Improvement of Mg–Al alloys for hydrogen storage applications

Abstract

In the context of energy carrier, storage of hydrogen is one of the key challenges for research today. The group of Mg-based hydrides stands as a promising candidate for competitive hydrogen storage with high reversible hydrogen capacity. The present studies report encouraging results for Mg–Al system with Nb 2O 5 additive catalyst. Three nominal compositions [(Mg x Al 100− x )−99 + (Nb 2O 5)−1 mol.%], X = 100 (Mg), X = 39 ( β-Mg 2Al 3) and X = 70 (Mg + γ-Mg 17Al 12) have been investigated for their hydrogen equilibrium pressure of absorption and desorption reactions, from 250 °C to 400 °C. Decomposition of initial Nb 2O 5 phase was shown after long annealing of samples, with reduction into other oxides. Moreover, the hydrogenation of Mg–Al alloys leads to separate initial phase(s) through several stages with the formation of MgH 2 hydride and metallic Al-fcc as the final products. This behavior is clearly visible from multi-plateaux of pressure–composition isotherm curves. In the case of the X = 70 compound, the reaction was accomplished through three reversible transformation steps. The hydrogen weight capacity of 4.7 wt.% has been found at 250 °C under reproducible conditions.