Structural, thermodynamic and kinetic factors in the desorption/absorption of a hydrogen molecule in the M3AlH10−xNa (M = Be or Mg; x = 0 or 2) hydrides

Abstract

In the context of the design and study of new materials for hydrogen storage, in this work structural, compositional, thermodynamic and kinetic-mechanistic factors for the desorption/absorption of a hydrogen molecule in the M₃AlH_10−xNa (M = Be or Mg; x = 0 or 2) hydrides are evaluated. The results show that the mechanisms of hydrogen detachment/attachment are energetically more favorable when the two involved hydrogen atoms are related to different metals in each system. The hydrogenation of M₃AlH₈Na occurs very easily at relatively low temperatures. The most convenient values of temperature and rate constants for thermal dehydrogenation are reached for the Be₃AlH₁₀Na system in tetrahedral geometry. These factors, together with the fact that this structure is quite symmetrical, make the tetrahedral Be₃AlH₁₀Na a good candidate as an assembly unit for suprastructures. However, our results indicate that the dehydrogenation temperature is rather high; so, future studies about ways to facilitate Be₃AlH₁₀Na dehydrogenation, such as its catalysis or its support on some surface, are necessary for energy-based uses.