Comparative study of Ga and Al alloying with ZrFe2 for high-pressure hydrogen storage

Abstract

ZrFe2 reacts reversibly with hydrogen under extremely high hydrogen pressure and shows potential for high-pressure hydrogen compression and storage. Alloying is indispensable to tune its hydrogen storage properties for practical applications. Previous works indicated that the Al substitution for Fe would drastically decrease hydrogen storage capacity. This work used the quenching process to prepare the ZrFe2-xAlx and ZrFe2-xGax (0.1 ≤ x ≤ 0.2) alloys with a single C15 Laves phase structure. It was found that the presence of the second phase Zr2Fe in as-cast alloys is responsible for the capacity reduction. The quenched ZrFe1.9Al0.1 alloy delivers a maximum hydrogen storage capacity of 1.79 wt%, much higher than as-cast alloys. The comparative study further shows that ZrFe2-xGax alloys have a relatively higher equilibrium pressure than ZrFe2-xAlx alloys due to a higher bulk modulus for ZrFe2-xGax alloys by the theoretical calculations. The hydrogen storage performance test indicates that the hydrogen dissociation pressure of ZrFe1.9Ga0.1 and ZrFe1.9Al0.1 is 164.0 atm and 130.7 atm at 298 K, respectively. Our work demonstrates that ZrFe2-based alloys with a small Ga or Al substitution are suitable for high-pressure hydrogen storage applications.