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Hydrogen Storage Overview HYDROGEN STORAGE (Materials) Arturo Fernandez Madrigal Instituto de Energias Renovables-UNAM [email protected] Questions ¿what is the state of the art on hydrogen as energy storage? ¿Which are the main challenges of involved technologies? Hydrogen Economic Hydrogen and other fuels [Sørensen, 2005]. Propiedad Hidrógeno Metanol Metano Propano Gasolina Unidad Mínima energía de 0.02 ---- 0.29 0.25 0.24 mJ ignición Temperatura de 2045 ---- 1875 ---- 2200 °C flama Temperatura de 585 385 540 510 230-500 °C autoignición Máxima velocidad 3.46 ---- 0.43 0.47 ---- m/s de flama Rango de 4-75 7-36 5-15 2.5-9.3 1.0-7.6 Vol. % flamabildad Rango de 13-65 ---- 6.3-13.5 ---- 1.1-3.3 Vol. % explosividad Coeficiente de 0.61 0.16 0.20 0.10 0.05 10-3 m2/s difusión Energy Content of Comparative Fuels Physical storage of H2 •Compressed •Metal Hydride (“sponge”) •Cryogenically liquified •Carbon nanofibers Chemical storage of hydrogen •Sodium borohydride •Methanol •Ammonia •Alkali metal hydrides New emerging methods •Amminex tablets •Solar Zinc production •DADB (predicted) •Alkali metal hydride slurry Compressed •Volumetrically and Gravimetrically inefficient, but the technology is simple, so by far the most common in small to medium sized applications. •3500, 5000, 10,000 psi variants. Liquid (Cryogenic) •Compressed, chilled, filtered, condensed •Boils at 22K (-251 C). •Slow “waste” evaporation •Gravimetrically and volumetrically efficient •Kept at 1 atm or just slightly over. but very costly to compress 9 Metal Hydrides (sponge) •Sold by “Interpower” in Germany •Filled with “HYDRALLOY” E60/0 (TiFeH2) •Technically a chemical reaction, but acts like a physical storage method •Hydrogen is absorbed like in a sponge. •Operates at 3-30 atm, much lower than 200-700 for compressed gas tanks •Comparatively very heavy, but with good volumetric efficiency, good for small storage, or where weight doesn’t matter Carbon Nanofibers Complex structure presents a large surface area for hydrogen to “dissolve” into Early claim set the 2 standard of 65 kgH2/m and 6.5 % by weight as a “goal to beat” The claim turned out not to be repeatable Research continues… Methanol Broken down by reformer, yields CO, CO2, and H2 gas. Very common hydrogen transport method Distribution infrastructure exists – same as gasoline Ammonia Slightly higher volumetric efficiency than methanol Must be catalyzed at 800-900 deg. C for hydrogen release Toxic Usually transported as a liquid, at 8 atm. Some Ammonia remains in the catalyzed hydrogen stream, forming salts in PEM cells that destroy the cells Many drawbacks, thus Methanol considered to be a better solution Alkali Metal Hydrides “Powerball” company, makes small (3 mm) coated NaH spheres. “Spheres cut and exposed to water as needed” H2 gas released Produces hydroxide solution waste Sodium Borohydrate Sodium Borohydrate is the most popular of many hydrate solutions Solution passed through a catalyst to release H2 Commonly a one-way process (sodium metaborate must be returned if recycling is desired.) Some alternative hydrates are too expensive or toxic The “Millennium Cell” company uses Sodium Borohydrate technology Amminex •Essentially an Ammonia storage method •Ammonia stored in a salt matrix, very stable •Ammonia separated & catalyzed for use •Likely to have non-catalyzed ammonia in hydrogen stream •Ammonia poisoning contraindicates use with PEM fuel cells, but compatible with alkaline fuel cells. Amminex •High density, but relies on ammonia production for fuel. •Represents an improvement on ammonia storage, which still must be catalyzed. •Ammonia process still problematic. Diammoniate of Diborane (DADB) So far, just a computer simulation. Compound discovered via exploration of Nitrogen/Boron/Hydrogen compounds (i.e. similar to Ammonia Borane) Thermodynamic properties point towards spontaneous hydrogen re-uptake – would make DADB reusable (vs. other borohydrates) Solar Zinc production Zinc powder can be easily transported Zinc can be combined with water to produce H2 Alternatively could be CeMIESol-Proyecto 10. “Combustibles made into Zinc-Air Solares y Procesos Industriales” (COSOLπ). batteries (at higher •Objetivo: Investigación y desarrollo en la utilización de energía solar para el energy efficiency) desarrollo sustentable de procesos termoquímicos, producción de combustibles límipos y valorización de materiales empleados en la industria nacional. Alkaline metal hydride slurry SafeHydrogen, LLC Concept proven with Lithium Hydride, now working on magnesium hydride slurry Like a “PowerBall” slurry Hydroxide slurry to be re-collected to be “recycled” Competitive efficiency to Liquid H2 On Board Hydrogen Storage Targets were set by the FreedomCAR Partnership in January 2002 between the United States Council for Automotive Research (USCAR) and U.S. DOE (Targets assume a 5-kg H2 storage system). The 2005 targets were not reached in 2005. The targets were revised in 2009 to reflect new data on system efficiencies obtained from fleets of test cars. The ultimate goal for volumetric storage is still above the theoretical density of liquid hydrogen. It is important to note that these targets are for the hydrogen storage system, not the hydrogen storage material. System densities are often around half those of the working material, thus while a material may store 6 wt % H2, a working system using that material may only achieve 3 wt % when the weight of tanks, temperature and pressure control equipment, etc., is considered. In 2010, only two storage technologies were identified as being susceptible to meet DOE targets: MOF-177 exceeds 2010 target for volumetric capacity, while cryo-compressed H2 exceeds more restrictive 2015 targets for both gravimetric and volumetric capacity). 21 Storage Method Comparison Method Gravimetric storage Volumetric mass (in kg) Comments efficiency (% mass H2) of H2 per litre High pressure in cylinders 0.7-3.0 0.015 Widely used Metal Hydride 0.65 0.028 Suitable for small systems Cryogenic liquid 14.2 0.040 Widely used for bulk storage Methanol 6.9 0.020 Low cost chemical Sodium Hydride 2.2 0.036 Problem of disposing of spent solutions NaBH4 solution in water 3.35 1.0 Very expense to run Sodium hydride slurry 0.9 1 Must reclaim used slurry DABD 0.1-0.2 0.09-0.1 (numbers for plain “diborane”and sodium borohydride, should be similar) Amminex 9.1 0.081 US-DOE goal 9.0 0.81 What Are the Challenges? Hydrogen has a very high energy content by weight (about 3 times more than gasoline), but it has a very low energy content by volume (liquid hydrogen is about 4 times less than gasoline). This makes hydrogen a challenge to store, particularly within the size and weight constraints of a vehicle. A light-duty fuel cell vehicle will carry approximately 4-10 kg of hydrogen on board (depending on the size and type of the vehicle) to allow a driving range of more than 300 mi, which is generally regarded as the minimum for widespread public acceptance. Drivers must also be able to refuel at a rate comparable to the rate of refueling today’s gasoline vehicles. Using currently available high-pressure tank storage technology, placing a sufficient quantity of hydrogen onboard a vehicle to provide a 300-mile driving range would require a very large tank — larger than the trunk of a typical automobile. Aside from the loss of cargo space, there would also be the added weight of the tank(s), which could reduce fuel economy. Low-cost materials and components for hydrogen storage systems are needed, along with low-cost, high-volume manufacturing methods for those materials and components. Hydrogen can be stored on the surfaces of solids by adsorption. In adsorption, hydrogen associates with the surface of a material either as hydrogen molecules (H2) or hydrogen atoms (H). This figure depicts hydrogen adsorption within MOF-74. 23 Storage Hydrogen (Metal Hydride) Some metals and metal alloys have the property of forming reversible covalent bonds when they react with hydrogen. Metal Hydride can store hydrogen by adsorb-desorb cycles. Metal hydrides carry a proportion of 1-7% by weight of hydrogen. More than 200 different alloys have been studied being. The metal transition group are more suitable. Metal hydrides requires high temperatures (300-350ºC) to release hydrogen. Metal Hydride stored at pressures between 3 and 6 MPa Contin……… M + nH2 → M-H2n + heat (absorption) M-H2n + heat → M + nH2 (desorption) M represents the metal, element or alloy. The one of the major problem of the metal- hydride tanks is necessary the addition energy to recover the hydrogen Hydride storage systems are becoming a very safe way to store hydrogen in domestic applications . Fuels and Storage energy Storage of 3 kg Storage of 10 storage density H2 (360 MJ) kg de H2 (1200MJ) MJ/kg MJ/l kg l kg l Gasoline 43 32 8.3 11.3 28 37.5 H2 liq. 120 8.5 3 42.3 10 141 FeTiH 1.80 3 200 84 665 280 MgH2 8.73 7.85 41.3 46 138 153 http://hcc.hanwha.co.kr/english/pro/ren_hsto_idx.jsp 27 Targets for On-Board Hydrogen Storage 28 Metal-organic frameworks (MOFs) Metal-organic frameworks represent another class of synthetic porous materials that store hydrogen and energy at the molecular level. MOFs are highly crystalline inorganic-organic hybrid structures that contain metal clusters or ions (secondary building units) as nodes and organic ligands as linkers. When guest molecules (solvent) occupying the pores are removed during solvent exchange and heating under vacuum, porous structure of MOFs can be achieved without destabilizing the frame and hydrogen molecules will be adsorbed onto the surface of the pores by physisorption. Compared to traditional zeolites and porous carbon materials, MOFs have very high number of pores and surface area which allow higher hydrogen uptake in a given volume. The, research interests on hydrogen storage in MOFs have been growing since 2003 when the first MOF-based hydrogen storage was introduced.
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