Ferromagnetic Surface Segregation via Stress-Concentration Coupling Boosts the Oxygen Evolution Reaction in RuO₂

RuO2, the benchmark catalyst for the oxygen evolution reaction (OER), has traditionally been considered Pauli paramagnetic; however, recent findings have demonstrated its antiferromagnetic (AFM) properties, hinting at the opportunity to enhance RuO2's OER performance by manipulating its magnetic traits. In this study, we successfully induced weak ferromagnetism in commercial RuO2, transitioning it from an AFM state using an electrochemical sodiation method. This process resulted in high activity, achieving an overpotential of 145 mV to reach 10 mA cm–2 and extending the service hours by more than 13 times compared to pristine RuO2 in 0.5 M H2SO4. A combination of experimental and theoretical analyses indicated that the sodiation triggers significant surface compressive stress, leading to lattice distortion and disruption of the pristine structural symmetry of RuO2. Consequently, orbital degeneration ensues, prompting individual spin-up d electrons to jump to the high-spin state. This mechanism drives the conversion from AFM to weak FM behavior for RuO2, ultimately yielding exceptional catalytic activity and stability.