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

ABSTRACT 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 RuO ₂ , 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 RuO ₂ 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 RuO ₂ with both high intrinsic activity and structural stability, as evidenced by low overpotentials of 174, 236, and 284 mV at 10 mA cm ² 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.