first 240 km hydrogen pipeline Rhine-Ruhr [11] . • 1938 - Igor Sikorsky from Sikorsky Aircraft proposed liquid hydrogen as a fuel. • 1939 - Rudolf Erren - Erren engine - US patent 2,183,674 - Internal combustion engine using hydrogen as fuel • 1939 - Hans Gaffron discovered that algae can switch between producing oxygen and hydrogen. • 1943 - Liquid hydrogen is tested as rocket fuel at Ohio State University. • 1943 - Arne Zetterström describes hydrox • 1949 - Hydrodesulfurization (Catalytic reforming is commercialized under the name Platforming process) • 1952 - Hydrogen maser • 1952 - Non-Refrigerated transport Dewar • 1955 - W. Thomas Grubb modified the fuel cell design by using a sulphonated polystyrene ion-exchange membrane as the electrolyte. • 1957 - Pratt & Whitney's model 304 jet engine using liquid hydrogen as fuel tested for the first time as part of the Lockheed CL-400 Suntan project.[12] • 1957 - The specifications for the U-2 a double axis liquid hydrogen semi-trailer were issued[13] . • 1958 - Leonard Niedrach devised a way of depositing platinum onto the membrane, this became known as the Grubb-Niedrach fuel cell • 1958 - Allis-Chalmers demonstrated the D 12, the first 15 kW fuel cell tractor[14] . Timeline of hydrogen technologies 106

• 1959 - Francis Thomas Bacon built the Bacon Cell, the first practical 5 kW hydrogen-air fuel cell to power a welding machine. • 1960 - Allis-Chalmers builds the first fuel cell forklift[15] • 1961 - RL-10 liquid hydrogen fuelled rocket engine first flight • 1964 - Allis-Chalmers built a 750-watt fuel cell to power a one-man underwater research vessel[16] . • 1965 - The first commercial use of a fuel cell in Project Gemini. • 1965 - Allis-Chalmers builds the first fuel cell golf carts. • 1966 - Slush hydrogen • 1966 - J-2 (rocket engine) liquid hydrogen rocket engine flies • 1967 - Akira Fujishima discovers the Honda-Fujishima effect which is used for photocatalysis in the photoelectrochemical cell. • 1967 - Hydride compressor • 1970 - Nickel hydrogen battery [17] • 1970 - John Bockris or Lawrence W. Jones coined the term hydrogen economy [18] [19] • 1973 - The 30 km hydrogen pipeline in Isbergues • 1973 - Linear compressor • 1975 - John Bockris - Energy The Solar-Hydrogen Alternative - ISBN 0470084294 • 1979 - HM7B rocket engine • 1981 - Space Shuttle main engine first flight • 1990 - The first solar-powered hydrogen production plant Solar-Wasserstoff-Bayern became operational. • 1996 - Vulcain rocket engine • 1997 - Anastasios Melis discovered that the deprivation of sulfur will cause algae to switch from producing oxygen to producing hydrogen • 1998 - Type 212 submarine • 1999 - Hydrogen pinch

2000s • 2000 - Peter Toennies demonstrates superfluidity of hydrogen at 0.15 K • 2001 - The first type IV hydrogen tanks for compressed hydrogen at 700 Bar (10000 PSI) were demonstrated. • 2002 - Type 214 submarine • 2004 - DeepC • 2005 - Ionic liquid piston compressor

See also • Timeline of low-temperature technology • List of timelines

References

[1] 1784 Experiments (http:/ / moro. imss. fi. it/ lavoisier/ Lavoisier_Experiments2Gb. asp?anno=1784)

[2] 1809 - Fleming, History of Meteorology 25 Pag. 25 (http:/ / www. colby. edu/ sts/ st215/ history_of_meteorology. pdf)

[3] 1809 - Pilot balloon resources (http:/ / www. csulb. edu/ ~mbrenner/ history. htm)

[4] 1820 Cecil engine (http:/ / www. eng. cam. ac. uk/ DesignOffice/ projects/ cecil/ engine. html)

[5] 1820 Cecil the letter (http:/ / www. eng. cam. ac. uk/ DesignOffice/ projects/ cecil/ cecil. pdf)

[6] 1874 - Jules Verne, The Mysterious Island (http:/ / www. online-literature. com/ verne/ mysteriousisland/ 33/ )

[7] 1896 Weather balloon (http:/ / www. metoffice. gov. uk/ corporate/ pressoffice/ anniversary/ balloon. html) [8] Tsiolkovsky's Исследование мировых пространств реактивными приборами - The Exploration of Cosmic Space by Means of Reaction

Devices (Russian paper) (http:/ / epizodsspace. testpilot. ru/ bibl/ dorev-knigi/ ciolkovskiy/ issl-03st. html)

[9] 1920 - Hydrocracking (http:/ / www. cheresources. com/ refining5. shtml) Timeline of hydrogen technologies 107

[10] Improvements in and relating to internal combustion engines using a mixture of hydrogen and oxygen as fuel (http:/ / www. wikipatents.

com/ gb/ 0364180. html)

[11] The Technological Steps of Hydrogen Introduction - pag 24 (http:/ / www. storhy. net/ train-in/ PDF-TI/

03_StorHy-Train-IN-Session-1_3_JToepler. pdf)

[12] Sloop, John L. (1978). Liquid hydrogen as a propulsion fuel, 1945-1959.(The NASA history series) (NASA SP-4404) (http:/ / www. hq. nasa.

gov/ office/ pao/ History/ SP-4404/ ch8-9. htm). National Aeronautics and Space Administration. pp. 154–157. .

[13] NASA-LIQUID HYDROGEN AS A PROPULSION FUEL,1945-1959 (http:/ / history. nasa. gov/ SP-4404/ ch8-11. htm)

[14] 1958 D 12 - Pag. 7 (http:/ / www. fuelcelltoday. com/ media/ pdf/ archive/ Article_1152_Fuel Cell History part 2 with illustrations. pdf)

[15] 1960 -Fleet module Pag.3 (http:/ / www. hydrogenassociation. org/ general/ fleet_Module7. pdf)

[16] 1964 Allis Chalmers Pag.1 (http:/ / www. aesc-inc. com/ download/ Ishii_Fuel_Cell_Paper. pdf)

[17] Nickel-Hydrogen Battery Technology—Development and Status (http:/ / pdf. aiaa. org/ jaPreview/ JE/ 1982/ PVJAPRE62569. pdf)

[18] History of Hydrogen (http:/ / www. getenergysmart. org/ Files/ Schools/ Hydrogen/ 3HistoryofHydrogen. pdf)

[19] Lawrence W. Jones Toward a liquid hydrogen fuel economy (http:/ / deepblue. lib. umich. edu/ handle/ 2027. 42/ 5800), University of Michigan Engineering Technical Report UMR2320, March 13, 1970

Biohydrogen

Biohydrogen is defined as hydrogen produced biologically, most commonly by bacteria. Biohydrogen is a potential biofuel obtainable from waste organic materials.[1] More generally the term biohydrogen describes the hydrogen produced via a number of biological processes.

Introduction

Currently, there is a huge demand of the chemical hydrogen. There is no log on the production volume and use of hydrogen world-wide. However the estimated consumption of hydrogen is expected to reach 900 billion cubic meters in 2011[2] Refineries are large-volume producers and consumers of hydrogen. Today 96% of all hydrogen is derived from fossil fuels, with 48% from natural gas, 30% from hydrocarbons, 18% from coal and about 4% from electrolysis. Microbial hydrogen production. Oil-sands processing, gas-to-liquids and coal gasification projects that are ongoing, require a huge amount of hydrogen and is expected to boost the requirement significantly within the next few years. Environmental regulations implemented in most countries, increase the hydrogen requirement at refineries for gas-line and diesel desulfurization[2] [3]

A important future application of hydrogen could be as an alternative for fossil fuels, once the oil deposits are depleted.[4] This application is however dependent on the development of storage techniques to enable proper storage, distribution and combustion of hydrogen.[4] If the cost of hydrogen production, distribution, and end-user technologies decreases, hydrogen as a fuel could be entering the market in 2020.[5] Industrial fermentation of hydrogen, or whole-cell catalysis, requires a limited amount of energy, since fission of water is achieved with whole cell catalysis, to lower the activation energy.[6] This allows hydrogen to be produced from any organic material that can be derived through whole cell catalysis since this process does not depend on the energy of substrate. Biohydrogen 108

Process requirements If hydrogen by fermentation is to be introduced as an industry, the fermentation process will dependent on organic acids as substrate for photo-fermentation. The organic acids are necessary for high hydrogen production rates.[6] [7] The organic acids can be derived from any organic material source such as sewage waste waters or agricultural wastes.[7] The most important organic acids are acetic acid (HAc), butyric acid (HBc) and propionic acid (HPc). A huge advantage is that production of hydrogen by fermentation does not require glucose as substrate.[7] The fermentation of hydrogen has to be a continuous fermentation process, in order sustain high production rates, since the amount of time for the fermentation to enter high production rates are in days.[6]

Fermentation Several strategies for the production of hydrogen by fermentation in lab-scale has been found in literature. However no strategies for industrial-scale productions has been found. In order to define a industrial-scale production, the information from lab-scale experiments has been scaled to a industrial-size production on a theoretical basis. In general, the method of hydrogen fermentation are referred to in three main categories. The first category is dark-fermentation, which is fermentation, which does not involve light. The second category is photo-fermentation, which is fermentation, which require light as the source of energy. The third is combined-fermentation, which refers to the two fermentations combined.

Dark-fermentation There are several bacteria with a potential for hydrogen production. The Gram-positive bacteria of the Clostridium genus, is promising because it has a natural high hydrogen production rate. In addition, it is fast growing and capable of forming spores, which make the bacteria easy to handle in industrial application.[8] Species of the Clostridium genus allow hydrogen production in mixed cultures, under mesophilic or thermophilic conditions within a pH range of 5.0 to 6.5.[8] Dark-fermentation with mixed cultures seems promising since a mixed bacterial environment within the fermenter, allows cooperation of different species to efficiently degrade and convert organic waste materials into hydrogen, accompanied by the formation of organic acids.[8] For the fermentation to be sustainable in industrial-scale, we need to be able to control the bacterial environment inside the fermenter. If the fermentation process is feed with sugar waste, we have a risk, that the feed will contain micro-organisms, which could change the bacterial environment inside the fermenter.[9] A way to prevent harmful micro-organisms from gaining control of the bacterial environment inside the fermenter could be through addition of probiotics which favors or promotes the intended bacterial environment and prevents harmful micro-organisms from gaining control of the fermenter.[9] The dilution rate has to ensure that the amount of biomass inside the fermenter is stable and that the organic acids are removed properly with the outlet stream. The organic acids are toxic to the bacteria and huge amounts will interrupted the fermentation process.[8] This fermentation of hydrogen is accompanied production of carbon-dioxide which can be separated from hydrogen with a passive separation process.[10] The fermentation will convert some of the sugar waste into biomass instead of hydrogen.[8] The biomass is however a carbohydrate-rich by-product which can be fed back into the fermenter, to ensure that the process is sustainable.[11] Fermentation of hydrogen by dark-fermentation is restricted by incomplete degradation of organic material, into organic acids and this is why we need the photo-fermentation.[8] The separation of organic acids from biomass in the outlet stream can be done with a settler tank in the outlet stream, where the sludge (biomass) is pumped back into the fermenter to increase the rate of hydrogen production.[11] Biohydrogen 109

Photo-fermentation Photo-fermentation refers to the method of fermentation where light is required as the source of energy. This fermentation relies on photosynthesis to maintain the cellular energy levels. Fermentation by photosynthesis compared to other fermentations has the advantage of light as the source of energy instead of sugar. Sugars are usually available in limited quantities. All plants, algae and some bacteria are capable of utilizing light as the source of energy. Cyanobacteria which is an algae, is frequently mentioned capable of hydrogen production by photosynthesis.[12] However the purple non-sulphur (PNS) bacteria genus Rhodobacter, holds significant promise for the production of hydrogen by fermentation.[6] Studies have shown that Rhodobacter sphaeroides is highly capable of hydrogen production while feeding on organic acids, consuming 98% to 99% of the organic acids during hydrogen production.[6] As for the dark-fermentation the separation of biomass can be done with a settler tank in the outlet stream, where the sludge (biomass) is pumped back into the fermenter to increase the rate of hydrogen production .[11] Currently there is limited experience with photo-fermentation at industrial-scale. Photo-fermentation require light in the ultra-violet (UV) range up to 400 nm.[13] The distribution of light within the industrial scale photo-fermenter has to be designed to prevent self-shading inside the fermenter and to ensure sustainable hydrogen production. A method to ensure proper light distribution and limit self-shading within the fermenter, could be to distribute the light with an optic fiber where light is transferred into the fermenter and distributed from within the fermenter.[14] Photo-fermentation with Rhodobacter sphaeroides require mesophilic conditions.[15] The optic fiber will transfer light and thus heat into the fermenter, but the heat transferred is limited.[14] The design with an ultra-violent light-source has a huge advantage to other fermentations since ultra-violent light has the potential to eliminate foreign micro-organisms and to prevent contamination. This will limit the need of cleaning procedures. However the production rates with photo-fermentation is not as high as with dark-fermentation.

Combined fermentation Combining dark- and photo-fermentation has shown to be the most efficient method to produce hydrogen through fermentation.[16] The combined fermentation allows the organic acids produced during dark-fermentation of waste materials, to be used as substrate in the photo-fermentation process.[6] For industrial fermentation of hydrogen to be economical feasible, by-products of the fermentation process has to be minimized. Combined fermentation has the unique advantage of allowing reuse of the otherwise useless chemical, organic acids, through photosynthesis. As the method for hydrogen production, this method currently holds significant promise.[6]

Metabolic processes The metabolic process for hydrogen production are dependent on the reduction of the metabolite ferredoxin.[17]

4H+ + ferredoxin(ox) → ferredoxin(red) + 2 H 2 For this process to run, ferredoxin has to be recycled through oxidation. The recycling process is dependent on the transfer of electrons from nicotinamide adenine dinucleotide (NADH) to ferredoxin.[17]

2 ferredoxin(red) + 2 NADH → 2 ferredoxin(ox) + H 2 The enzymes that catalyse this recycling process are referred to as hydrogen-forming enzymes and have complex metalloclusters in their active site and require several maturation proteins to attain their active form.[17] The hydrogen-forming enzymes are inactivated by molecular oxygen and most be separated from oxygen, to produce hydrogen.[17] Biohydrogen 110

The three main classes of hydrogen-forming enzymes are [FeFe]-hydrogenase, [NiFe]-hydrogenase and nitrogenase.[17] These enzymes behaves differently in dark-fermentation with Clostridium and photo-fermentation with Rhodobacter. The interplay of these enzymes are the key in hydrogen production by fermentation.

Clostridium The interplay of the hydrogen-forming enzymes in Clostridium is very unique with little or no involvement of nitrogenase. The hydrogen production in this bacteria is mostly due to [FeFe]-hydrogenase, which activity is a hundred times higher than [NiFe]-hydrogenase and a thousand times higher than nitrogenase. [FeFe]-hydrogenase has a Fe-Fe catalytic core with a variety of electron donors and acceptors.[6] [17] The enzyme [NiFe]-hydrogenase in Clostridium, catalyse a reversible oxidation of hydrogen. [NiFe]-hydrogenase is responsible for hydrogen uptake, utilizing the electrons from hydrogen for cellular maintenance.[17] In Clostridium, glucose is broken down into pyruvate and nicotinamide adenine dicleotide (NADH). The formed pyruvate is then further converted to acetyl-CoA and hydrogen by pyruvate ferredoxin oxidoreductase with the reduction of ferredoxin.[17] Acetyl-CoA is then converted to acetate, butyrate and propionate.[17] [18] Acetate fermentation processes are well understood and have a maximum yield of 4 mol hydrogen pr. mol glucose.[6] The yield of hydrogen from the conversion of acetyl-CoA to butyrate, has half the yield as the conversion to acetate.[6] [17] In mixed cultures of Clostridium the reaction is a combined production of acetate, butyrate and propionate.[16] The organic acids which are the by-product of fermentation with Clostridium, can be further processed as substrate for hydrogen production with Rhodobacter.

Rhodobacter The purple non-sulphur bacteria Rhodobacter spharoids is able to produce hydrogen from organic acids and ultra-violet light.[17] The photo-system required for hydrogen production in Rhodobacter (PS-I), differ from its oxygenic photosystem (PS-II) due to the requirement of organic acids and the inability to oxidize water.[17] In Rhodobacter, the hydrogen production is due to catalysis by nitrogenase. The production of hydrogen by [FeFe]-hydrogenase is less than 10 times the hydrogen uptake by [NiFe]-hydrogenase.[19] The interplay of hydrogenase and nitrogenase in this bacteria is responsible for the production of hydrogen and require nitrogen-deficient conditions to produce hydrogen.[17] [19] The main photosynthetic membrane complex is PS-I which accounts for most of the light-harvest. The photosynthetic membrane complex PS-II produces oxygen, which inhibit hydrogen production and thus low partial pressures of oxygen most be sustained during fermentation.[17] To attain high production rates of hydrogen, the hydrogen production by nitrogenase has to exceed the hydrogen uptake by hydrogenase.[19] The substrate is oxidized through the tricarboxylic acids circle and the Rhodobacter hydrogen metabolism produced electrons are transferred to the nitrogenase catalysed reduction of protons to hydrogen, through the electron transport chain.[17] [19] Biohydrogen 111

LED-fermenter A cheap way to build a industrial-size photo-fermenter could be to build a fermenter with ultra-violet light emitting diodes (UV-LED) as light source. This design prevents self-shading within the fermenter, require limited energy to maintain photosynthesis and has very low installation costs. This design would also allow cheap models to be built for educational purpose.

Metabolic engineering There is a huge potential for improving hydrogen yield by metabolic engineering. The bacteria Clostridium could be improved for hydrogen production by disabling the uptake hydrogenase, or disabling the oxygen system. This will make the hydrogen production robust and increase the hydrogen yield in the dark-fermentation step. The photo-fermentation step with Rhodobacter, is the step which is likely to gain the most from metabolic engineering. An option could be to disable the uptake-hydrogenase or to disable the photosynthetic membrane system II (PS-II). Another improvement could be to decrease the expression of pigments, which shields of the photo-system.

See also • Hyvolution • Biological hydrogen production (Algae) • Photobiology • Electrohydrogenesis • Microbial fuel cell • Caldicellulosiruptor saccharolyticus

References [1] Demirbas, A. (2009). Biohydrogen: For Future Engine Fuel Demands. Trabzon: Springer. ISBN 1848825102

[2] Stefan Schlag, Bala Suresh, Masahiro Yoneyama (October 2007). "SRI Consulting CEH Report – Hydrogen" (http:/ / www. sriconsulting.

com/ CEH/ Public/ Reports/ 743. 5000/ ). SRI Consulting. . Retrieved 2010-07-01.

[3] "The National Hydrogen Association" (http:/ / www. hydrogenassociation. org/ general/ faqs. asp#howmuchproduced). Hydrogenassociation.org. 2004-08-13. . Retrieved 2010-07-01.

[4] "Transport and the Hydrogen Economy" (http:/ / www. world-nuclear. org/ info/ inf70. html). World-nuclear.org. . Retrieved 2010-07-01. [5] The iea energy technology essentials are regularly-updated briefs that draw together the best-available, consolidated information on energy technologies from the iea network, April 2007. [6] Tao, Yongzhen; Chen, Yang; Wu, Yongqiang; He, Yanling; Zhou, Zhihua (February 2007). "High hydrogen yield from a two-step process of

dark- and photo-fermentation of sucrose" (http:/ / www. sciencedirect. com/ science/ article/ B6V3F-4KGPP8H-1/ 2/ a2e03311e524ba2baeb47e720d9c47e5). International Journal of Hydrogen Energy 32 (2): 200–206. doi:10.1016/j.ijhydene.2006.06.034. ISSN 0360-3199. .

[7] Kapdan, Ilgi Karapınar; Kargı, Fikret (2006). "Biohydrogen production from waste materials" (http:/ / www. ichet. org/ ihec2005/ files/

manuscripts/ Kargi F. -Tr. pdf). Enzyme and Microbial Technology. . [8] Krupp, M.; Widmann, R (May 2009). "Biohydrogen production by dark fermentation: Experiences of continuous operation in large lab scale". International Journal of Hydrogen Energy 34 (10, Sp. Iss.SI): 4509–4516. doi:10.1016/j.ijhydene.2008.10.043. [9] Verschuere, L; Rombaut,, G; Sorgeloos, P; Verstraete, W (December 2000). "Probiotic bacteria as biological control agents in aquaculture". Microbiology and Molecular Biology Reviews 64 (4): 655+. doi:10.1128/MMBR.64.4.655-671.2000. [10] Watanabe, Hisanori; Yoshino, Hidekichi (May 2010). "Biohydrogen using leachate from an industrial waste landfill as inoculum". Renewable Energy 35 (5): 921–924. doi:10.1016/j.renene.2009.10.033.

[11] Villadsen, John; Nielsen, Jens Høiriis; Lidén, Gunnar (2003). Bioreaction Engineering Principles (http:/ / books. google. com/

?id=htUeM34b7KgC& lpg=PP1& dq=Bioreaction Engineering Principles& pg=PP1#v=onepage& q) (2 ed.). Springer. ISBN 9780306473494. . [12] Lee, Jae-Hwa; Lee, Dong-Geun; Park, Jae-Il; Kim, Ji-Youn (JAN 2010). "Biohydrogen production from a marine brown algae and its bacterial diversity". Korean Journal of Chemical Engineering 27 (1): 187–192. doi:10.1007/s11814-009-0300-x. Biohydrogen 112

[13] Kahn, Amanda E.; Durako, Michael J. (October 2009). "Wavelength-specific photo-synthetic responses of Halophila johnsonii from marine-influenced versus river-influenced habitats". Aquatic Botany 91 (3): 245–249. doi:10.1016/j.aquabot.2009.06.004.

[14] THE NORTH STATE, www.thenorthstate.com. "Sunlight Direct" (http:/ / www. sunlight-direct. com). Sunlight Direct. . Retrieved 2010-07-01. [15] Nath, K; Kumar, A; Das, D (September 2005). "Hydrogen production by Rhodobacter sphaeroides strain OU001 using spent media of Enterobacter cloacae strain DM11". Applied Microbiology and Biotechnology 68 (4): 533–541. doi:10.1007/s00253-005-1887-4. PMID 15666144. [16] Yang, Honghui; Guo,, Liejin; Liu, Fei (March 2010). "Enhanced bio-hydrogen production from corncob by a two-step process: Dark- and photo-fermentation". Bioresource Technology 101 (6): 2049–2052. doi:10.1016/j.biortech.2009.10.078. PMID 19963373. [17] Mathews, Juanita; Wang, Guangyi (September 2009). "Metabolic pathway engineering for enhanced biohydrogen production". International Journal of Hydrogen Energy 34 (17, Sp. Iss. SI): 7404–7416. doi:10.1016/j.ijhydene.2009.05.078.

[18] "KEGG PATHWAY: Pyruvate metabolism - Clostridium acetobutylicum" (http:/ / www. genome. jp/ kegg-bin/ show_pathway?cac00620). Genome.jp. . Retrieved 2010-07-01. [19] Koku, H; Eroglu, I; Gunduz, U; Yucel, M; Turker, L (2002). "Aspects of the metabolism of hydrogen production by Rhodobacter sphaeroides". International Journal of Hydrogen Energy 27 (11-12): 1315–1329. doi:10.1016/S0360-3199(02)00127-1.

External links

• Fermentation of hydrogen (http:/ / www. youtube. com/ watch?v=wKfx3-CpqTQ)

• Production of hydrogen with bacteria (http:/ / www. youtube. com/ watch?v=n_h08Vbdjt4)

• 1999 - Biohydrogen RITE Biological Hydrogen Program (http:/ / www. springerlink. com/ content/

p3u912048n600315/ )

• GTL (http:/ / genomicsgtl. energy. gov/ benefits/ biohydrogen. shtml)

• EU & Dutch Biohydrogen research page (http:/ / www. biohydrogen. nl)

• wasteintoenergy.org (http:/ / www. wasteintoenergy. org)

• University of California Davis -New Technology Turns Food Leftovers Into Electricity, Vehicle Fuels (http:/ /

www. news. ucdavis. edu/ search/ news_detail. lasso?id=7915)

• Onsite Power Systems (http:/ / www. onsitepowersystems. com/ )

• "Appendix 2: Biohydrogen" (http:/ / completebiogas. com/ BiogasHandbook_A02_biohydrogen. pdf) from The Complete Biogas Handbook

• BBSRC- Our Science- Bacteria Make Light Work of Hydrogen Production (http:/ / www. bbsrc. ac. uk/ science/

our_science_explained/ 0906_bacteria_make_light_work_of_hydrogen_production. html)

• Biowaste2energy Ltd is applying biohydrogen (http:/ / www. bw2e. com) Hydrogen production 113 Hydrogen production

Hydrogen production is the industrial method for generating hydrogen. Currently the dominant technology for direct production is steam reforming from hydrocarbons. Hydrogen is also produced as a byproduct of other processes and managed with hydrogen pinch[1] . Many other methods are known including electrolysis and thermolysis. The discovery and development of less expensive methods of production of bulk hydrogen is relevant to the establishment of a hydrogen economy.[2]

Hydrogen waste stream Hydrogen is used for the creation of ammonia for fertilizer via the Haber process, converting heavy petroleum sources to lighter fractions via hydrocracking and petroleum fractions (dehydrocyclization and the aromatization process). It was common to vent the surplus of hydrogen, nowadays the plants are balanced with hydrogen pinch which creates the possibility of collecting the hydrogen for further use. Hydrogen is also produced as a by-product of industrial chlorine production by electrolysis. It can be cooled, compressed and purified for use in other processes on site or sold to a customer via pipeline, cylinders or trucks.

From hydrocarbons

Steam reforming Fossil fuel currently is the main source of hydrogen production[3] . Hydrogen can be generated from natural gas with approximately 80% efficiency, or from other hydrocarbons to a varying degree of efficiency. Specifically, bulk hydrogen is usually produced by the steam reforming of methane or natural gas[4] At high temperatures (700–1100 °C), steam (H O) reacts with methane (CH ) to yield syngas. 2 4 CH + H O → CO + 3 H + 191.7 kJ/mol[5] 4 2 2 In a second stage, further hydrogen is generated through the lower-temperature water gas shift reaction, performed at about 130 °C: CO + H O → CO + H - 40.4 kJ/mol 2 2 2 Essentially, the oxygen (O) atom is stripped from the additional water (steam) to oxidize CO to CO . This oxidation also provides energy to 2 maintain the reaction. Additional heat required to drive the process is generally supplied by burning some portion of the methane. Gasification Steam reforming generates carbon dioxide (CO ). Since the production 2 is concentrated in one facility, it is possible to separate the CO and 2 dispose of it properly, for example by injecting it in an oil or gas reservoir (see carbon capture), although this is not currently done in most cases. A carbon dioxide injection project has been started by a Norwegian company StatoilHydro in the North Sea, at the Sleipner field. However, even if the carbon dioxide is not sequestered, overall producing hydrogen from natural gas and using it for a hydrogen vehicle only emits half the carbon dioxide that a gasoline car would. (This is disputed in The Hype about Hydrogen: Fact and Fiction in the Race to Save the Climate, a book by Joseph J. Romm, published in 2004 by Island Press and updated in 2005. Romm says that directly burning fossil fuels generates less CO than hydrogen production.) 2 Integrated steam reforming / co-generation - It is possible to combine steam reforming and co-generation of steam and power into a single plant. This can deliver benefits for an oil refinery because it is more efficient than separate hydrogen, steam and power plants. Air Products recently built an integrated steam reforming / co-generation plant in Port Arthur, Texas.[6] Hydrogen production 114

Partial oxidation The partial oxidation reaction occurs when a substoichiometric fuel-air mixture is partially combusted in a reformer, creating a hydrogen-rich syngas. A distinction is made between thermal partial oxidation (TPOX) and catalytic partial oxidation (CPOX).

• General reaction equation: • Possible reaction equation (heating oil): • Possible reaction equation (coal):

Plasma reforming The Kværner-process or Kvaerner carbon black & hydrogen process (CB&H)[3] is a plasma reforming method, developed in the 1980s by a Norwegian company of the same name, for the production of hydrogen and carbon black from liquid hydrocarbons (C H ). Of the available energy of the feed, approximately 48% is contained in the n m hydrogen, 40% is contained in activated carbon and 10% in superheated steam.[7] CO is not produced in the process. 2 A variation of this process is presented in 2009 using plasma arc waste disposal technology for the creation of hydrogen, heat and carbon from methane and natural gas in a plasma converter[8]

Coal Coal can be converted into syngas and methane, also known as town gas, via coal gasification. Syngas consists of hydrogen and carbon monoxide.[9] . Another method for conversion is low temperature and high temperature coal carbonization[10] .

From water

Electrolysis and thermolysis Hydrogen is produced on an industrial scale by the electrolysis of water. While this can be done with a few volts in a simple apparatus like a Hofmann voltameter,[11] larger scale production usually relies on high-pressure and high-temperature systems to improve the energy efficiency of electrolysis. Experimental processes include electrolysis at very high temperatures (800 C), so that much of the energy required to release hydrogen is supplied as heat instead of electricity. Various catalytic agents are being studied to improve the efficiency of high-temperature electrolysis. Water spontaneously dissociates at around 2500 C, but this thermolysis occurs at temperatures too high for usual process piping and equipment. Catalysts are required to reduce the dissociation temperature.

Sulfur-Iodine Cycle The sulfur-iodine cycle (S-I cycle) is a thermochemical process which generates hydrogen from water, but at a much higher efficiency than water splitting. The sulfur and iodine used in the process are recovered and reused, and not consumed by the process. It is well suited to production of hydrogen by high-temperature nuclear reactors.

From urine Hydrogen can also be made from urine. Using urine, hydrogen production is 332% more energy efficient than using water.[12] [13] The research was conducted by Geraldine Botte from the Ohio University. Recently, Dr. Shanwen Tao of the Heriot-Watt University has invented a Carbamide Power System Fuel Cell that can immediatelly convert urine into electricity.[14] Hydrogen production 115

Biohydrogen routes Biomass and waste streams can be converted into biohydrogen with biomass gasification, steam reforming or biological conversion like biocatalysed electrolysis or fermentative hydrogen production:

Fermentative hydrogen production Fermentative hydrogen production is the fermentative conversion of organic substrate to biohydrogen manifested by a diverse group bacteria using multi enzyme systems involving three steps similar to anaerobic conversion. Dark fermentation reactions do not require light energy, so they are capable of constantly producing hydrogen from organic compounds throughout the day and night. Photofermentation differs from dark fermentation because it only proceeds in the presence of light. For example photo-fermentation with Rhodobacter sphaeroides SH2C can be employed to convert small molecular fatty acids into hydrogen.[15] Biohydrogen can be produced in bioreactors that utilize feedstocks, the most common feedstock being waste streams. The process involves bacteria feeding on hydrocarbons and exhaling hydrogen and CO . The CO can be 2 2 sequestered successfully by several methods, leaving hydrogen gas. A prototype hydrogen bioreactor using waste as a feedstock is in operation at Welch's grape juice factory in North East, Pennsylvania (U.S.).

Enzymatic hydrogen generation Due to the Thauer limit (four H2/glucose) for dark fermentation, the biochemical engineer -- Y-H Percival Zhang, associate professor at Virginia Tech -- designed a non-natural enzymatic pathway that can generate 12 moles of hydrogen per mole of glucose units of polysaccharides and water in 2007[16] . The stoichiometric reaction is C6H10O5+ 7 H2O --> 12 H2 + 6 CO2. The key technology is cell-free synthetic enzymatic pathway biotransformation (SyPaB)[17] [18] . A biochemist can understand it as "glucose oxidation by using water as oxidant". A chemist can describe it as "water splitting by energy in carbohydrate". A thermodynamics scientist can describe it as the first entropy-driving chemical reaction that can produce hydrogen by absorbing waste heat. In 2009, cellulosic materials were first used to generate high-yield hydrogen[19] . Furthermore, Dr. Zhang proposed the use of carbohydrate as a high-density hydrogen carrier so to solve the largest obstacle to the hydrogen economy and propose the concept of sugar fuel cell vehicles[20] .

Biocatalysed electrolysis

Besides dark fermentation, electrohydrogenesis (electrolysis using microbes) is another possibility. Using microbial fuel cells, wastewater or plants can be used to generate power. Biocatalysed electrolysis should not be confused with biological hydrogen production, as the latter only uses algae and with the latter, the algae itself generates the hydrogen instantly, where with A microbial electrolysis cell biocatalysed electrolysis, this happens after running through the microbial fuel cell and a variety of aquatic plants[21] can be used. These include reed sweetgrass, cordgrass, rice, tomatoes, lupines, algae [22] Hydrogen production 116

Other methods • Synthetic biology [23] [24] [25]

Renewable (or "Green") Hydrogen Production Currently there are several practical ways of producing hydrogen in a renewable industrial process. One is to use landfill gas to produce hydrogen in a steam reformer, and the other is to use renewable power to produce hydrogen from electrolysis. Hydrogen fuel, when produced by renewable sources of energy like wind or solar power, is a renewable fuel [26] .

See also • Ammonia production • Biological hydrogen production • Hydrogen • Hydrogen analyzer • Hydrogen compressor • Hydrogen economy • Hydrogen embrittlement • Hydrogen leak testing • Hydrogen pipeline transport • Hydrogen piping • Hydrogen purifier • Hydrogen purity • Hydrogen safety • Hydrogen sensor • Hydrogen storage • Hydrogen station • Hydrogen tank • Hydrogen tanker • Hydrogen technologies • Hydrogen valve • Industrial gas • Liquid Hydrogen • Next Generation Nuclear Plant (partly for hydrogen production) • The Phoenix Project: Shifting from Oil To Hydrogen (book) • Renewable energy • The Hype about Hydrogen • Lane hydrogen producer • Linde-Frank-Caro process • Liquid nitrogen production • Underground hydrogen storage Hydrogen production 117

References

[1] Waste hydrogen purification and supply (http:/ / www. hydrogenhighway. ca/ code/ navigate. asp?doi=224) [2] Peter Häussinger1, Reiner Lohmüller2, Allan M. Watson “Hydrogen” Ullmann's Encyclopedia of Industrial Chemistry, 2002, Wiley-VCH, Weinheim.

[3] Bellona-HydrogenReport (http:/ / www. interstatetraveler. us/ Reference-Bibliography/ Bellona-HydrogenReport. html)

[4] Fossil fuel processor (http:/ / auto. howstuffworks. com/ fuel-processor. htm)

[5] "HFCIT Hydrogen Production: Natural Gas Reforming" (http:/ / www1. eere. energy. gov/ hydrogenandfuelcells/ production/ natural_gas. html). U.S. Department of Energy. 2008-12-15. .

[6] Port Arthur II Integrated Hydrogen/Cogeneration Facility, Port Arthur, Texas (http:/ / www. airproducts. com/ nr/ rdonlyres/

6226ec23-a536-4603-ab37-2b2ff3f9d45b/ 0/ port_arthur_122212258eprint. pdf) Power magazine, September 2007

[7] https:/ / www. hfpeurope. org/ infotools/ energyinfos__e/ hydrogen/ main03. html

[8] Kværner-process with plasma arc waste disposal technology (http:/ / fuelcellsworks. com/ news/ 2009/ 10/ 12/

hydrogen-breakthrough-for-norwegian-company/ )

[9] "HFCIT Hydrogen Production: Coal Gasification" (http:/ / www1. eere. energy. gov/ hydrogenandfuelcells/ production/ coal_gasification. html). U.S. Department of Energy. 2008-12-12. . [10] [pubs.acs.org/cgi-bin/jtext?enfuem/15/i03/abs/ef990178a Internal gas pressure characteristics generated during coal carbonization in a coke oven]

[11] "Electrolysis of water and the concept of charge" (http:/ / www. practicalphysics. org/ go/ Experiment_677. html). .

[12] Hydrogen from urine (http:/ / www. physorg. com/ news165836803. html) [13] 1,23V/0,37V

[14] Carbamide Power System Fuel Cell (http:/ / www. outlookseries. com/ N8/ Science/

3753_Shanwen_Tao_Heriot-Watt_University_Carbamide_Power_System_Fuel_Cell_Turns_Urine_Electricity_Water_Shanwen_Tao. htm)

[15] High hydrogen yield from a two-step process of dark-and photo-fermentation of sucrose (http:/ / cat. inist. fr/ ?aModele=afficheN& cpsidt=18477081)

[16] (http:/ / dx. doi. org/ 10. 1371/ journal. pone. 0000456)

[17] (http:/ / dx. doi. org/ 10. 1002/ bit. 22630)

[18] (http:/ / dx. doi. org/ 10. 1016/ j. copbio. 2010. 05. 005)

[19] (http:/ / dx. doi. org/ 10. 1002/ cssc. 200900017)

[20] (http:/ / dx. doi. org/ 10. 1039/ b818694d)

[21] aquatic plants (http:/ / www. glastuinbouw. wur. nl/ UK/ expertise/ energy/ innovations/ plantenergy/ )

[22] Power from plants using microbial fuel cell (http:/ / translate. google. com/ translate?js=n& prev=_t& hl=nl& ie=UTF-8& u=http:/ / www.

resource-online. nl/ achtergrond. php?id=147& sl=nl& tl=en& history_state0=)

[23] Synthetic biology and hydrogen (http:/ / www. highbeam. com/ doc/ 1G1-163896478. html)

[24] Synthetic biology to make hydrogen (http:/ / www. guardian. co. uk/ science/ 2008/ jun/ 19/ chemistry. agriculture)

[25] Synthetic biology at Berkeley Lab (http:/ / pbd. lbl. gov/ synthbio/ aims. htm)

[26] National Renewable Energy Laboratory 2003 Research Review: "New Horizons for Hydrogen." (http:/ / www. nrel. gov/ research_review/

pdfs/ 2003/ 36178b. pdf)

External links

• U.S. DOE 2008-Technical progress in hydrogen production (http:/ / www. hydrogen. energy. gov/

annual_progress08_production. html)

• U.S. NREL article on hydrogen production (http:/ / www. nrel. gov/ hydrogen/ proj_production_delivery. html)

• Genetically engineered blood protein can be used to produce hydrogen gas from water (http:/ / www3. imperial.

ac. uk/ newsandeventspggrp/ imperialcollege/ newssummary/ news_1-12-2006-11-4-23?newsid=3016) Hydrogen infrastructure 118 Hydrogen infrastructure

A hydrogen infrastructure is the infrastructure of pipes and stations for distribution and sale of hydrogen fuel.

Network

Hydrogen pipeline transport Hydrogen pipeline transport is a transportation of hydrogen through a pipe as part of the hydrogen infrastructure. Hydrogen pipeline transport is used to connect the point of hydrogen production or delivery of hydrogen with the point of demand, pipeline transport costs are similar to CNG[1] , the technology is proven[2] , however most hydrogen is produced on the place of demand with every 50 to 100 miles an industrial production facility.[3] . As of 2004 there are 900 miles (1450 km) of low pressure hydrogen pipelines in the USA and 930 miles in Europe.

Hydrogen highway A hydrogen highway is a chain of hydrogen-equipped filling stations and other infrastructure along a road or highway which allow hydrogen vehicles to travel.

Hydrogen stations Hydrogen stations which are not situated near a hydrogen pipeline get supply via hydrogen tanks, compressed hydrogen tube trailers, liquid hydrogen trailers, liquid hydrogen tank trucks or dedicated onsite production. Some firms as ITM Power are also providing solutions to make your own hydrogen (for use in the car) at home.[4] South Carolina also has a hydrogen freeway in the works. There are currently two hydrogen fueling stations, both in Aiken and Columbia, SC. Additional stations are expected in places around South Carolina such as Charleston, Myrtle Beach, Greenville, and Florence. According to the South Carolina Hydrogen & Fuel Cell Alliance, the Columbia station has a current capacity of 120 kg a day, with future plans to develop on-site hydrogen production from electrolysis and reformation. The Aiken station has a current capacity of 80 kg. There is extensive funding for Hydrogen fuel cell research and infrastructure in South Carolina. The University of South Carolina, a founding member of the South Carolina Hydrogen & Fuel Cell Alliance, received 12.5 million dollars from the Department of Energy for its Future Fuels Program.[5] The California Hydrogen Highway is an initiative by the California Governor to implement a series of hydrogen refueling stations along that state. These stations are used to refuel hydrogen vehicles such as fuel cell vehicles and hydrogen combustion vehicles. As of July 2007 California had 179 fuel cell vehicles and twenty five stations were in operation,[6] and ten more stations have been planned for assembly in California. However, there have already been three hydrogen fueling stations decommissioned.[7] In May 2010, UNIDO has launched, on behalf of the International Centre for Hydrogen Energy Technologies, a call for tender related to the supply and installation by the end of 2011 of a hydrogen production, storage and filling facility on the Golden Horn, in Istanbul. This station will be used for the refueling of a hydrogen fuel cell driven passenger boat as well as for that of a hydrogen internal combustion bus.[8] Hydrogen infrastructure 119

See also • HCNG dispenser • Hydrogen piping • Hydrogen economy • Underground hydrogen storage

References

[1] Compressorless Hydrogen Transmission Pipelines (http:/ / www. leightyfoundation. org/ files/ WHEC16-Lyon/ WHEC16-Ref022. pdf)

[2] DOE Hydrogen Pipeline Working Group Workshop (http:/ / www1. eere. energy. gov/ hydrogenandfuelcells/ pdfs/ hpwgw_airprod_remp. pdf)

[3] Every 50 to 100 miles (http:/ / www. hydrogenforecast. com/ ArticleDetails. php?articleID=250)

[4] Running on home-brewed hydrogen (http:/ / news. bbc. co. uk/ 2/ hi/ technology/ 7496644. stm)

[5] Cluster Successes in South Carolina (http:/ / www. schydrogen. org/ documents/ Reports/ Cluster_Successes. pdf)

[6] "California Fuel Cell Partnership" (http:/ / www. cafcp. org). .

[7] "Hydrogen Fueling Stations" (http:/ / www. cafcp. org/ fuel-vehl_map. html). .

[8] "Golden Horn Refuelling Station" (http:/ / www. unido-ichet. org. org/ index. php?lang=en& Itemid=42& option=com_content&

id=401:golden-horn-refuelling-station& view=article). .

External links

• The Hydrogen Infrastructure Transition (HIT) Model (http:/ / pubs. its. ucdavis. edu/ publication_detail. php?id=140)

• Roads2HyCom Infrastructure (http:/ / www. ika. rwth-aachen. de/ r2h/ index. php/ European_Hydrogen_Infrastructure_and_Production)

Hydrogen line

The hydrogen line, 21 centimeter line or HI line refers to the electromagnetic radiation spectral line that is created by a change in the energy state of neutral hydrogen atoms. This electromagnetic radiation is at the precise frequency of 1420.40575177 MHz, which is equivalent to the vacuum wavelength of 21.10611405413 cm in free space. This wavelength or frequency falls within the microwave radio region of the electromagnetic spectrum, and it is observed frequently in radio astronomy, since those radio waves can penetrate the large clouds of interstellar cosmic dust that are opaque to visible light. Note that the relationship between the frequency and the wavelength is found from the simple equation that says that the wavelength equals c (the speed of light) divided by the frequency measured in hertz. The microwaves of the hydrogen line comes from the atomic transition between the two hyperfine levels of the hydrogen 1s ground state.[1] There is a difference in energy between these two hyperfine levels, and the frequency of the quanta that are emitted is given by Planck's equation. Hydrogen line 120

Cause

Origin of Neutral Hydrogen Emission

An electron orbiting a proton with parallel spins (pictured) has higher Fine and hyperfine structure in energy than if the spins were anti-parallel. hydrogen. The hyperfine splitting of the ground 2S state is the source of the 21 cm hydrogen line.

Electron transitions and their resulting wavelengths for Hydrogen. Energy levels are not to scale.

Neutral hydrogen consists of a single proton orbited by a single electron. As well as their orbital motion, the proton and electron also have spin. Classically, this is analogous to rotational motion (like the Earth rotating on its axis as it orbits the Sun), but as they are quantum particles the concept has a slightly different meaning. The spin of the electron and proton can be in either direction - in the classical analogy they are rotating clockwise or anticlockwise around a given axis. They may have their spin oriented in the same direction or in opposite directions. Because of magnetic interactions between the particles, a hydrogen atom that has the spins of the electron and proton aligned in the same direction (parallel) has slightly more energy than one where the spins of the electron and proton are in opposite directions (anti-parallel). The fact that the lowest-energy configuration arises in the anti-parallel spin configuration is an inherently quantum-mechanical result. A proton and electron with anti-parallel spins have parallel magnetic moments owing to their opposite charge. Classical mechanics would predict that this configuration should have higher energy, but a more detailed quantum mechanical analysis shows that the opposite is true. The lowest orbital energy state of atomic hydrogen has hyperfine splitting arising from the spins of the proton and electron changing from a parallel to antiparallel configuration. This transition is highly forbidden with an extremely small probability of 2.9×10−15 s−1. This means that the time for a single isolated atom of neutral hydrogen to undergo this transition is around 10 million (107) years and so is unlikely to be seen in a laboratory on Earth. However, as the total number of atoms of neutral hydrogen in the interstellar medium is very large, this emission line is easily observed by radio telescopes. Also, the Hydrogen line 121

lifetime can be considerably shortened by collisions with other hydrogen atoms and interaction with the cosmic microwave background. The line has an extremely small natural width because of its long lifetime, so most broadening is due to doppler shifts caused by the motion of the emitting regions relative to the observer.

Discovery During the 1930s, it was noticed that there was a radio 'hiss' that varied on a daily cycle and appeared to be extraterrestrial in origin. After initial suggestions that this was due to the Sun, it was observed that the radio waves seemed to be coming from the centre of the Galaxy. These discoveries were published in 1940 and were seen by Professor J.H. Oort who knew that significant advances could be made in astronomy if there were emission lines in the radio part of the spectrum. He referred this to Dr Hendrik van de Hulst who, in 1944, predicted that neutral hydrogen could produce radiation at a frequency of 1420.4058 MHz due to two closely spaced energy levels in the ground state of the hydrogen atom. The 21 cm line (1420.4 MHz) was first detected in 1951 by Ewen and Purcell at Harvard University,[2] and published after their data was corroborated by Dutch astronomers Muller and Oort,[3] and by Christiansen and Hindman in Australia. After 1952 the first maps of the neutral hydrogen in the Galaxy were made and revealed, for the first time, the spiral structure of the Milky Way.

Uses in radio astronomy Luckily, the spectral line appears within the radio spectrum (in the microwave window to be exact). Electromagnetic energy in this range can easily pass through the Earth's atmosphere and be observed from the Earth with little interference. Assuming that the hydrogen atoms are uniformly distributed throughout the galaxy, each line of sight through the galaxy will reveal a hydrogen line. The only difference between each of these lines is the doppler shift that each of these lines has. Hence, one can calculate the relative speed of each arm of our galaxy. The rotation curve of our galaxy has also been calculated using the 21-cm hydrogen line. It is then possible to use the plot of the rotation curve and the velocity to determine the distance to a certain point within the galaxy. Hydrogen line observations have also been used indirectly to calculate the mass of galaxies, to put limits on any changes over time of the universal gravitational constant and to study dynamics of individual galaxies.

Uses in cosmology The line is of great interest in big bang cosmology because it is the only known way to probe the "dark ages" from recombination to reionization. Including the redshift, this line will be observed at frequencies from 200 MHz to about 9 MHz on Earth. It potentially has two applications. First, by mapping redshifted 21 centimeter radiation it can, in principle, provide a very precise picture of the matter power spectrum in the period after recombination. Second, it can provide a picture of how the universe was reionized, as neutral hydrogen which has been ionized by radiation from stars or quasars will appear as holes in the 21 centimeter background. However, 21 centimeter experiments are very difficult. Ground based experiments to observe the faint signal are plagued by interference from television transmitters and the ionosphere, so they must be very secluded and careful about eliminating interference if they are to succeed. Space based experiments, even on the far side of the moon (which should not receive interference from terrestrial radio signals), have been proposed to compensate for this. Little is known about other effects, such as synchrotron emission and free-free emission on the galaxy. Despite these problems, 21 centimeter observations, along with space-based gravity wave observations, are generally viewed as the next great frontier in observational cosmology, after the cosmic microwave background polarization. Hydrogen line 122

Uses in terrestrial remote sensing The Soil Moisture & Ocean Salinity (SMOS) satellite's main scientific instrument Microwave Imaging Radiometer with Aperture Synthesis (MIRAS) uses the 1400-1427 MHz frequencies (including 1420.406 MHz) to monitor the ocean surface salinity and the soil moisture of the Earth. The choice of HI band results from: 1) much better radiative signature of salinity and moisture in microwave than in higher frequencies, 2) no electromagnetic interference from anthropogenic sources, as HI is reserved for radioastronomy.

Possible uses for SETI The Pioneer plaque, attached to the Pioneer 10 and Pioneer 11 spacecraft, portrays the hyperfine transition of neutral hydrogen and used the wavelength as a standard scale of measurement. For example the height of the woman in the image is displayed as eight times 21 cm, or 168 cm. Similarly the frequency of the hydrogen spin-flip transition was used for a unit of time in a map to Earth included on the Pioneer plaques and also the Voyager 1 and Voyager 2 probes. On this map, the position of the Sun is portrayed relative to 14 pulsars whose rotation period circa 1977 is given as a multiple of the frequency of the hydrogen spin-flip transition. It is theorized by the plaque's creators that an advanced civilization would then be able to use the locations of these pulsars to locate the Solar System at the time the spacecraft were launched. The 21 cm hydrogen line is considered a favorable frequency by the SETI program in their search for signals from potential extraterrestrial civilizations. In 1959, Italian physicist Giuseppe Cocconi and American physicist Philip Morrison published "Searching for Interstellar Communications", a paper proposing the 21 cm hydrogen line and the potential of microwaves in the search for interstellar communications. According to George Basalla, the paper by Cocconi and Morrison "provided a reasonable theoretical basis" for the then nascent SETI program.[4] Pyotr Makovetsky proposed to use for SETI a frequency which is equal to pi times 1420.4 MHz (pi times 1420.40575177 megahertz = 4.46233627 gigahertz; (2 * pi) times 1420.40575177 megahertz = 8.92467255 gigahertz). Since pi is a Transcendental number, such frequency couldn't possibly be produced in a natural way as a harmonic, and would clearly signify its artificial origin. Such signal would not be jammed by HI line itself, or any of its harmonics.[5]

See also • H-alpha, the visible red spectral line with wavelength of 6562.8 Ångstroms • Hydrogen spectral series • Hydrogen Atom • Radio astronomy • Rydberg formula • Spectral line

References

[1] "The Hydrogen 21-cm Line" (http:/ / hyperphysics. phy-astr. gsu. edu/ hbase/ quantum/ h21. html). Hyperphysics. Georgia State University. 2004-10-30. . Retrieved 2008-09-20.

[2] Ewan, H.I.; E.M. Purcell (September 1951). "Observation of a line in the galactic radio spectrum" (http:/ / www. nature. com/ nature/ journal/

v168/ n4270/ pdf/ 168356a0. pdf). Nature 168 (4270): 356. doi:10.1038/168356a0. . Retrieved 2008-09-21.

[3] Muller, C.A.; J.H. Oort (September 1951). "The Interstellar Hydrogen Line at 1,420 Mc./sec., and an Estimate of Galactic Rotation" (http:/ /

www. nature. com/ nature/ journal/ v168/ n4270/ pdf/ 168356a0. pdf). Nature 168 (4270): 357–358. doi:10.1038/168357a0. . Retrieved 2008-09-21. [4] {cite book |last=Basalla |first=George |date=2006 |title=Civilized Life in the Universe |publisher=Oxford University Press |isbn=0195171810 |pages=133–135}}

[5] Makovetsky P. Smotri v koren' (http:/ / n-t. ru/ ri/ mk/ sk109-4. htm) (in Russian) Hydrogen line 123

Cosmology • P. Madau, A. Meiksin and M. J. Rees, "21-cm Tomography of the Intergalactic Medium at High Redshift", Astrophysical Journal 475, 429 (1997) arXiv:astro-ph/9608010. • B. Ciardi, P. Madau, "Probing Beyond the Epoch of Hydrogen Reionization with 21 Centimeter Radiation", Astrophysical Journal 596, 1 (2003) arXiv:astro-ph/0303249. • M. Zaldarriaga, S. Furlanetto and L. Hernquist, "21 Centimeter Fluctuations from Cosmic Gas at High Redshifts", Astrophysical Journal 608, (2004) 608 arXiv:astro-ph/0311514. • X. Chen and J. Miralda-Escudé, "Observing the Reionization Epoch Through 21 Centimeter Radiation", Mon. Not. Roy. Astron. Soc. 347, 187 (2004) arXiv:astro-ph/0303395. • A. Loeb and M. Zaldarriaga, "Measuring the Small-Scale Power Spectrum of Cosmic Density Fluctuations Through 21 cm Tomography Prior to the Epoch of Structure Formation", Phys. Rev. Lett. 92, 211301 (2004) arXiv:astro-ph/0312134. • M. G. Santos, A. Cooray and L. Knox, "Multifrequency analysis of 21 cm fluctuations from the Era of Reionization", Astrophysical Journal 625, 575 (2005) arXiv:astro-ph/0408515. • R. Barkana and A. Loeb, "Detecting the Earliest Galaxies Through Two New Sources of 21cm Fluctuations", Astrophysical Journal 626, 1 (2005) arXiv:astro-ph/0410129.

External links

• The story of Ewen and Purcell's discovery of the 21 cm line (http:/ / www. nrao. edu/ whatisra/ hist_ewenpurcell. shtml)

• Ewen and Purcell's original paper in Nature (http:/ / www. nature. com/ physics/ looking-back/ ewen/ index. html) • PAST experiment, arXiv:astro-ph/0404083.

• LOFAR experiment (http:/ / www. lofar. org/ )

• Mileura Widefield Array experiment (http:/ / web. haystack. mit. edu/ MWA)

• Square Kilometer Array experiment (http:/ / www. skatelescope. org/ ) Hydrogen purity 124 Hydrogen purity

Hydrogen purity or hydrogen quality is a term to describe the lack of impurities in hydrogen as a fuel gas. The purity requirement varies with the application, for example a H ICE can tolerate low hydrogen purity where a 2 hydrogen fuel cell requires high hydrogen purity to prevent catalyst poisoning[1] .

High purity hydrogen In the first generation of fuel cells catalysts like palladium, ruthenium and platinum are used in combination with hydrogen production from hydrocarbons which results in performance degradation. The catalyst poisoning induced by carbon monoxide, formic acid, or formaldehyde can be reversed with a high purity hydrogen stream. Sulfur dioxide is problematic[2]

See also • Glossary of fuel cell terms • Katharometer

References

[1] 2007-DOE-Hydrogen Fuel Quality (http:/ / www. nrel. gov/ docs/ fy07osti/ 41541. pdf)

[2] Issues in hydrogen purity detection and monitoring (http:/ / www. ottawapolicyresearch. ca/ OPRA_Brief_H2PurityDetectionMonitoring. pdf)

External links

• H2 Quality (http:/ / www. fuelcellstandards. com/ H2Quality. ppt)

• 2004-Hydrogen Purity Standard (http:/ / www1. eere. energy. gov/ hydrogenandfuelcells/ pdfs/

fp_workshop_smith. pdf)

• 2004-Fuel Purity Specifications Workshop (http:/ / www1. eere. energy. gov/ hydrogenandfuelcells/ pdfs/

fuel_purity_notes. pdf) Article Sources and Contributors 125 Article Sources and Contributors

Hydrogen Source: http://en.wikipedia.org/w/index.php?oldid=396877701 Contributors: (jarbarf), -- April, -jmac-, 0kdal, 123456mf, 16@r, 65.68.87.xxx, AOC25, AStudent, Abarry, Acerty123, Acroterion, Adambro, Adashiel, Addshore, Adimovk5, Aervanath, Ahoerstemeier, Aitias, Akusarujin, Alexf, AlexiusHoratius, Allstarecho, Alrasheedan, Alsandro, Ancheta Wis, AndreasJS, Andrei Ramanonov, Andres, AndrooUK, Andy M. Wang, Anonymous56789, Antandrus, Anthony Appleyard, Archimerged, Aristophanes68, Aristotle28, Army1987, Arsonal, Ashmedai, Ashmoo, Atelaes, Atlant, Attinio, AvicAWB, AxelBoldt, AySz88, AzaToth, BAZZA42, BBird, BD2412, BRG, Basicdesign, Bcorr, Beetstra, BenFrantzDale, Bender235, Benjamin1414141414141414, Benjamnjoel2, Benji Franklyn, Bensaccount, Bibbidbabbidi, BigBen212, BiggKwell, Blacklemon67, Blahbleh, Blainster, Blimpguy, Blind Man Walking, BlueEarth, Blurpeace, Bobo192, Bongitybongbong, Bookandcoffee, BorgQueen, Borgdylan, Bowei Huang 1, Bpeps, BradBeattie, Brandonrush, Bravehart10000, Brendenhull, Brighterorange, Bryan Derksen, Bsadowski1, Buckyboy314, Bunnyhop11, Buster79, Bù hán ér lì, C'est moi, CStyle, CYD, CalicoCatLover, CambridgeBayWeather, Cameron Nedland, Can't sleep, clown will eat me, Canageek, CaptainVindaloo, Carlobus, Carnildo, Casull, Celarnor, Cerealkiller13, Cfailde, ChaoticLlama, Charles Gaudette, Chemkid1, ChicXulub, Chochopk, Chowbok, Chris Dybala, Chris Henniker, Chrisjj, Chrislk02, Christian75, Christopher Parham, Cimbalom, Civil Engineer III, Clicketyclack, Code E, Colbuckshot, Commander Keane, CommonsDelinker, Condem, Contango, Conversion script, Coppro, Corporal butters, Cosmium, Costyn, Coviekiller5, Crescentnebula, Cryptic, Cryptic C62, Cwkmail, Cybercobra, CyclePat, Cyclotronwiki, Cyrius, D. 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Antihydrogen Source: http://en.wikipedia.org/w/index.php?oldid=396629215 Contributors: 84user, Almightymasteroftheuniverse, Andre Engels, Angr, Antandrus, Astiburg, AxelBoldt, Bambaiah, BenRG, Bob Saint Clar, Bobblewik, CCK, Carlog3, Chronitis, Chrumps, CosineKitty, Curlymeatball38, Dobromila, Domitori, Eclecticology, Enochlau, EoGuy, Eric119, Feezo, Fleminra, Gdr, GeeJo, Headbomb, Heron, Hessamnia, HowardJWilk, Icairns, Idont Havaname, Ihcoyc, Intangir, Jimp, Josh Cherry, Karol Langner, Kieff, Koavf, Korath, Kushal, Kwamikagami, Malcolm Farmer, Marj Tiefert, Massen, Materialscientist, Mike Rosoft, Mion, NClement, Nergaal, Newone, Nuujinn, OMenda, Omegatron, Pedrocelli, Pichote, Pizza1512, Qblik, Revth, Ross Burgess, Rreagan007, SigPig, SkyLined, Smoggyrob, Spacepotato, Terbospeed, Therearewaytoomanybooksinhere, VKokielov, Van helsing, Vortexrealm, Wrightbus, Zachwoo, 43 anonymous edits

Hydrogen atom Source: http://en.wikipedia.org/w/index.php?oldid=396465027 Contributors: 28bytes, 2over0, A. di M., Adamrubin, Addshore, Ahoerstemeier, Akriasas, Antandrus, Anthony Appleyard, Anville, Aquilosion, Army1987, Arnero, Art LaPella, Ashill, AstroNomer, Barbara Shack, BenRG, Bensaccount, BernardH, Bevo, Bgamari, Bkkbrad, BlazerKnight, Bobrayner, Bogey97, Borowsky, Brandonrush, Brownsteve, Bryan Derksen, CYD, Catgut, Chairman S., Charles Matthews, Christopher.Gordon3, Ciaccona, Cometstyles, Complexica, Conversion script, Craig Pemberton, Dainis, Dangermouse29, DarkCatalyst, Dchristle, Discospinster, Donarreiskoffer, Donotresus, Drilnoth, Droidus, DÅ‚ugosz, Eackad, Edsanville, Essjay, Extra999, FlorianMarquardt, Freakofnurture, Geek1337, Gene Nygaard, Geniac, Giftlite, Glenn, Gmeiner, Gogobera, GregRM, Guillom, Guitarstud101, Hadal, HappyCamper, HavikRyan, Headbomb, Homestarmy, Icairns, Invitamia, J.delanoy, JWB, JabberWok, Jaganath, Jared Hunt, Joanjoc, John, John C PI, John254, Josemiotto, Jsalazar, Karol Langner, Keenan Pepper, Kevin Cowtan, Kevmitch, Kickstart70, Kingpin13, KonradG, Korua, Linas, Lincher, Lotje, Lottamiata, Marek69, MathKnight, Mathieu Perrin, Melchoir, Metarhyme, Michael Hardy, Mike40033, Mion, Mlouns, MuDavid, NeonMerlin, Nezzadar, Nilmerg, Njmatulich, Northfox, Oo64eva, Parra22, Passw0rd, Pathfinder, Pfalstad, Picodeoro, Pjacobi, Postscript07, Pyfan, Pérez, Ququ, RDBury, RDLWIK, Res2216firestar, Rgamble, Riana, Robbin' Knowledge, Ronhjones, Rorro, Rory096, Sango123, Sbharris, SeventyThree, Shadowjams, Sikory, Siqamar, Skanaar, Southen, Srleffler, Stephenedie, StewartMH, Stoive, Svick, TUT2006, The Anome, The way, the truth, and the light, Thurth, Tide rolls, Tim Starling, Timwi, Trojancowboy, Ummit, Valodzka, Vanished User 0001, Vaughan Pratt, Vegetator, Vexedd, Vortexrealm, Vsmith, Vsst, WAS 4.250, Wapcaplet, Wayiran, Whiner01, WhiteHatLurker, XJamRastafire, Xanderk84, Zginder, Zmcdargh, Zueignung, Zzuuzz, 225 anonymous edits

Hydrogen-like atom Source: http://en.wikipedia.org/w/index.php?oldid=386237051 Contributors: Achoo5000, Akesich, Barticus88, Bgamari, Chuunen Baka, Dan Gluck, Eequor, Eroica, Feezo, Fresheneesz, Granolanifa, GregRM, HappyCamper, Henrygb, Incnis Mrsi, Iridescent, Itub, Jacopo Werther, Jeppesn, JimR, John C PI, Karol Langner, Linas, Mion, Nergaal, OMCV, Out of Phase User, P.wormer, Paolo.dL, Pecos Joe, Pfalstad, Raghunathan, SPat, Sbandrews, Stereotonic24, Thurth, Trewesterre, Txomin, Xxanthippe, 39 anonymous edits

Hydrogen spectral series Source: http://en.wikipedia.org/w/index.php?oldid=392812384 Contributors: Anna Lincoln, Bender235, DVdm, Dan East, Ducks boy, Headbomb, Karol Langner, Kkmurray, Linas, Marekbrz, Mion, Nergaal, OrangeDog, Papa November, Pearle, R. S. Shaw, RJFJR, Reyk, Sbharris, Srleffler, Starmaker it, Suarez ruibal, Tosqueira, Vsmith, Xager, 凌雲, 45 anonymous edits

Liquid hydrogen Source: http://en.wikipedia.org/w/index.php?oldid=396508382 Contributors: 4RM0, 8472, AGK, Awanta, Badocter, Beaber, Beamjockey, Beetstra, BenFrantzDale, Bird of paradox, Bob Saint Clar, Bryan Derksen, CanOfWorms, Canonymous, CommonsDelinker, Dammit, Edgar181, Enenn, Fangfufu, Frank101, Gene Nygaard, Graham87, Greg L, Grylliade, HalJor, Headbomb, Hibernian, IanOsgood, Iridescent, Isnow, JabberWok, Jaked122, Jaraalbe, Karn, Karol Langner, Keilana, Looxix, MKoltnow, MaBoehm, Materialscientist, Maury Markowitz, Mets501, Michael Hardy, Mike Young, Mion, Monedula, Nergaal, NuclearWarfare, Ojigiri, Oz1sej, Paul August, Phædrus, Pwooster, Quasarstrider, Qurozon, Qwertylex, Rchandra, Rei, Riddley, Rmhermen, Robbin' Knowledge, Samsara, Sergey bloomkin, Shaddack, Shred-69, Stemonitis, Supaman89, The Anome, The Vindictive, Timanderso, Timc, Turbojet, Vadim Makarov, Velella, Article Sources and Contributors 126

Veraladeramanera, Vortexrealm, WAS 4.250, Wikibob, Wikiborg, Wolfkeeper, Woohookitty, 94 anonymous edits

Solid hydrogen Source: http://en.wikipedia.org/w/index.php?oldid=336326340 Contributors: Carcharoth, Mion, Moralis, Nickosaurr, Pstanton, Skier Dude, Stone, Underpants, 2 anonymous edits

Metallic hydrogen Source: http://en.wikipedia.org/w/index.php?oldid=383247016 Contributors: Aerobird, Agd1, Alan Peakall, AndrewBuck, Anthony Appleyard, Ary29, Ase1e1, Ataru, Attilios, Axl, BD2412, Barhamd, Bendzh, Bkell, Bryan Derksen, Calcwatch, Can't sleep, clown will eat me, CarlFeynman, Carlos84, Chemninja, CosineKitty, Crispmuncher, DMacks, Deanlsinclair, Dendropithecus, Doradus, DragonflySixtyseven, DryaUnda, Duncharris, Edgar181, Eleland, Emperorbma, Enochlau, EpiVictor, Fgb, FoeNyx, Fredrik, Gaius Cornelius, GeeJo, Gene Nygaard, Gene.arboit, GeorgeStepanek, Hair Commodore, HalfShadow, Hamiltondaniel, Headbomb, Headcreeps, Hibernian, Houston, Icairns, Igodard, Iknowyourider, Itub, Jaredroberts, Jfromcanada, JimScott, John, Julesd, Karl Andrews, Killing Vector, Kjkolb, Kmarinas86, Kymacpherson, LarryGilbert, Lord Snoeckx, LorenzoB, Lost tourist, LouI, Lovelac7, Mallorn, Materialscientist, Mazarin07, Michael Hardy, Mikeblas, Mikeo, Mion, Modify, Nbishop, Nergaal, Netrapt, Nihiltres, Nonagonal Spider, Novangelis, Objectivist, Ojovan, Omegatron, OrangeDog, Oroso, Pi.C.Noizecehx, Ponder, Quietust, Rich Farmbrough, RobChafer, RodC, Rossami, Salsa Shark, Schueltz 65, ScienceApologist, Serpent-A, Shalom Yechiel, Signalhead, Sinus, Slicky, Smack, Smyth, Stepa, Student1967-68, Swpb, ThAtSo, The Epopt, Thfledrich, Tlogmer, TutterMouse, Variable, Wikipediarules2221, Winiar, XJamRastafire, Youngjim, Zach4636, Zoicon5, 121 anonymous edits

Nascent hydrogen Source: http://en.wikipedia.org/w/index.php?oldid=357113164 Contributors: Abhishek191288, After Midnight, Cryptic C62, Doug butler, DragonflySixtyseven, Georgebts, Headbomb, Kbh3rd, Kku, Mac Davis, Michaf, Mion, Securiger, Shaddack, Shadowjams, Shinkolobwe, SiliconDioxide, Sillybilly, Smokefoot, The way, the truth, and the light, TubularWorld, X42bn6, 14 anonymous edits

Isotopes of hydrogen Source: http://en.wikipedia.org/w/index.php?oldid=396800418 Contributors: (jarbarf), 13mullja, AdjustShift, Ardric47, BiT, Blacklemon67, Blue520, Castorquinn, DabMachine, Daigaku2051, Dirac66, Donarreiskoffer, Driedshroom, EdC, Eric119, Evil Monkey, Femto, Gamer007, Gene Nygaard, Glane23, Greater mind, Headbomb, JFreeman, Jared Preston, John, Julianonions, Karol Langner, Ketiltrout, Killing Vector, Larry R. Holmgren, LeonWhite, Mion, Muro de Aguas, Nergaal, Northfox, Oo64eva, OrangeDog, Oxymoron83, Philip Trueman, PoeticVerse, Pwjb, Retroneo, Reyk, Robbin' Knowledge, Spacepotato, Technopat, Thinking of England, Tide rolls, Tom harrison, V1adis1av, Vossman, Wisdom89, Wsiegmund, Xezbeth, Yerpo, आशीष भटनागर, 102 anonymous edits

Deuterium Source: http://en.wikipedia.org/w/index.php?oldid=395716394 Contributors: 128.59.51.xxx, 130.225.29.xxx, 16@r, 203.109.250.xxx, A2-computist, Adam Conover, Agesworth, Ajaxkroon, An Unknown Person, Andre Engels, Andres, Andrewa, Anthony Appleyard, Ardric47, Ashmoo, AstroHurricane001, Awatral, Bambaiah, Barticus88, Bci2, Ben-Zin, Bender235, Benji9072, Bennish, BiT, BlueNovember, Brandonrush, Brichcja, BrokenSphere, Bryan Derksen, Btg2290, Byrial, C0nanPayne, CABAL, CCooke, Cadwaladr, Can't sleep, clown will eat me, Canderson7, Capricorn42, Ceyockey, Chan Yin Keen, Charles Clark, Chromaticity, Chutznik, Commander Nemet, Comte0, Conversion script, Crazy Fox, CuriousEric, Curps, Cyrek, DMacks, DV8 2XL, Daggerstab, Dan Gluck, DanGarb, Danelo, Davehi1, Deglr6328, Deuterium124, Discospinster, DocWatson42, Dryguy, E23, Edgar181, El C, Elroch, Enric Naval, Epiovesan, Ericwb, F-402, Flying fish, Frank Lofaro Jr., Freestyle-69, Gaius Cornelius, Gekritzl, Gene Nygaard, Geni, Giftlite, Gohmifune, Graham87, Gurch, Gzkn, Hadal, Harp, Hayter, Headbomb, Herbee, HereToHelp, Heron, Icairns, Ilmari Karonen, Infomaxim, JWB, Janke, Jclerman, Jerrykim, John, Juckum, Kainino, Kalamkaar, Karol Langner, Kazvorpal, Kbdank71, Kbh3rd, Kdliss, Keb25, Keenan Pepper, Keepingitfair, Ketiltrout, KhaLduNTR, Killing Vector, Kjkolb, KlaudiuMihaila, Klxmack, Kowey, Kristof vt, Kyle Barbour, LilHelpa, Looxix, Lupinoid, Lupo, Madbehemoth, Madmarigold, Magnus Manske, Malo, ManningBartlett, MarkS, Martianpenguin, Materialscientist, Mav, McSush, Melchoir, Mike40033, Modulatum, MonDroit, Mradigan, Mwoodman, Myasuda, NawlinWiki, Neurolysis, Nick, Nick Y., Nicolokyle, Nihiltres, Nonagonal Spider, OlEnglish, Oli Filth, Oliphaunt, Oo64eva, Oreo Priest, PC THE GREAT, Pakaran, Palica, Panoramix, Parksmp26, Patchouli, Pb30, Phasmatisnox, Phil Boswell, Physchim62, Physicistjedi, PierreAbbat, Piperh, Pjacobi, Pjstewart, ProfessorPaul, Prometheus235, RTC, Raeky, RainbowOfLight, Rebroad, Reyk, Rich Farmbrough, Rjwilmsi, Roadrunner, Rob Mahurin, Roo72, RoryReloaded, RoyBoy, Roycethevoice, Rwflammang, Rydel, SEWilco, SJP, SV Resolution, Salsa Shark, Salsb, Sarastro777, Sbharris, Sbyrnes321, ScAvenger lv, ScienceApologist, Sealpoint33, Securiger, Seth Ilys, Shaddack, Shalom Yechiel, SimonP, SiriusB, SkyLined, Sladen, Smithbrenon, Snigbrook, Spacepotato, Stokerm, Stone, Strait, Surly Dwarf, Takometer, Tapper of spines, Tarquin, Tempshill, That Guy, From That Show!, The ansible, TheTruthiness, Tide rolls, Toddst1, Toligalanis, Tristan Schmelcher, Tsuji, Urhixidur, VASANTH S.N., Vsmith, WFPM, WOSlinker, Warut, Webguy, WestA, WhiteDragon, Whitepaw, Wikisteff, Witan, WriterHound, Xerxes314, Yamaguchi先生, Zeimusu, 253 anonymous edits

Tritium Source: http://en.wikipedia.org/w/index.php?oldid=396546936 Contributors: 128.59.51.xxx, 300840da, ARC Gritt, Aarchiba, Ahoerstemeier, Allissonn, Alvis, An Unknown Person, Andre Engels, Andrejj, Andres, Andrew c, Arbitrarily0, Ardric47, Arman94, Autopilot, Axd, BJ Axel, Bazonka, BlaiseFEgan, BlastOButter42, Bobo192, Borgx, Bornhj, Breakyunit, Bryan Derksen, Cancun771, Capricorn42, Catgut, Cave troll, Cbrown1023, CharlesC, CheekyDreamer, Chyeburashka, Cip25, CipherZero, Conquerist, Conversion script, CosineKitty, DV8 2XL, Danny Miller, Debresser, Deglr6328, Deor, Dfeuer, Dinferno, DiverDave, Dod1, Dr U, Drewzkie, Dricherby, E23, ERcheck, Ebahe4, Edgar181, Eiland, Epbr123, Eric119, FDD, Favonian, Finlay McWalter, FirefoxRocks, Flip 66, Fluzwup, Geni, Georgejmyersjr, Giftlite, Glenn, Graham87, Gypsydoctor, Happy-melon, Hashar, HazyM, Hcberkowitz, Headbomb, Hellbus, HenryLi, Herbee, Heron, Hibernian, HoodedMan, Icairns, IceKarma, Iridescent, Itub, J-Star, J.delanoy, JQF, JWB, JackMcJiggins, Jaganath, Jclerman, Jdforrester, Jimp, JoeBruno, Joelholdsworth, John, JohnDoe0007, JohnOwens, Jon513, Jotomicron, Julesd, KJG2007, KSmrq, Karol Langner, Kay Dekker, Kazvorpal, Kbdank71, Keegan, Keenan Pepper, KlaudiuMihaila, Knotnic, Knute, Kowey, Kwamikagami, Lee Daniel Crocker, Lee J Haywood, Leslie222, LichYoshi, LilHelpa, Looxix, LorenzoB, Luckrider7, Lunch, Mahboud, Malafaya, Malcolm Farmer, Markhurd, Materialscientist, Mattd4u2nv, Megansmith18, Mike Rosoft, Mike40033, Mintrick, Mion, Missy Pentney, Mmeijeri, Nafango2, Nathann sc, Nik42, Nknight, Nonagonal Spider, Novasource, Numbo3, OnePt618, Oo64eva, Open2universe, PJM, Palica, Peter todd, Petri Krohn, Pie4all88, PierreAbbat, Pikazilla, Pinethicket, Polpo, Pstudier, Pwjb, Quadrobyte, Qwertyus, RafaMolina, Rcingham, Rich Farmbrough, Richard Arthur Norton (1958- ), Richards360, Rigosantana3, Ritalib, Rjwilmsi, Ronhjones, Rsquid, Rupertslander, Rursus, Rydel, SB Pete, SCStrikwerda, Sabo, Sam Hocevar, Sbharris, ScAvenger lv, Scog, Scoo, SeanNovack, Sfan00 IMG, Shaddack, Shane Lin, Shimmin, Sjc, SkyLined, Smappy, Smith609, Smurrayinchester, SoM, Spencer, SqueakBox, Stephan Leeds, Stone, Stormwriter, Suisui, Sunborn, SusanLesch, Tarquin, Taxman, Tedmund, The_ansible, Tide rolls, Trelvis, Trevor MacInnis, Tweenk, Tygrrr, Ubern00b, UltimatePyro, Vina, Viralmemesis, Vsmith, Walkinglikeahuricane, Wdsci, Whitepaw, Whitlock, Wiki Phantoms, WikiDao, Wikianon, Wimt, Wlipinski, Ziggaway, Zoidberg, आशीष भटनागर, 329 anonymous edits

Hydrogen-4 Source: http://en.wikipedia.org/w/index.php?oldid=384719175 Contributors: Antonio Lopez, DabMachine, Eric119, Gamer007, Headbomb, Ice Ardor, JWB, John, Karol Langner, Kbdank71, Keenan Pepper, LeonWhite, Mattd4u2nv, Maximaximax, Mewaqua, Mike Rosoft, Mike40033, Oo64eva, OrangeDog, Pamputt, Smith609, Spacepotato, Wang Ivan, 9 anonymous edits

Hydrogen-5 Source: http://en.wikipedia.org/w/index.php?oldid=296211195 Contributors: Ardric47, Bryan Derksen, DabMachine, Eric119, Hellbus, Ice Ardor, JWB, Karol Langner, Kbdank71, Keenan Pepper, Mattd4u2nv, Mike Rosoft, Mike40033, Mike4ty4, Oliphaunt, Oo64eva, Sceptre, Smith609, Spacepotato, Valodzka, 5 anonymous edits

Spin isomers of hydrogen Source: http://en.wikipedia.org/w/index.php?oldid=395497029 Contributors: Aditya.m4, Ascentury, Dirac66, Doradus, Gadolinist, Headbomb, Hellbus, IceKarma, Jaeljojo, Mikespedia, Mion, Nergaal, Opabinia regalis, OrangeDog, Peregrinoerick, SilverStar, Stone, Terrek, Urhixidur, Vertovian, Whiner01, Wolfkeeper, Wyang, Xaa, 22 anonymous edits

Bosch reaction Source: http://en.wikipedia.org/w/index.php?oldid=379704231 Contributors: CharlesC, Chem-awb, Choij, Headbomb, Icer CRO, Marcelo-Silva, Mion, Peter.steier, Silvonen, Tomasz Dolinowski, Treehill, V8rik, ~K, 18 anonymous edits

Hydrogen cycle Source: http://en.wikipedia.org/w/index.php?oldid=379094852 Contributors: 1ForTheMoney, Anxietycello, Atif.t2, Conrad.Irwin, Cpl Syx, Dendlai, Discospinster, Hamburgerman, Headbomb, Jrockley, Karol Langner, Katoa, Keenan Pepper, Michael Hardy, Mikenorton, Onco p53, Orbst, Papodelwiken, Pb30, Poppy, Prashant.ashley, Shrumster, Skiff, Smartse, Snaxe920, Supten, TAS, The Thing That Should Not Be, Vortexrealm, Vsmith, Zawer, 27 anonymous edits

Hydrogenation Source: http://en.wikipedia.org/w/index.php?oldid=396262832 Contributors: 168..., 19vwishart, 2261Daryl, AJim, AThing, Altenmann, AndrewHowse, Antandrus, Beagel, Bensaccount, Biscuittin, Bkell, Borgx, Cacycle, Calmer Waters, Calvero JP, CanadianLinuxUser, CatherineMunro, CerealBabyMilk, Christian75, Christopher Mann McKay, CommonsDelinker, Conortodd, CyclePat, DA3N, DTM, DabMachine, Dante Alighieri, David spector, Edgar181, Effeietsanders, El C, Erbaiwu, Erianna, EtienneCha, Fanghong, FayssalF, Flowchemguy, Forenti, Furrykef, Gareth McCaughan, GenQuest, Gene Nygaard, Gigemag76, Gioto, Guccililpiggy3, Gulliver001, Gökhan, Happyharris, Headbomb, Headius, Hermann Luyken, Hippolyte, Inoculatedcities, Iridescent, Isopropyl, Itub, J.delanoy, J0nokun, Jackfork, Janke, Jimp, Jmendez, Joshuapfohl, Julesd, Karol Langner, Karsten Adam, Kdevans, Keenan Pepper, Kenyon, Kostisl, LOL, LeadSongDog, Leslie Mateus, Loupeter, Lovecz, MER-C, MMS2013, Mausy5043, Mbeychok, Mdf, Michael Hardy, Mion, Mitchan, Mmmsnouts, Müslimix, NJA, Nevit, Nirvana2013, Notreallydavid, Novickas, OrangeDog, OverlordQ, PaperTruths, Physchim62, Picus viridis, Pinethicket, Poor Yorick, Qaddosh, RazorICE, RealGrouchy, RedHillian, Rhadamante, RickyWiki, SeventyThree, Shadow Puppet, Shawnc, Skittleys, Smokefoot, Soliloquial, Soyseñorsnibbles, Spalding, Stephenb, Stone, Tabledhote, Takometer, Tarotcards, Taurrandir, The Anome, The 189 ,لیقع فشاک ,MoUsY spell-checker, Tides, Trackbar, Turnstep, Tyciol, Tyler, V8rik, Vortexrealm, Vuo, Whosasking, Wimvandorst, Wjsams, Woohookitty, Wspencer11, Ww, ~K anonymous edits

Dehydrogenation Source: http://en.wikipedia.org/w/index.php?oldid=395537881 Contributors: Bob, Bobo192, Carlog3, Craptree, Edgar181, Fermi121, Ideal gas equation, Itub, Jmendez, Keenan Pepper, Mion, Nirmos, Rifleman 82, Smaljers, Vortexrealm, 15 anonymous edits

Transfer hydrogenation Source: http://en.wikipedia.org/w/index.php?oldid=396153470 Contributors: Andrewpmk, Beagel, Keenan Pepper, Mion, Nuklear, OMCV, Smokefoot, Stone, Takometer, V8rik, Vortexrealm, 10 anonymous edits

Hydrogenolysis Source: http://en.wikipedia.org/w/index.php?oldid=376574197 Contributors: Adkins, CatherineMunro, Edgar181, Gnostic804, Kostisl, Mion, Nseidm1, Rifleman 82, Seansheep, Smokefoot, Stone, Tonyrex, Unara, V8rik, Vortexrealm, Vuo, Zotel, ~K, 5 anonymous edits Article Sources and Contributors 127

Hydron Source: http://en.wikipedia.org/w/index.php?oldid=381012749 Contributors: Armando-Martin, Chotu21, December21st2012Freak, Firq, Itub, Julianonions, Mikespedia, Okedem, Puppy8800, Reindra, Rifleman 82, Stone, Whiner01, Wickey-nl, 9 anonymous edits

Sabatier reaction Source: http://en.wikipedia.org/w/index.php?oldid=391814198 Contributors: Antaeus Feldspar, Benjamindees, BiggKwell, Ceyockey, Charles Matthews, DanPope, Dlchambers, DonSiano, Headbomb, Itub, Jamelan, Ken g6, Leonard G., Like tears in rain, Mac, Marcelo-Silva, Mion, NickFr, Okedem, Onco p53, PigFlu Oink, Prari, Proximo.xv, Richcon, Sbandrews, Sdsds, Sillybilly, Toytoy, Ufinne, Vortexrealm, Who, 28 anonymous edits

Hydrogen damage Source: http://en.wikipedia.org/w/index.php?oldid=393031210 Contributors: Bleh999, Craig Pemberton, Eastlaw, Edward, Element16, FCYTravis, Hkhenson, John, John anonymous edits 13 ,یکیو یلع ,Quiggin, Julesd, Mion, Peruvianllama, Portrino, Saimhe, Shaddack, Tkgnamboodhiri, Vortexrealm, Wildstar2501, Wizard191

Hydrogen embrittlement Source: http://en.wikipedia.org/w/index.php?oldid=395705728 Contributors: Abc root, Afroozpromethe, Anonymousphrase, Antiuser, Bernd in Japan, Craig Pemberton, DRRLRA, Dagordon01, Diberri, DragonflySixtyseven, Eastlaw, Elektron, Element16, Equinox2, EricWesBrown, Fosnez, Gaius Cornelius, George Burgess, Gigemag76, Headbomb, Hooperbloob, Iain.mcclatchie, John, Ksuresh10, L.Raymond&Associates, LRA-FDI-RSL, LorenzoB, Mackay64, Michael Frind, Mikiemike, Mion, Orphan Wiki, Physchem, Radagast83, Rei, 51 ,یکیو یلع ,Rhun, Rudyh01, Shaddack, Snezzy, StaticGull, Stephenb, TheNewPhobia, Tkgnamboodhiri, Trisino, Turboragtop, Vortexrealm, Vsmith, Wavelength, Wizard191, ZorbaTHut anonymous edits

Hydrogen leak testing Source: http://en.wikipedia.org/w/index.php?oldid=351505588 Contributors: Aardvarktesting, Cgarber, FayssalF, Headbomb, Lambdacore, Maseracing, Mion, Nergaal, Quantumobserver, Trentool2, Vortexrealm, 11 anonymous edits

Hydrogen safety Source: http://en.wikipedia.org/w/index.php?oldid=395812143 Contributors: Iridescent, Jjhamilton, Mion, Nergaal, NuclearWarfare, Pbspbs, R'n'B, Rei, Robbin' Knowledge, Sergey bloomkin, Shoefly, Tkma, Xenonice, 8 anonymous edits

Timeline of hydrogen technologies Source: http://en.wikipedia.org/w/index.php?oldid=393572682 Contributors: Cromwellt, Daniel Christensen, FiggyBee, Gerhard51, Giovanni-P, Headbomb, Hibernian, Kingdon, Mild Bill Hiccup, Mion, Nergaal, OrangeDog, Ospalh, Wolfkeeper, 18 anonymous edits

Biohydrogen Source: http://en.wikipedia.org/w/index.php?oldid=393581157 Contributors: 3l1t1st, Appeltree1, C777, ChildofMidnight, Dancter, Erud, Freewaay, Gmohanakrishna, Gobonobo, Green caterpillar, Headbomb, Hebrides, IstvanWolf, Jerome Charles Potts, KVDP, Kasjens, Mac, MarsInSVG, Mild Bill Hiccup, Mion, Mirgy, Morphriz, Nergaal, Rich Farmbrough, Rosenbluh, SebastianHelm, Smokefoot, Terjepetersen, Vortexrealm, Welsh, 22 anonymous edits

Hydrogen production Source: http://en.wikipedia.org/w/index.php?oldid=396126029 Contributors: ABF, Aaadddaaammm, Acdx, Alagiah, Alan Liefting, Alansohn, AlexH555, AndrewBuck, Appeltree1, Armadillo1985, Ashmoo, Awotter, Balrog-kun, Barneca, Beagel, Behun, Bill W Ca, BlindEagle, Bobamnertiopsis, Bobblewik, CalumH93, CambridgeBayWeather, Casimirpo, Chem prof2000, Chris G, Closedmouth, CyclePat, Echo-cycle, Ehines99, Environnement2100, Equendil, EverGreg, Eyckfreymann, Eyrian, Falcon8765, FellGleaming, Gaius Cornelius, Green caterpillar, Headbomb, Heron, Htomfields, Inwind, Iridescent, JForget, JHunterJ, Jandre680, Jerome Charles Potts, Jorfer, KVDP, Kaldosh, Klixovann, Koppas, L Kensington, LilHelpa, Loren.wilton, Margin1522, Materialscientist, Matrix452, Mattisse, Mbeychok, Megiddo1013, Mets501, MgW, Mion, MonoViejo, Mrz1818, NJGW, Nergaal, Nick2588, Nikolai Eroshenko, Nseidm1, OMCV, Olthebol, Petlif, Phantom25, Pinethicket, Pingpongpan, Pjacobi, Pserfass, Pstudier, Quasarstrider, RJHall, Robbin' Knowledge, Rocketere o1, SD5, Sbharris, Sequoian, Sergey bloomkin, Shaddack, Simesa, Skier Dude, Smokefoot, Ssilvers, Stan J Klimas, Stanislao Avogadro, Student050608, SudlonrA, SyntaxError55, Timberframe, Trekphiler, Virgofenix, Vortexrealm, Voyevoda, Vsmith, Wavelength, WereSpielChequers, Wikicali00, Woohookitty, Wtshymanski, Wwoods, 136 anonymous edits

Hydrogen infrastructure Source: http://en.wikipedia.org/w/index.php?oldid=389491417 Contributors: Appeltree1, Daduck08, Geologyguy, Gregory Dziedzic, Headbomb, Hmains, KVDP, Mion, Nergaal, OrangeDog, RFerreira, Sergey bloomkin, Skierpage, Supaman89, 2 anonymous edits

Hydrogen line Source: http://en.wikipedia.org/w/index.php?oldid=396203548 Contributors: 0xFFFF, 84user, Adaminstalbans, Binksternet, Bowlhover, Camouflage55, CapitalR, Charles Matthews, Chekaz, Christopherlin, Commdor, Curps, DJIndica, Daveliney, Dina, Dmmaus, Eyreland, Gabodon, Giftlite, Gmaxwell, GregorB, Gurch, HairyDan, Headbomb, Hetar, Husond, II MusLiM HyBRiD II, IRP, Iridescent, J.delanoy, JabberWok, Jacek Kendysz, Joke137, KJS77, Kaldosh, Karol Langner, Krash, Kvng, METIfan, Mcleodm, MichaelVernonDavis, Mike Peel, Mion, Mushin, Nergaal, Oliverkeenan, One-dimensional Tangent, OrangeDog, PhatSmurf, Phe, Phorse, Pjacobi, RJHall, RayTomes, Rykul, SDC, Sam Hocevar, Samw, Shortbread, Sirhulio, Smalljim, Spiderfrog, Steve Pucci, Stwalkerster, Sverdrup, THF, Ta bu shi da yu, Thingg, TimBentley, Tubbs334, Uhjoebilly, Viriditas, Vortexrealm, Zandperl, Zzuuzz, Δζ, 68 anonymous edits

Hydrogen purity Source: http://en.wikipedia.org/w/index.php?oldid=372569471 Contributors: Benjah-bmm27, Mion, 1 anonymous edits Image Sources, Licenses and Contributors 128 Image Sources, Licenses and Contributors

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