Interfacial Oxygen Spillover From RuO ₂ to MoO ₃ Boosts Electrocatalytic Activity and Stability for Overall Water Splitting in Both Alkaline and Aci

Achieving both high catalytic activity and durable long‐term stability remains a key challenge for efficient water splitting across a wide pH range. Although RuO ₂ is decidedly active for the oxygen evolution reaction (OER), its stability is compromised by over‐oxidation and dissolution under harsh conditions. In this study, we engineered carbon nitride (CN _x ) doped ruthenium molybdenum mixed oxide (RuO ₂ –MoO ₃ /CN _x ) which exhibits excellent bifunctional electrocatalytic performance toward both HER and OER in acidic and alkaline media. In 1 M KOH, it delivers low overpotentials of 19 mV for HER and 250 mV for OER at a current density of 10 mA/cm ² . Notably, the catalyst also maintains appreciable activity under acidic conditions. The superior performance of RuO ₂ –MoO ₃ /CN _x originates from oxygen spillover at the RuO ₂ –MoO ₃ interface, where reactive oxygen species migrate to MoO ₃ , suppressing over‐oxidation of Ru active sites and enhancing durability. Concurrently, strong interfacial electronic interactions optimize adsorption of reaction intermediates and accelerate kinetics. Together with high surface area, efficient mass and electron transport, these features enable excellent catalytic activity across both acidic and alkaline media, providing an effective strategy for the design of robust electrocatalysts for green and renewable energy conversion.