Compositionally complex doping for low-V Ti-Cr-V hydrogen storage alloys

Ti-V-based BCC solid solution alloys, represented by Ti-Cr-V alloys, are considered as promising hydrogen storage materials due to their high hydrogen storage capacity (over 4 wt%) at room temperature. However, the difficult activation, low effective hydrogen desorption capacities, poor P-C-T plateau characteristics, and high cost remain significant problems for their practical applications. Herein, we present a new compositionally complex (high-entropy) doping strategy which was used to successfully fabricate a low-cost "Laves phase related BCC solid solution", TiCrV0.7(Nb0.2Fe0.2Co0.2Ni0.2Mn0.2)0.2, that exhibits excellent activation performance and high effective hydrogen desorption capacity (Ce1atm: 2.21 wt%). The main BCC phase ensures high hydrogen storage capacity, while the minor secondary C14 phase plays a catalytic role and thus improves the hydrogen absorption kinetics. Furthermore, we confirmed that there is a synergistic effect of Nb, Fe, Co, Ni, and Mn elements in improving hydrogen storage performance. The dehydrogenation enthalpy ΔH of the heat-treated TiCrV0.7(Nb0.2Fe0.2Co0.2Ni0.2Mn0.2)0.2 is 37.5 kJ mol−1, which is significantly lower than previously reported Ti-Cr-V based systems, revealing a significant tendency towards easier dehydrogenation with high-entropy doping. This work offers a new alloying method for improving the hydrogen storage performance of hydrogen storage alloys.