Uncoordinated Single‐Site Ru Confined in Spinel Co ₃ O ₄ Lattice for High‐Performance and Low‐Cost PEM Water Electrolysis

Abstract Ruthenium‐based catalysts have emerged as cost‐effective and active alternatives to iridium‐based materials for acidic oxygen evolution reaction (OER) in proton exchange membrane (PEM) water electrolysis. However, their widespread application is constrained by poor stability under high current densities. Herein, an uncoordinated single‐site Ru catalyst embedded within spinel Co ₃ O ₄ lattice is developed, delivering a current density of 3.0 A cm ^{− 2} at 2.02 V with an ultra‐low loading of 13.8 µg _Ru cm ^{− 2} and excellent durability over 300 h at 0.7 A cm ^{− 2} . Notably, a low energy consumption of 46.1 kW h kg ⁻¹ H ₂ with an ultralow noble metal cost of 2.1 $ m ^{− 2} is achieved, far exceeding commercial RuO ₂ (48.6 kW h kg ^{− 1} H ₂ and 2280 $ m ^{− 2} ) and most reported Ir‐based catalysts. In situ spectroscopy and theoretical simulations reveal strong electronic metal–support interactions (EMSI) between Ru single site and Co ₃ O ₄ effectively modulate the Ru electronic structure and simultaneously activate adjacent Co sites, lowering the OER energy barrier for activity enhancement. Additionally, the EMSI imparts the catalyst with redox reversibility and structural flexibility, mitigating subsurface oxygen loss and suppressing over‐oxidation and dissolution of both Ru and Co for sustaining stability. This work provides a promising design strategy for advanced Ru‐based catalysts as promising alternatives to IrO ₂ for PEM water electrolysis.