Electrodeposition of coatings from urea-choline chloride-based plating baths containing Ni(II) and Ce(III) chloride salts and electrocatalytic activity of electrodeposits towards the hydrogen evolution reaction

An electrolyte based on the deep eutectic solvent reline (a mixture of choline chloride and urea) was used for electrodeposition of coatings containing nickel and cerium. It was shown that a decrease in temperature and an increase in the concentration of cerium(III) ions in the plating bath lead to an increase in the content of cerium in the electrodeposits. Under certain conditions of electrolysis, it was possible to prepare coatings that contain nanocrystalline nickel with the inclusion of up to 40-59 wt.% cerium. The kinetics and reaction mechanism of hydrogen evolution on electrodeposited coatings in an aqueous alkaline medium of 1 M NaOH were studied in detail using the methods of Tafel analysis and electrochemical impedance spectroscopy. It was stated that a significant increase in the electrocatalytic activity of the electrodeposited material is observed with an increase in the content of cerium in the coating. A possible mechanism of the process (Volmer-Heyrovsky reaction pathway) was proposed and equivalent circuits were developed that adequately describes the registered impedance hodographs. A comparison of the results obtained in this work with literature data showed that the coating fabricated in reline-based electrolytes exhibit a higher content of cerium, and therefore a higher electrocatalytic activity towards the hydrogen evolution reaction than coatings produced from electrolytes based on ethaline (a eutectic mixture of choline chloride and ethylene glycol).