Increasing de-/hydriding capacity and equilibrium pressure by designing non-stoichiometry in Al-substituted YFe2 compounds

Non-stoichiometric YFe1.5Al0.5-x, YFe1.6Al0.4-x and YFe1.7+xAl0.3 (x = 0.1 and 0.2) compounds with single C15 Laves phase were successfully prepared. Compared with stoichiometric compounds, enhanced hydrogenation capacity and hydrogen absorption rate were obtained in hypo-stoichiometric compounds, and increased dehydrogenation equilibrium pressure was achieved for hyper-stoichiometric compounds. The YFe1.6Al0.2 compound shows the maximum reversible absorption capacity of 3.04 H/f.u. (1.63 wt.%), which is 18% higher than that of YFe1.5Al0.5. Faster hydrogenation kinetics could be obtained in all of the hypo-stoichiometric samples, completing hydrogenation within 300 s at 100 °C. The YFe1.7+xAl0.3 compounds showed elevated desorption equilibrium pressure, indicating higher dehydrogenation capacity than that of stoichiometric compounds. The present work demonstrates the positive effect of non-stoichiometry on the Y-Fe-Al ternary compounds and plays a guiding role for improving the hydrogen storage properties of AB2-type rare earth-transition metal alloys.