The determination of kinetics parameters of the hydrogen evolution on Ti-Ni alloys by ac impedance

The kinetics and mechanism of hydrogen evolution at Ti-Ni alloys electrode has been studied by means of steady-state potentiostatic polarization and ac impedance spectrum measurements. Complex-plane spectrum plots are derived for the h.e.r. at one of the most inactive, typical hydridic, Ti-Ni, and one of the most active, typical electrocatalytic, Ti-Ni-3, intermetallic alloy compounds at various potentials. The rate constants of the forward and backward reactions of the corresponding steps were estimated by a nonlinear fitting method. It has been found that the overall reaction proceeds through a coupled Volmer-Heyrovsky mechanism. The electrocatalytic activity decreases in the order TiNi2 > TiNi3 > TiNi4 > Ti2Ni > TiNi > Ti3Ni > TiNi0.7