Engineering d–d Coupling-Induced Ferromagnetic Catalysts for Boosting the Spin-Polarized Water Oxidation

Spin catalysts have attracted growing research interest, due to their unique spin-selective magneto-electric properties. However, the rational design of high-performance spin catalysts featuring both ferromagnetic ordering and high conductivity remains a formidable challenge in overcoming the efficiency bottleneck of spin-selective water electrolysis. Herein, we raise an anion-mediated d-d coupling strategy by introducing B substitution at the oxygen positions. This modification generates high-spin Co²⁺_<i>Oh</i>, resulting in a substantial enhancement of the density of states near the Fermi level. The orbital conjugation between adjacent Co-O/B-Co units undergoes a dramatic magnetic transition, switching from antiferromagnetic coupling (<i>T</i>_N = 25 K) to ferromagnetic coupling (<i>T</i>_C > 850 K). This Co_<i>Oh</i>-d orbital engineering enhances carrier concentration and decreases electron transfer resistance. Electrochemical analysis reveals that the Co₃O_3.65B_0.35 exhibits exceptional catalytic performance, achieving an overpotential of 295 mV at 30 mA cm^-2 compared to 441 mV for pristine Co₃O₄. Moreover, an applied magnetic field of 500 mT further reduce overpotential by 25.3%. <i>In-situ</i> ATR-SEIRAS, together with theoretical calculations, reveals a substantial enhancement in orbital overlap between Co 3d and O 2p states upon spin alignment, which strengthens σ-bonding interactions and promotes the adsorption of *OOH intermediates. This study offers a viable strategy for the rational design of ferromagnetic OER catalysts through engineering d-d exchange interactions, with broader implications for the development of magnetic field-responsive electrocatalysts.