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Light-Metal Hydrides for Hydrogen Storage

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Light-Metal Hydrides for Hydrogen Storage !" #$%# "$ % $ &'(' '&&') *$+%* ! "#"$$%$&#' ' '( )* + , ) !-)"$$%).- ' ! )/ ) 000)#0 ) )%12.%.##3.1#2#.1) ' 4 . + 5 ' + ) 6 ' ' + )- ' +' )! ' ' ))-* /)* + ' + ) - 71)0 +)8 9 ' -": + 4 '' + '' ). + ' ' + ' ' + ) ; . )* '' + + ) * + 4 <. + '' + '' ) = + ) -.>. ' -" . ) 6 -")* ' ' 4 : + ' >")!/.- ' ' )= ' !" /7-9 ' ) = + '!" 3$$?@ + ) -. <. '' '' !" ! !# $%&'! !()*%+,+ ! A- !"$$% =!!B0#.0"3 =!CB%12.%.##3.1#2#.1 & &&& .$1D2$7 &EE )6)E F G & &&& .$1D2$9 Publications included in this thesis This thesis is a summary of the following publications, referred to in the text by their Roman numerals: I Hydrogen desorption studies of the Mg24Y5-H system: Formation of Mg tubes, kinetics and cycling effects C. Zlotea, M. Sahlberg, S. Oezbilen, P. Moretto and Y. Andersson. Acta Materialia, 56 (2008) 2421-2428 II Hydrogen absorption in Ti doped Mg24Y5 C. Zlotea, M. Sahlberg, P. Moretto and Y. Andersson Journal of Alloys and Compounds, In submission III YMgGa M. Sahlberg, T. Gustafsson and Y. Andersson Acta Crystallographica, E63 (2007) i195 IV YMgGa as a hydrogen storage compound M. Sahlberg, C. Zlotea, P. Moretto and Y. Andersson Journal of Solid State Chemistry, 182 (2009) 1833-1837 V Hydrogen absorption in Mg-Y-Zn ternary compounds M. Sahlberg and Y. Andersson Journal of Alloys and Compounds, 446-447 (2007) 134-137 VI Sc2MgGa2 and Y2MgGa2 M. Sahlberg and Y. Andersson Acta Crystallographica, C65 (2009) i7-i8 VII A new material for hydrogen storage, ScAl0.8Mg0.2 M. Sahlberg, P. Beran, T. Kollin Nielsen, Y. Cerenius, K. Kadas, M.P.J. Punkkinen, L. Vitos, O. Eriksson, T.R. Jensen and Y. An- dersson Accepted for publication in Journal of Solid State Chemistry VIII Fully reversible hydrogen absorption and desorption reactions with Sc(Al1-xMgx), x = 0.0, 0.15, 0.20 M. Sahlberg, C. Zlotea, M. Latroche and Y. Andersson In manuscript Reprints were made with permission from the publishers. My contributions to paper I-VIII I Synthesis of the samples, XRD, part of writing. II Synthesis of the samples, XRD, part of writing. III Major part of the experimental work and the writing. IV Major part of the experimental work, part of PCT and TDS, first author. V Major part of the experimental work and the writing. VI Major part of the experimental work and the writing. VII Major part of the experimental work, first author. VIII Major part of the experimental work and the writing. Contents 1. Introduction...............................................................................................11 2. The scope of this thesis.............................................................................14 3. Metal hydrides as hydrogen storage materials..........................................15 3.1 Complexes..........................................................................................16 3.2 Alloys .................................................................................................16 3.2.1 Alloys with yttrium and magnesium...........................................17 3.2.2 Alloys with scandium and magnesium .......................................18 4. Experimental.............................................................................................19 4.1 Material synthesis...............................................................................19 4.2 Hydrogen absorption..........................................................................20 4.2.1 High pressure synthesis ..............................................................20 4.2.2 Deuterium absorption .................................................................21 4.3 Diffraction ..........................................................................................21 4.3.1 X-ray powder and single crystal diffraction ...............................21 4.3.2 Synchrotron radiation X-ray powder diffraction ........................22 4.3.3 Neutron powder diffraction ........................................................22 4.3.4 Crystal structure determination and refinement..........................23 4.4 Absorption / desorption isotherms and thermal desorption spectroscopy.............................................................................................23 4.5 Microstructural analysis .....................................................................25 4.6 Thermal analysis ................................................................................25 4.7 Density functional theory calculations...............................................26 5 Y-Mg-based alloys.....................................................................................27 5.1 Mg24Y5................................................................................................27 5.1.1 Mg24Y5-Ti ...................................................................................28 5.2 YMgGa...............................................................................................30 5.3 Mg3Y2Zn3 ...........................................................................................34 5.4 Summary of the Y-Mg-based alloys ..................................................35 6 Sc-Mg-based alloys....................................................................................37 6.1 Sc2MgGa2 ...........................................................................................37 6.2 Sc(Al1-xMgx), x 0.2..........................................................................38 6.2.1 ScAl0.8Mg0.2 ................................................................................38 6.2.2 Sc(Al1-xMgx), x 0.20 ................................................................44 6.3 Summary of the Sc-Mg-based alloys .................................................47 7. Concluding remarks..................................................................................48 7.1 Parameters influencing hydrogen storage properties .........................48 7.2 Synthesis of new materials.................................................................48 Acknowledgements.......................................................................................50 Summary in Swedish ....................................................................................51 References.....................................................................................................54 Abbreviations DFT Density functional theory DTA Differential thermal analysis EDS Energy dispersive X-ray spectros- copy EMTO Exact muffin-tin orbitals GGA Generalized gradient approximation HDDR Hydrogenation-disproportionation- desorption-recombination NPD Neutron powder diffraction SEM Scanning electron microscopy SR-XRD Synchrotron radiation X-ray powder diffraction TEM Transmission electron microscopy TDS Thermal desorption spectroscopy TG Thermal gravimetry TM Transition metal TPD Temperature programmed desorption UHV Ultra-high vacuum XRD X-ray diffraction 1. Introduction The greenhouse effect has been a major political issue during the last years. There has also been a global effort to reduce the emission of carbon dioxide in the atmosphere, even though there is still a very long way to go. These issues have led to an increasing interest for clean energy systems and vehi- cles with no emission of greenhouse gases1,2. For the zero emission vehicle idea to be realized a new way to store en- ergy must be used. There are two main groups of zero-emission energy car- riers that are being considered for automotive applications, batteries and hydrogen2. Batteries have the advantage that you only need an electric outlet in order to “refuel” your vehicle. However, the amount of energy that can be stored in today’s batteries is limited, leading to a practical limit of the driving range of the vehicle. The battery charging time is also too long, usually more than 4 hours. When hydrogen reacts with oxygen, water is formed and energy is re- leased, as described below. The released energy can be used to power a ve- hicle with water as the rest product. There are two ways to use the energy in hydrogen: by burning the hydrogen and get the energy as heat or by reac- tions with oxygen in a fuel cell, to form electricity. There are two key advan- tages with using a hydrogen powered fuel cell vehicle instead of a normal gasoline powered vehicle: the total “well-to-wheels” energy efficiency in- creases by a factor of three3 and there is no emission of greenhouse gases. H2 + ½O2 H2O + energy There are many different ways to produce hydrogen4. Renewable energy can be used to produce hydrogen, such as photovoltaic hydrogen generation that include light generated electricity and water splitting5. Another way is to use microorganisms like green algae that produce hydrogen under anaerobic conditions6. However, most hydrogen produced today comes from reforming natural gas, oil or coal3. The chemical energy per mass in hydrogen, 142 MJ/kg, is very high compared to today’s fuels. A completely clean energy system is achieved if renewable energy is used to produce hydrogen gas, as described in Figure 1.1. 11 Figure 1.1. The hydrogen energy cycle. Hydrogen powered vehicles usually have a longer driving
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