Copper–nickel alloy as a potential electrocatalyst for oxygen evolution and urea oxidation reactions: effect of anodic treatment in deep eutectic solvents

An experimental study was conducted to investigate the effects of anodic treatment of a copper–nickel alloy (~55 wt.% Cu) in deep eutectic solvents (DESі) on its electrocatalytic behavior in the oxygen evolution reaction and electrochemical urea oxidation reaction in an aqueous alkaline medium of 1 M NaOH. The chosen DES mixtures were eutectic mixtures of choline chloride with ethylene glycol and urea (ethaline and reline, respectively). Anodic treatment was performed in potentiostatic mode for 2.5 hours at potentials of 0.3, 0.5, 0.7, 1.0, 1.35, and 1.7 V relative to a silver quasi-reference electrode. Linear voltammetry revealed that anodic treatment of the copper–nickel alloy in either ethaline or reline at any of the applied potentials results in an increase in the polarization of oxygen evolution reaction. In the case of urea oxidation reaction, an increase in current density, indicating enhanced electrocatalytic activity, was observed at specific anodic treatment potentials. The specific nature of the surface treatment's effect on the Cu–Ni alloy in different DES and the non-monotonic influence of anodic treatment potential on electrocatalytic activity in both the oxygen evolution and electrochemical urea oxidation reactions in an alkaline medium were attributed to changes in surface morphology. These morphological changes lead to corresponding alterations in the nature, concentration, and activity of catalytic sites involved in the studied reactions. The results of this work may contribute to the development of processes for the electrolytic synthesis of green hydrogen via water electrolysis, where the oxygen evolution is replaced with urea oxidation reaction.