Electrocatalytic Activity of the Ni57.3Co42.7 Alloy for the Hydrogen Evolution

The hydrogen evolution reaction (HER) on Ni57.3Co42.7 alloy and its main components, polycrystalline nickel and cobalt was investigated in 1.0 mol L-1 NaOH solution at 20 degrees C using cyclic voltammetry, pseudo-steady-state linear polarization and electrochemical impedance spectroscopy methods. The purpose of investigation was to evaluate the effect of cobalt on the intrinsic catalytic activity of nickel. Cyclic voltammetry measurements, performed in a wide potential range from hydrogen to oxygen evolution, clearly showed the potential range of formation and reduction metal oxides / hydroxides. Electrocatalytic activity of the investigated electrodes was derived from pseudo-steadystate linear polarization curves, Tafel plots and electrochemical impedance spectroscopy (EIS). Electrochemical impedance spectra obtained in potential range of hydrogen evolution were modeled with modified Randles electric equivalent circuit. Kinetic parameters (the exchange current density and the cathodic Tafel slope), determined from linear polarization measurements and electrochemical impedance measurements, were compared for all three electrode materials. Ni57.3Co42.7 catalyst has shown better electrocatalytic activity compared with pure Co. The main pathway for the HER at investigated electrode materials is Volmer-Heyrovski with Heyrovsky as the rate determining step.