Microstructural evolution and hydrogen storage performance of TiZrHfVNb1-xCux (for X = 0, 0.6, 0.8 and 1) high-entropy alloys

Abstract

High-entropy alloys (HEAs), particularly those with body-centered cubic (BCC) and C14-laves structures, have gained attention for their tunable hydrogen storage properties. This study investigates the TiZrHfVNb_1-xCu_x system, focusing on the impact of incremental Nb substitution by Cu (x = 0.6, 0.8, and 1.0) on microstructural evolution and hydrogen absorption behavior. The introduction of Cu leads to phase segregation, with V enrichment in dendrites and Zr/Hf accumulation in interdendritic regions, promoting a mixed BCC and C14 Laves phase structure. The increase in Cu content facilitates the formation of C14 Laves phases because Cu, being a relatively small atom, effectively satisfies the geometrical criterion necessary for the stabilization of this phase when substituting Nb. Initial hydrogenation performed at room temperature reveals that the HEAs achieve a hydrogen storage capacity of 1.4–1.6 wt% with rapid kinetics following thermal activation. Notably, the TiZrHfVCu alloy (x = 1) exhibits reversible hydrogen absorption and desorption near atmospheric pressure, storing 1.5 wt% hydrogen. These findings underscore the TiZrHfVNb_1-xCu_x system's potential for hydrogen storage under accessible temperature and pressure conditions, suggesting a pathway to viable solid-state hydrogen storage applications.