Modification of nano-eutectic structure and the relation on hydrogen storage properties: A novel Ti–V–Zr medium entropy alloy

TiV-based alloys present desirable hydrogen storage properties owing to the formation of Body-centered cubic (BCC) solid solutions. However, the nanostructure that helps hydrogen absorption and desorption is hard to be designed and prepared in these alloys. In this study, Ti40Zr60-xVx (x = 20, 25, 30) alloys with hyperfine nano-eutectic structures of 50–500 nm in lamellar space are prepared, and the nano-eutectic structures can be refined by increasing Zr content. Ti40Zr60-xVx alloy powder exhibits excellent activation and hydrogenation properties. The phase separation and nano-eutectic structure are formed due to the differences of atomic size in Ti40Zr60-xVx alloys. The highest total hydrogenation capacity of 2.4 wt% is obtained within 10 min at 200 °C under 1 MPa H2 by Ti40V35Zr25 alloy, surpassing that of Ti40Zr40V20 and Ti40Zr30V30 alloys of 2.2 wt% in 20min. Based on the Johnson-Mehl-Avrami-Kolmogorov (JMAK) model, lower energy is required for the hydrogenation of Ti40V35Zr25 alloy. Due to the formation of some stable hydrides, the Ti40Zr60-xVx alloys show lower reversible hydrogenation capacities. The spinodal decomposition in Ti40V35Zr25 alloy facilitates the formation of reticular eutectics, which provide high-density phase interfaces and produce “synergistic effect”. As a result, the hydrogenation kinetic and capacity are enhanced significantly.