Hetero-nanojunction armored with carbon layer for boosting water oxidation over RuO₂ in acid

In this work, a high-performance electrocatalyst, (Co₃O₄|RuO₂)@C, was developed for the oxygen evolution reaction (OER) in acid. Despite the low loading of Ru (0.66 wt%) and Co (0.35 wt%), the catalyst exhibited remarkable performance, achieving an overpotential of 202 mV at 10 mA cm⁻². Notably, when employed as an anodic catalyst in a proton exchange membrane (PEM) electrolyzer, (Co₃O₄|RuO₂)@C demonstrated exceptional stability, operating continuously for 300, 100, and 100 h at current densities of 10, 50, and 100 mA cm⁻², respectively. Experiments and theoretical investigations revealed that the regulated electronic structure of RuO₂ by the Co₃O₄|RuO₂ nanojunction, coupled with the carbon coating layer, led to excellent OER performance of (Co₃O₄|RuO₂)@C. The construction of the Co₃O₄|RuO₂ nanojunction triggered the electron transfer from Co₃O₄ to RuO₂, decreasing the energy barrier of *O → *OOH and mitigating the over-oxidation of Ru sites. Furthermore, the carbon layer surrounding the crystalline Co₃O₄|RuO₂ facilitated mass/charge transfer across the electrolyte-catalyst interface and acted as a protective “chain mail” to enhance the durability of (Co₃O₄|RuO₂)@C.