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 1M NaOH solution. The values obtained for the apparent energies of activation are 32.48, 46.29 and 57.03kJmol^-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.