XRD study of the hydrogenation and dehydrogenation process of the two different phase components in a Ti–V-based multiphase hydrogen storage electrode alloy

Hydrogenation and dehydrogenation of two different phases in a multiphase Ti–V-based alloy Ti_0.8Zr_0.2V_1.867Mn_0.373Cr_0.56Ni_0.7, namely the C14 Laves phase with hexagonal structure and the V-based solid solution phase with body centered cubic (bcc) structure during electrochemical charging and discharging were investigated by X-ray powder diffraction (XRD) analysis. For the alloy investigated, the C14 Laves phase component, which had good surface electrochemical activity for decomposing water, was hydrogenated from the very beginning of the charging process and was providing hydrogen to both phase components throughout the entire electrochemical charging process. The V-based solid solution phase, which had no or very low surface electrochemical activity for decomposing water during electrochemical charging, could obtain hydrogen only from its neighboring C14 Laves phase component when the hydrogen content of which was high enough to build up an adequate pressure to feed hydrogen to its neighboring phase component. The V-based solid solution phase experienced a phase change when the hydrogen in it reached a definite level, namely from bcc to body centered tetragonal (bct) structure. Probably due to the high stability of bct hydride phase of the V-based solid solution phase, it did not revert back to the initial bcc structure during the electrochemical discharging process conducted in our experiment at the room temperature and atmospheric pressure.