The Zr element promotes the BCC phase separation in Ti_20-xV₂₅Cr₃₀Nb₂₅Zr_x (x = 4, 6, 8, 10, 12) high-entropy alloys to enhance the hydrogen desorption performance

This study investigates the effects of Zr substitution for Ti on microstructure and hydrogen storage properties in Ti_20-xV₂₅Cr₃₀Nb₂₅Zr_x (x = 4, 6, 8, 10, 12) high-entropy alloys (HEAs). The gradual substitution of Zr for Ti changes the phase ratio of the HEAs, resulting in a decrease in the BCC phase content and an increase in the C15 Laves phase content. Therefore, hydrogen absorption capacity exhibits an inverse relationship with Zr content. Hydrogen absorption capacity of Ti₈V₂₅Cr₃₀Nb₂₅Zr₁₂ decreased by 50 % compared with 2.10 wt.% of Ti₁₆V₂₅Cr₃₀Nb₂₅Zr₄ at 323 K. However, the hydrogen desorption capacity shows a trend of decreasing first and then increasing. The hydrogen desorption capacity of Ti₁₂V₂₅Cr₃₀Nb₂₅Zr₈ is 16 % higher than that of Ti₁₄V₂₅Cr₃₀Nb₂₅Zr₆ alloy at 323 K. The BCC2 phase in Ti₁₂V₂₅Cr₃₀Nb₂₅Zr₈ alloy exhibits a larger lattice constant than the BCC1 phase. Therefore, the existence of the BCC2 phase benefits the desorption of H atoms and enhances the dehydrogenation performance of HEAs. This indicates that the increase of Zr content leads to the change of phase composition in HEAs, which increases the number of phase boundaries, enhancing the dehydrogenation performance of the HEAs. These findings provide a reference for the composition design of hydrogen storage HEAs.