Electrodeposition of Mo-Rich NiMo Catalysts: Effect of Deposition Parameters and Oxygen Content on the Alkaline Hydrogen Evolution Reaction Activity

Electrodeposited Mo-rich NiMo catalysts offer enhanced catalytic activity for the alkaline hydrogen evolution reaction (HER) and provide an electrically conductive, binder-free substrate connection, making them promising catalysts for green hydrogen production. However, creating Mo-rich deposits is challenging, as the codeposition process typically favors Ni. Optimal deposition conditions for Mo-rich NiMo catalysts remain insufficiently explored. This article investigates Mo-rich NiMo electrodeposition from an ammonia-free citrate bath using NaSO4 as a chlorine-free support electrolyte. The effects of the deposition parameters, 1) sodium molybdate concentration in the electrolyte, 2) deposition current density, and 3) enhanced mass transport via working electrode rotation on the alkaline HER activity, were studied. The electrodeposits, containing 44-66 wt% Mo, exhibited increased surface area due to a rough, cracked morphology and variable oxygen content of the catalyst. The oxygen content was linked to HER activity, revealing an inhibiting effect. The lowest overpotential of 118 mV at -10  mA cm-2 for the alkaline HER was achieved using an electrolyte with 0.02 mol L-1 sodium molybdate, a deposition current density of 600 mA cm-2, without electrode rotation. Respective samples combined a favorable Ni:Mo ratio comprising 56 wt% Mo content with increased surface area and low oxygen content.