Electronic Backflow Through Oxygen Bridge in RuO _x ‐Graphdiyne for Stable Acidic Water Oxidation

Abstract Developing cost‐effective and stable catalysts for oxygen evolution reaction (OER) in proton exchange membrane water electrolyzers (PEMWE) remains a significant challenge. Although RuO ₂ shows promise as an alternative to the expensive IrO _x , its large‐scale application is hindered by the over‐oxidation of Ru into soluble high‐valent species (> +4). In this work, the in situ growth of RuO _x species on graphdiyne (GDY) is reported, establishing strong electronic metal‐support interaction to form the Ru─O─C oxygen bridge structure. Interestingly, in situ X‐ray absorption spectroscopy (XAS) at Ru K ‐edge reveals an unexpected electronic backflow on the Ru sites under positive potential during OER, leading to a stable low chemical state of Ru. As another aspect, in situ XAS at C K ‐edge shows the process of GDY losing electrons during OER, confirming the electron injection from C to Ru through the oxygen bridge structure. This electronic backflow process can block the over‐oxidation of Ru. As a result, the RuO _x ‐GDY catalyst exhibits a low overpotential of 193 mV at 10 mA cm ⁻² with remarkable stability over 300 h (a degradation rate of only 0.13 mV h ⁻¹ ). In the PEMWE, the catalyst achieves a cell voltage of 1.72 V at 1 A cm ⁻² , outperforming the conventional RuO ₂ (1.91 V).