A Phosphorus‐Bridged Spin Trigger for Oxygen Reduction

Abstract Precise control over the spin degree of freedom of catalytic metal centers represents a significant challenge in enhancing the oxygen reduction reaction (ORR). In this work, we report a phosphorus(P)‐bridged composite comprising Fe single atoms (SAs) and atomic clusters (ACs), Fe SA/AC /PNC, wherein the Fe SA ‐P‐Fe AC structure functions as an efficient electron channel and, more importantly, a spin trigger. This trigger induces a spin‐state transition of Fe II from low‐spin (S = 0) to medium‐spin (S = 1), as unequivocally deciphered by advanced spectroscopic and magnetic analyses. This spin‐state reconstruction directly optimizes the reaction pathway by enhancing O 2 adsorption and facilitating *OH desorption. The resulting catalyst exhibits exceptional oxygen reduction activity in both acidic and neutral media, with half‐wave potentials of 0.852 and 0.831 V, respectively, and achieves a peak power density of 1.35 W cm −2 in proton exchange membrane fuel cells (PEMFCs). This strategy is universally effective for Co and Ni systems, establishing spin‐state engineering as a general principle for designing high‐performance non‐precious metal catalysts.