Effect of alloys modified by sodium borohydride alkaline solutions on the kinetics of hydrogen evolution reaction at Mm(Ni3.6Co0.7Mn0.4Al0.3)1.15 hydride electrodes

The effects of treating the alloy powder of an electrode with 6 M sodium hydroxide solution containing y M (y = 0.0, 0.005, 0.01, 0.02, 0.03, 0.05) sodium borohydride (NaBH4) on the kinetics of hydrogen evolution reaction (HER) at the Mm(B5)1.15 hydride electrode (Mm = cerium-rich mischmetal; B5 = Ni3.6Co0.7Mn0.4Al0.3) are described. Several kinetic parameters are considered, including Total, Volmer and Tafel overpotentials, exchange current densities and activation energies of the elementary reactions. Such parameters are investigated by measuring the overpotential decay immediately after the interruption of an applied cathodic current. The effects of NaBH4 treatment and temperature on the mechanism of the HER are analysed on the basis of the dependence of the Volmer and Tafel overpotentials on current density. The effect of the NaBH4 concentration on the performance of the hydrogen storage alloy as a negative electrode material in nickel-metal hydride batteries and/or alkaline fuel cells is discussed from the standpoint of relative velocity of the elementary reactions.