Intrinsic Ferromagnetism Coupling‐Driven the Spin Reconfiguration of Single‐Atom Ru for Enhanced Acidic Water Oxidation

Abstract Oxygen evolution reaction (OER) is essential for electrochemical water splitting and renewable hydrogen production. Ruthenium‐based catalysts exhibit excellent performance but suffer from insufficient stability to practical application. Herein, a spin‐state engineering strategy is explored to modulate the spin‐electron distribution of Ru single atoms via the intrinsic magnetism of Mn ₅ O ₈ substrate for efficient acidic OER. In Ru─Mn ₅ O ₈ system, the favorable Ru ⁴⁺ ‐O‐Mn ²⁺ configuration facilitates Ru‐site spin polarization and drives Ru ⁴⁺ from low‐spin to high‐spin through strong ferromagnetic coupling, whereas Ru ⁴⁺ remains low‐spin in nonferromagnetic Ru─MnO ₂ . Unpaired d _π electrons of high‐spin Ru ⁴⁺ enhance π‐donation to coordinated O ²⁻ , optimizing Ru─O orbital overlap. Moreover, the interaction between high‐spin Ru ⁴⁺ and key intermediates is strengthened. Consequently, Ru─Mn ₅ O ₈ achieves a low overpotential of 186 mV at 10 mA cm ⁻² and sustains stability over 160 h at 100 mA cm ⁻² in acidic medium, outperforming Ru─MnO ₂ (440 mV, 30 h) and commercial RuO ₂ (250 mV, 40 h). When applied as an anode in a proton exchange membrane water electrolyzer, Ru─Mn ₅ O ₈ realizes 1 A cm ⁻² at 1.68 V and maintains stable operation for over 50 h. This work proposes a ferromagnetic interaction‐driven spin modulation strategy, offering a robust pathway for designing high‐performance electrocatalysts for acidic water oxidation.