Electrocatalytic activity of nickel-based coatings deposited in DES-assisted plating baths containing cerium(III) ions

This paper concerns electrodeposition of coatings from electrolytes containing NiCl2 (0.1 mol dm–3) and CeCl3 (0.1–0.4 mol dm–3) salts dissolved in a deep eutectic solvent, ethaline (ethylene glycol+choline chloride). The electrochemical deposition was carried out at cathodic current densities from 1 to 5 mA cm–2 and temperatures from 50 to 900C. It was shown that micromodification of the chemical composition of coatings with cerium occurred (no more than ~1–2.65 wt.% Ce), and the content of cerium in the coating was increased with an increase in the concentration of the Ce(III) salt in the plating electrolyte, an increase in the current density, and a decrease in the temperature. It was shown for the first time that the Ni-based electrodeposits micromodified with cerium exhibited an enhanced electrocatalytic activity in the reaction of hydrogen evolution in an alkaline medium (a decrease in the cathodic polarization by ~200–250 mV). Electrocatalytic activity correlated with the content of cerium in the coating. The enhancement of the efficiency of electrocatalysis resulting from micromodification of the chemical composition of the coatings with cerium was explained within the framework of the well-known concept of the synergistic effect of hypo-hyper-d-electronic combinations of transition metals. The use of electrolytes based on deep eutectic solvents provides additional opportunities for flexible control of the composition of deposited coatings and their electrocatalytic behavior via changes in the concentration of electrolyte components and electrolysis conditions in relatively wide intervals.