<p>Many high-entropy oxides exhibit excellent catalytic activity in the oxygen evolution reaction for water splitting. In this study, a coating of oxide-carbide composites containing Cr, Fe, Co, Ni, and Mo was electrodeposited in a C₂H₆SO (DMSO)-based solution. X-ray photoelectron spectroscopy (XPS) analysis confirmed the presence of carbides, oxides, and oxygen vacancies. Except for some metallic nickel, most metals exist in the oxidized or hydroxide states. Aqua- and chloro-complexes of metal ions have been proposed to form oxides and carbides on copper via the reduction of hydrated water and organic molecules. The coating exhibited high catalytic activity for the oxygen evolution reaction in an alkaline solution, achieving an overpotential of 216&#xa0;mV, corresponding to a current density of 10&#xa0;mA&#xa0;cm. The long-term stability at the current density of 10&#xa0;mA&#xa0;cm⁻² was investigated for 50&#xa0;h, with a stable overpotential and minor surface dissolution. The catalytic activity was determined using density functional theory, and the unsaturated oxidation number of the metal atoms was calculated to depict the relationship between the binding state and the overpotential of the active sites.</p> Graphical abstract <p></p>