Lanthanide–O–Ru on RuO₂ Mediates the Binding Behavior of OH, Enabling Efficient and Stable Water Oxidation in Acidic Solution

The development of Ru-based electrocatalysts with superior activity and stability for proton exchange membrane water oxidation remains a significant challenge. A key strategy is the precise engineering of the lanthanide–O–Ru structure to tailor surface species and continuously modulate Ru–O covalency, thereby optimizing the adsorption energy of intermediate species for enhanced catalytic performance. In this study, density functional theory (DFT) calculations predict that incorporating the late lanthanides (Tm–O–Ru) into the RuO2 structure significantly enhances the density of states near the Fermi level to a greater extent than the middle lanthanide (Gd–O–Ru). This leads to a lower energy barrier for *OOH as the rate-determining step of the oxygen evolution reaction (OER). Additionally, the strength of *OH adsorption follows the Tm–O–Ru > Gd–O–Ru > RuO2 trend. Experimental results confirm the theoretical predictions: Tm–O–Ru structure enhances the Ru–O covalency, tunes the electronic structure of Ru, and optimizes *OH adsorption. These modifications result in good OER performance with an overpotential of 201 mV and robust stability over 1000 h at 10 mA cm–2. Furthermore, a Tm–RuO2-based PEMWE device stably operates at 100 mA cm–2 for 200 h with a low degradation rate of 0.195 mV h–1, outperforming most Ru-based catalysts reported in the literature.