Effect of copper addition on cobalt-molybdenum electrodeposited coatings for the hydrogen evolution reaction in alkaline medium

Co–Mo materials have been reported as electrocatalysts that present good performance in alkaline electrolytes. In this paper, the addition of copper into Co–Mo catalysts was evaluated for the hydrogen evolution reaction (HER). It was observed that the electrochemical activity of the Co–Mo for the HER benefited from the addition of copper. The overpotentials required to reach a current density of −10 mA cm−2 were of −156 mV and −119 mV for Co67Mo33 and Co56Mo21Cu23, respectively. Besides the increased surface area resulting from the addition of copper, it was observed that the improved intrinsic activity for Co61Mo32Cu7, compared to Co67Mo33, is related to a thermodynamic favoring of the hydrogen adsorption and desorption stages. Large quantities of copper do not favor the HER; therefore, the increased catalytic activity depends on a balance between the intrinsic catalytic activity and the increase of the electroactive area.