Studies on hydrogen storage properties of TiVFeNi, (TiVFeNi)95Zr5 and (TiVFeNi)90Zr10 high entropy alloys

Abstract

The major issues associated with High Entropy Alloys (HEAs) as hydrogen storage material are the activation of these alloys and low storage capacity. The aim of the present investigation is to reduce the activation process and increase the hydrogen storage capacity of TiVFeNi-based HEAs. We investigated the effect of different Zr content on the hydrogen storage properties of TiVFeNi-based HEAs. Four different Ti25V25Fe25Ni25, (TiVFeNi)95Zr5, (TiVFeNi)90Zr10, and (TiVFeNi)80Zr20 HEAs were synthesized through mechanical alloying. The as-synthesized Ti25V25Fe25Ni25 alloy possessed a mixture of bcc and fcc phases. However, the as-synthesized (TiVFeNi)95Zr5 and (TiVFeNi)90Zr10 HEAs possessed bcc and fcc phases with a ZrFe2 intermetallic phase. We found that as the Zr content increases, alloys' hydrogenation behavior, improves due to the better activation process. Among the studied HEAs, in present studies, the highest hydrogen storage capacity is found to be 2.86 wt% at RT with 10 atm of hydrogen pressure for (TiVFeNi)90Zr10 HEA after 15 activation cycles at different temperatures. The high absorption value was found due to the formation of intermetallic ZrFe2, which acts as a bridging entity on the surface of the synthesized bcc and fcc phases. The present study provides a detailed insight into how the presence of the ZrFe2 phase reduces the activation process as well as enhances the hydrogenation properties of TiVFeNi-based HEAs.