Three-dimensional porous metal phosphide cathode electrodes prepared via electroless galvanic modification for alkaline water electrolysis

Abstract

Green hydrogen production from water electrolysis is crucial to propelling power-to-X strategies, and a central role in this strategy depends on innovative catalysts used in different electrolyzer technologies. The present study combines galvanic replacement and low-temperature annealing to construct a self-supported and low Ru-loaded metal phosphide electrode for efficient alkaline hydrogen evolution reaction (HER). The non-platinum electrode (catalyst + porous transport layers) fabricated over three-dimensional nickel foam (Ni₂P–Ru/NF) yielded an overpotential of 40 mV for 10 mA cm⁻² in 1 M KOH during the HER and also demonstrated excellent durability under varying conditions for 48 h. A comprehensive analysis of surface characteristics followed by first principles calculations specified the factors, surface modification and active sites favoring excellent HER performance for Ni₂P–Ru/NF. The most favorable hydrogen adsorption (ΔG_H*) value, from DFT calculations, was identified for the Ru site in Ni₂P–Ru, which was also very similar to the Pt/C system. Finally, the overall water splitting study performed using the Ni₂P–Ru/NF catalyst as the cathode (Ni₂P–Ru/NF‖IrO₂) showed the compatibility of the self-supported catalyst for efficient electrolysis with a noteworthy performance of 1.6 V for 10 mA cm⁻². The study showcases a potential pathway for applying very low Ru-loaded, self-supporting and carbon-free metal phosphide electrodes in commercial water electrolyzer systems for efficient green hydrogen generation.