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 Co 2+ 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 ( T N = 25 K) to ferromagnetic coupling ( T C > 850 K). This Co Oh -d orbital engineering enhances carrier concentration and decreases electron transfer resistance. Electrochemical analysis reveals that the Co 3 O 3.65 B 0.35 exhibits exceptional catalytic performance, achieving an overpotential of 295 mV at 30 mA cm –2 compared to 441 mV for pristine Co 3 O 4 . 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.