| Abstract
| - Alloying with Si is shown to destabilize the strongly bound hydrides LiH and MgH2. For the LiH/Si system,a Li2.35Si alloy forms upon dehydrogenation, causing the equilibrium hydrogen pressure at 490 °C to increasefrom approximately 5 × 10-5 to 1 bar. For the MgH2/Si system, Mg2Si forms upon dehydrogenation, causingthe equilibrium pressure at 300 °C to increase from 1.8 to >7.5 bar. Thermodynamic calculations indicateequilibrium pressures of 1 bar at approximately 20 °C and 100 bar at approximately 150 °C. These conditionsindicate that the MgH2/Si system, which has a hydrogen capacity of 5.0 wt %, could be practical for hydrogenstorage at reduced temperatures. The LiH/Si system is reversible and can be cycled without degradation.Absorption/desorption isotherms, obtained at 400−500 °C, exhibited two distinct flat plateaus with littlehysteresis. The plateaus correspond to formation and decomposition of various Li silicides. The MgH2/Sisystem was not readily reversible. Hydrogenation of Mg2Si appears to be kinetically limited because of therelatively low temperature, <150 °C, required for hydrogenation at 100 bar. These two alloy systems showhow hydride destabilization through alloy formation upon dehydrogenation can be used to design and controlequilibrium pressures of strongly bound hydrides.
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