Effect of C14 Laves/BCC on microstructure and hydrogen storage properties of (Ti32.5V27.5Zr7.5Nb32.5) 1-xFex (x = 0.03, 0.06, 0.09) high entropy hydrogen storage alloys

Abstract

In order to explore the effect of C14 Laves/BCC on the hydrogen storage properties of high entropy hydrogen storage alloys, (Ti32.5V27.5Zr7.5Nb32.5) 1-xFex (x = 0.03, 0.06, 0.09) high entropy hydrogen storage alloys are prepared. The C14 Laves/BCC rises with the increase of Fe content. The C14 Laves phase provides a path for the diffusion of hydrogen atoms, so that defects with higher hydrogen binding energy capture more hydrogen atoms to ensure the increase of initial hydrogen absorption content in the activation process. The appropriate ratio of C14 Laves/BCC ensures that the main hydrogen absorbing phase BCC phase of high entropy hydrogen storage alloy plays a full role. The (Ti32.5V27.5Zr7.5Nb32.5) 0.94Fe0.06 high entropy hydrogen storage alloy possesses the best hydrogen absorption capacity of 3.19 wt% at 150 °C under 3 MPa hydrogen pressure. The gradual increase of Fe content makes the VEC value of C14 Laves phase rise, so that the hydrogen binding energy decreases. The factor reduces the thermal stability of metal hydrides. The reversible phase transition of BCC phase + metal C14 Laves phase → FCC phase + metal hydride C14 Laves phase → BCC phase + metal C14 Laves phase occurs in the whole cycle.