Electrochemical hydrogenation and dehydrogenation mechanisms of the Ti-V base multiphase hydrogen storage electrode alloy

The electrochemical hydrogenation and dehydrogenation mechanisms of a multiphase Ti-V base alloy Ti_0.8Zr_0.2V_1.867 Mn_0.373Cr_0.56Ni_0.7 have been studied by XRD Rietveld analyses, based on the linear relationship between the volume expansion and charging capacity. The results show that the as-cast alloy is composed of a C14 Laves phase with hexagonal structure and a V base solid solution phase with bcc structure. During electrochemical charging, the unit cell volume expansion (ΔV/V) of the Laves phase is from 0.301% to 2.719% and for the bcc phase from 0.011% to 1.685% for the charging durations from 3.33 min to 120 min, respectively. During electrochemical discharging (ΔV/V) of the Laves phase decreases from 14.542% to 8.119% and for the bcc phase from 8.117% to 6.248% for the discharging durations from 0 min to 165 min, respectively. Therefore, during electrochemical charging, the Laves phase was hydrogenated from very beginning of the charging process. The bcc phase could obtain hydrogen only from its neighboring Laves phase. The electrochemical discharging mechanism is similar to that of charging. In conclusion, C14 Laves phase and V base solid solution phase are the hydrogen storage phases with high hydrogen storage capacities in the alloy Ti_0.8Zr_0.2V_1.867 Mn_0.373Cr_0.56Ni_0.7; C14 Laves phase also works as an electrochemical catalyst for the V base solid solution phase, which enhances the use of V base solid solution phase to make electrochemical properties of Ti-V base multiphase hydrogen storage electrode alloys preferable.