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+Oh, 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 (TN = 25 K) to ferromagnetic coupling (TC > 850 K). This CoOh-d orbital engineering enhances carrier concentration and decreases electron transfer resistance. Electrochemical analysis reveals that the Co3O3.65B0.35 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%. In-situ 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.