Tailoring the Chemical Environment of Ru–Mo Composites for Efficient Hydrogen and Oxygen Evolution Reactions

The development of cost‐effective and stable electrocatalysts that can replace the prevailing Pt‐based and Ir‐based catalysts for water splitting remains a formidable challenge. The electrocatalytic performance of a catalyst depends on its chemical composition and environment during catalysis. Herein, a Ru–Mo composite is used as an example to highlight the significance of tailoring the chemical environments of the active‐sites. This customization enhances the cathodic and anodic reactions involved in water splitting, ultimately leading to an improved full reaction efficiency. Specifically, the chemically reduced state of Ru–Mo demonstrates promising hydrogen evolution activity and exhibits low overpotentials of 48 and 34 mV at the current density of 10 mA cm−2 in acidic and alkaline electrolytes, respectively. The chemically oxidized state of Ru–Mo, derived from the same precursor, demonstrates proficient oxygen evolution activity and exhibits low overpotentials of 260 and 270 mV at 10 mA cm−2 in acidic and alkaline electrolytes, respectively. Additionally, in both cases, the Ru–Mo composites exhibit significantly improved stability under typical water‐splitting conditions. Despite the close chemical compositions of these two catalysts, they show poor performance in the counter electrode reactions, demonstrating the importance of establishing a suitable chemical environment for efficient electrocatalysis.