Investigation of the kinetics and mechanism of the hydrogen evolution reaction on copper

In this study, the effects of temperature, solution pH, and hydrogen pressure on the kinetics of the hydrogen electrode reaction (HER) on copper in borate buffer solution have been studied by means of steady-state polarization measurements, including electrochemical impedance spectroscopy (EIS). In order to obtain electrokinetic parameters, such as the exchange current density and the cathodic Tafel slope, two stages of optimization have been performed. From the optimization process, the activation energy (E_ac) of theHER on copper was obtained as ≈ 32 kJ mol^-1. Moreover, the mechanism of hydrogen evolution reaction (HER) on copper in mildly alkaline media has been studied by means of EIS over the frequency range of 0.01 Hz ≤ f ≤ 5 kHz. The impedance spectra were modeled using a mechanism based upon the Volmer-Heyrovsky-Tafel steps for hydrogen evolution and by considering the reactions involved in hydrogen atom and hydroxyl group adsorption on the copper surface. A single set of kinetic parameters, including the rate constants and transfer coefficient, has been derived for each pH by optimization of the mechanistic model on the experimental impedance (eis) data. It is postulated that the HER proceeds through the Volmer-Heyrovsky-Tafel mechanism with the Volmer reaction being the rate-determining step.