Electrocatalysis for hydrogen evolution reaction on nickel-hydrogen storage alloy composite electrodes prepared by electrodeposition

Nickel-rare earth hydrogen storage alloy (Ni-AB₅5) composite electrodes were prepared by the electrodeposition technique, and their electrocatalytic characteristics for hydrogen evolution reaction (HER) in 28% KOH solution were investigated by steady-state polarization curves and electrochemical impedance spectroscopy (EIS). The morphology of the electrodes was examined by using scanning electron microscopy (SEM). The experimental results show that in comparison with those of the electrodes electrodeposited with pure Ni, the Ni-AB₅ composite electrodes exhibit a lower overpotential and reaction resistance, a higher exchange current density and specific surface area for HER. The standard free activation enthalpy of HER on the pure-Ni and Ni-AB₅ electrodes is 74.2 kJ/mol and 39.8 kJ/mol respectively. Thus the Ni-AB₅ composite electrodes possess a superior electrocatalytic activity for HER as related to the pure-Ni electrodes. The main pathway for HER on the Ni-AB₅ composite electrodes in alkaline solutions is Volmer-Heyrovsky with the electrochemical desorption as the rate-determining step.