Kinetics of hydrogen evolution reaction on nanocrystalline electrodeposited Ni62Fe35C3 cathode in alkaline solution by electrochemical impedance spectroscopy

Ternary nickel–iron–carbon (Ni–Fe–C) alloys have been characterized by means of microstructural and electrochemical techniques in view of their possible applications as electrocatalytic materials for hydrogen evolution reaction (HER). The electrochemical efficiency of the electrodes has been evaluated on the basis of electrochemical data obtained from the steady-state polarization Tafel curves, electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) in 1 M NaOH solution at 298 K in the absence and presence of cyanide ion as the poison. Steady-state polarization Tafel curves showed that the Ni–Fe–C electrodes were apparently active for the HER. Therefore, the EIS studies were performed to obtain more precise data and find the source of activity. A surface roughness of more than three orders of magnitude was observed for Ni62Fe35C3 electrode. The rate constants of the forward and backward reactions of Volmer and Heyrovský steps were estimated by using Tafel-impedance data. A comparison between the values obtained for Rf by the EIS and the values obtained for k2 by approximation of Tafel-impedance data revealed that the increase in activity of Ni62Fe35C3 electrode toward the HER was partially (20%) originated from increase in the surface roughness, and mostly (80%) from increase in the intrinsic activity.