Kinetics of hydrogen evolution reaction on hydrogen storage alloy electrode in alkaline solution and effects of surface modification on the electrocatalytic activity for hydrogen evolution reaction

The kinetics of the hydrogen evolution reaction (HER) of the hydrogen storage alloy electrode (MmNi3.6Co0.7Mn0.4Al0.3) were investigated by Tafel polarization curves. The results of Tafel polarization curves showed that the HER on the metal hydride (MH) electrode was Volmer–Tafel route, in which the electron transfer on the MH electrode surface was a rate-determining step. The electrocatalytic activity of the MH electrode for the HER was greatly improved by immersing the hydrogen storage alloy electrode in a hot alkaline solution containing KBH4. After surface modification, the exchange current density for HER of MH electrode was observably increased, and the apparent activation energy of HER was decreased from 35.6 kJ mol−1 for untreated MH electrode to 29.4 kJ mol−1 for MH electrode treated in a hot 6 M KOH solution, and to 22.7 kJ mol−1 for MH electrode treated in a hot 6 M KOH containing 0.05 M KBH4. The Ni-rich layer on the alloy surface was produced and the specific surface area of the alloy was augmented after the surface modification, hence leading to the enhancement of the adsorption of the hydrogen atom on the alloy surface, which being the intermediate for HER. These facts were the main reasons for the improvement in the electrocatalytic activity for HER on the MH electrode.