Microstructural features and improved reversible hydrogen storage properties of ZrTiVFe high-entropy alloy via Cu alloying

Abstract

ZrTiVFe high-entropy alloy has shown desirable hydrogen absorption and desorption properties due to its lattice distortion effect and high content of C14 phase that can store hydrogen. In this study, element Cu was used to improve the reversible hydrogen storage properties of equimolar ZrTiVFe alloy by increasing valence-electron concentration (VEC), and (ZrTiVFe)1-xCux (x = 0.05, 0.1, 0.2) alloys were prepared. After studying their microstructural features and hydrogen storage properties, the results indicate that (ZrTiVFe)0.95Cu0.05 and (ZrTiVFe)0.90Cu0.10 alloys are mainly consisted of C14 Laves phase and a small amount of α-Ti and α-Zr phases. When the Cu content increases to 20 at. %, the microstructure transforms to reticular ZrTiCu2 phase around C14 Laves phase, and the Cu8Zr3 phase is formed in final solidification stage. The fastest hydrogen absorption rate of (ZrTiVFe)0.80Cu0.20 alloy at room temperature suggests the ZrTiCu2 and Cu8Zr3 phases can provide preferential paths for hydrogen atoms diffusion. The amount of hydrogen in (ZrTiVFe)0.90Cu0.10 hydride that cannot be desorbed at 400 °C in vacuum is greatly reduced from 0.370 wt% to 0.084 wt% comparing with ZrTiVFe hydride. The addition of element Cu reduces the stability of ZrTiVFe hydride significantly, which favors the hydrogen desorption of the (ZrTiVFe)1-xCux alloys.