Electrochemical Charge for the Formation of Metal Hydrides from LiH+M (M=Mg, Al)
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1216-W08-24
Electrochemical charge for the formation of metal hydrides from LiH+M (M = Mg, Al) Nobuko Hanada1, Akito Kamura1, Hiroshi Suzuki1, Takayuki Ichikawa2, Yoshitsugu Kojima2 and Kenichi Takai1 1 Department of Engineering and Applied Sciences, Sophia University, 7-1 Kioi-cho, Chiyoda-ku, Tokyo, 102-8554, Japan. 2 Institute for Advanced Materials Research, Hiroshima University, 1-3-1 Kagamiyama, HigashiHiroshima, 739-8530, Japan ABSTRACT For a formation of metal hydride of MgH2 or AlH3 under room temperature and ambient pressure, the cathode electrodes of metal and lithium hydride are electrochemically charged with Li anode electrodes in the system of Li-ion extraction. For MgH2 formation, the VC (VoltageComposition) curve of Mg + 2LiH during charge shows a plateau voltage at 0.6 V until the final composition of 1.05 Li extraction. After charging MgH2 phase is observed by the XRD measurement. Therefore MgH2 is produced by the electrochemical charge from Mg and LiH. For AlH3 formation, Al + 3LiH is charged until the final composition of 0.6 Li at a plateau voltage of 0.8 V which corresponds to the reaction between Al and LiH for the formation of AlH3. In the XRD profile after charging AlH3 phase is not detected although the intensities of Al and LiH decrease compared with these before charging, which suggests the reaction leading to the formation of AlH3. INTRODUCTION In order to use hydrogen as an alternative energy source in mobile applications, hydrogen storage in solid medium is considered as one of the most promising options instead of compressed hydrogen gas or liquid hydrogen. Among considered hydrogen storage materials, aluminum hydride is one of the most promising candidate because it possesses high hydrogen capacity of 10.1 mass% and low hydrogen desorption temperature of 150 °C1-3. However, because the enthalpy of the formation of AlH3 is small −7.6 kJ/molH24, an equilibrium H2 fugacity for the formation of AlH3 from Al and hydrogen molecules is 26 GPa (equivalent to 0.6 GPa H2 pressure) at 298 K5. The direct hydrogenation of Al is reported under both high pressure and temperature 8.9 GPa and 600 °C6. But the typical formation route is through the chemical reaction of lithium alanate with aluminum chloride in diethyl ether7. Furthermore Zidan et al. have recently synthesized AlH3 electrochemically, providing a synthetic route which closes a reversible cycle from cathode material of Al plate and electrolyte of THF and sodium alanate8. In the Li-ion battery system, extensive works have been performed towards improvement of anode electrodes, cathode electrodes and electrolytes in order to obtain a battery with higher capacity9. For the anode electrodes, alloys10, oxides11 and carbons have been investigated to overcome the limit of the capacity of the currently used graphite of 372 mAh/g9,12. Oumellal et al. have investigated the metal hydride of MgH2 as an anode electrode13-14. The MgH2 electrode shows a large, reversible capacity of 1,480 mAh/g at an average voltage of 0.5 V versus Li+/Li. It is point
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