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.