Application of urea-based deep eutectic solvent for electrodeposition of copper selenide (Cu2−xSe/CuSe) electrocatalyst for hydrogen evolution reaction in acidic medium

This work presents a simple method for copper selenide electrodeposition on carbon substrate using electrolyte based on a ‘reline’ deep eutectic solvent (choline chloride + urea). A detailed adjustment of the electrodeposition process is presented, including solvent selection, effects of applied potential, duration, and annealing conditions. The materials were characterized using SEM, EDS, XRD, XPS, and Raman. EDS results show that as-synthesized materials contain 60–66 at.% Cu and 34–40 at.% Se, while annealed under optimal conditions (200 °C) exhibit 60–61 at.% Cu. The annealed Cu-Se materials show also morphological changes and crystallinity. XRD of the annealed electrodes indicated the presence of a mixture of $Cu_{2−x}Se$ (cubic $Cu_{1.8}$Se) and hexagonal CuSe phases. The selected materials were tested for $H_{2}$ evolution activity in 0.5 M $H_{2}SO_{4}$, indicating a significant reduction in the HER overpotential of about 120 mV (@10 mA $cm^{−2}$) and 240 mV (@100 mA $cm^{−2}$) compared to carbon substrate. Our work demonstrates also a significant change in the Tafel slope from 169 mV $dec^{−1}$ for the substrate to 43–53 mV $dec^{−1}$ for copper selenide electrodes. This work is the first to highlight the application potential of copper selenide electrodeposited from a DES reline-based electrolyte for the HER in an acidic medium.