Electrocatalytic behavior of the codeposited Ni-Co-LaNi₅ coatings for hydrogen evolution in alkaline medium

Composite coatings of Ni-Co-LaNi₅, prepared by electrolytic codepositon of Ni-Co alloys and LaNi₅ particles from a sulfamate electrolyte were investigated in view of its possible application as electrocatalytic materials for the hydrogen evolution reaction(HER). The surface morphology and microstructure of Ni-Co-LaNi₅ coatings were observed by means of SEM and XRD. Electrocatalytic efficiency was evaluated on the basis of electrochemical steady-state Tafel polarization and electrochemical impedance spectroscopy technology in 1mol·L^-1 NaOH solution. The results were compared with Ni-Co and Ni electrodes. The real electrochemical area was estimated by apparent double-layer capacitances to account for the large difference in roughness factor of the three surfaces. The values obtained for the apparent energy of activation were 32.48kJ· mol^-1, 46.29kJ·mol^-1 and 57.03kJ·mol ^-1 for the HER on the Ni-Co-LaNi₅, Ni-Co and Ni electrodes, respectively. The composite coatings 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 energy of activation caused by electrocatalytic synergistic effect of the Ni-Co alloy and the rare-earth compound on the electrode surface.