Synergistic Modulation of Ru–O Bond Covalency via Ba/Fe Co‐Doping and Oxygen‐Vacancy Engineering for Efficient Wide‐pH Oxygen Evolution

Developing efficient and stable oxygen evolution reaction (OER) catalysts across a wide-pH range is critical for practical water electrolysis. Here, it is demonstrated that co-doping Ba and Fe into RuO₂, together with oxygen vacancy engineering, synergistically tailors the Ru-O bond covalency, yielding highly active and durable OER catalysis across acidic, alkaline, and neutral media. Structural and spectroscopic analyses (XRD, XPS, and XAS) reveal that Ba doping expands the Ru-O bond length and weakens electron cloud overlap, whereas Fe doping contracts the bond and strengthens covalency. Their cooperative effect in co-doped RuO₂ produces a moderate Ru-O bond covalency, balancing adsorption energies of OER intermediates. Density functional theory further confirms that the neighboring Ru sites near dopants and oxygen vacancies provide optimal adsorption, lowering the rate-limiting barrier. This covalency tuning strategy endows co-doped RuO₂ with both high intrinsic activity and structural stability, as evidenced by low overpotentials of 174, 236, and 284 mV at 10 mA cm² in acidic, alkaline, and neutral electrolytes, and over 360 h of continuous operation with negligible degradation. This work highlights Ru-O bond covalency modulation as an effective design principle for wide-pH, high-performance Ru-based OER catalysts.