Ru–Co alloy coatings electrodeposited on a MAX phase substrate as efficient catalysts for the hydrogen evolution reaction

This study investigates the structure, electrochemical behavior and hydrogen evolution reaction (HER) performance of electrodeposited Ru–Co alloy coatings. The alloys were prepared from a 0.75 M Co2+ + 0.025 M Ru3+ solution at various potentials ranging from −0.5 to −1.2 V vs. SCE. Results reveal that the Ru and Co deposition processes are interdependent. The deposition of nobler Ru from the mixed metal solution reaches pure diffusion control already at −0.7 V compared to −1.0 V from a single Ru bath. On the other hand, Co deposition is significantly facilitated in the presence of Ru in the solution. Consequently, as the deposition potential changes from −0.6 to −1.0 V, Ru–Co solid solution coatings characterized by a distinct globular morphology are formed, with their Co content increasing from 22.1/7.4 to 70.2/86.1 wt% for the Cu/Ti2AlC MAX phase substrate applied. The alloy catalysts are found to show much better HER activity and stability in alkaline than in acidic solutions. The best Ru–Co@Ti2AlC sample, electrodeposited at −0.6 V, requires an overpotential of only −95 mV to deliver a current density of −100 mA cm−2 in 1 M KOH, thus outperforming most Ru–Co-based HER electrocatalysts reported to date.