Electrochemical preparation and characteristics of Ni–Co–LaNi5 composite coatings as electrode materials for hydrogen evolution

Electrocatalytic activity for the hydrogen evolution reaction on Ni–Co–LaNi5 composite electrodes prepared by electrochemical codeposition technique was evaluated. The relationship between the current density for hydrogen evolution reaction and the amount of LaNi5 particles in Ni–Co baths is like the well-known “volcano plot”. The Surface morphology and microstructure of Ni–Co–LaNi5 coatings were determined by means of scanning electron microscopy (SEM) and X-ray diffraction (XRD). The kinetic parameters were determined from electrochemical steady-state Tafel polarization and electrochemical impedance spectroscopy technology in 1 M NaOH solution. The values obtained for the apparent energies of activation are 32.48, 46.29 and 57.03 kJ mol−1 for the Ni–Co–LaNi5, Ni–Co and Ni electrodes, respectively. The hydrogen evolution reaction on Ni–Co–LaNi5 proceeds via Volmer–Tafel reaction route with the mixed rate determining characteristics. The composite coating Ni–Co–LaNi5 is catalytically more active than Ni and Ni–Co electrodes due to the increase in its real surface areas and the decrease in the apparent free energy of activation caused by the electrocatalytic synergistic effect of the Ni–Co alloys and the hydrogen storage intermetallic particles on the electrode surface. © 2003 Elsevier B.V. All rights reserved.