Surface Adsorption of Amorphous Phosphate on RuNi-Doped Molybdate for the Hydrogen Evolution Reaction

Developing highly active and cost-effective electrocatalysts is critical for enhancing the intrinsic performance of electrocatalytic water splitting. Oxoanion-based compounds, such as phosphates and molybdates, have emerged as promising electrocatalysts owing to their advantageous properties of nontoxicity, low price, and strong water adsorption ability. However, their relatively inferior activity has impeded extensive investigation into electrochemical applications. Herein, an amorphous phosphate-adsorbed and RuNi-doped molybdate (RuNiMo-P) composite is synthesized on nickel foam (NF) support by using a simple two-step method. Significantly, an acidic solution of phosphomolybdic acid (PMo₁₂), containing a low concentration of Ru, can etch the NF, contributing to the in situ growth of the RuNi-doped molybdate precursor. Subsequent phosphating ensures the surface formation of the amorphous phosphate layer due to abundant oxygen in the precursor. The strong structural interaction between RuNi-doped molybdate and amorphous phosphate in RuNiMo-P prompts an enhanced hydrogen evolution reaction (HER) performance, delivering an overpotential of 38 mV at a current density of -10 mA cm^-2, a Tafel slope of 53 mV dec^-1, and good stability in an alkaline medium. Characterizations after HER reveal that RuNi doping, partial dissolution of phosphate and molybdate species, and newly formed NiOOH nanosheets can expose active sites, facilitate charge transfer, and modify electronic structures, thereby improving the HER performance effectively.