Kinetics and electrocatalytic behavior of nanocrystalline CoNiFe alloy in hydrogen evolution reaction

Electrocatalytic activity of electrodeposited nanocrystalline CoNiFe alloy in hydrogen evolution reaction (HER) was studied in 1 M NaOH solution. The steady-state polarization measurement and electrochemical impedance spectroscopy were used to determine the Tafel slope, the exchange current density and the activation energy. The simulation of the data obtained from these two methods, using a nonlinear fitting procedure, allowed us to determine the surface coverage and the rate constants associated with the mentioned reaction. The ac-impedance spectra measured at various overpotentials in the HER region exhibited three semicircles in the complex plane plots. The high-frequency semicircle was attributed to the electrode geometry, whereas the intermediate and low frequency semicircles were due to the electrode kinetics. The results also demonstrated that CoNiFe alloy possessed slightly higher specific electrocatalytic activity than Ni itself. Nevertheless, the contribution of high specific surface area of nanocrystalline alloy in hydrogen evolution was by far more significant. The effects of temperature and poisoning on the electrochemical parameters were also studied.