Spin Regulation of Fe Single Site Induced by Adjacent Mg Site Achieving Excellent Oxygen Reduction Catalysis

Metal-nitrogen-carbon catalysts have emerged as promising alternatives to costly platinum group catalysts in fuel cells and metal-air batteries; however, further enhancement of their activity in both alkaline and acidic media is still required. Here, we present a FeMg-N-C dual-atom catalyst that demonstrates excellent oxygen reduction reaction (ORR) performance, achieving notably high half-wave potentials (E_1/2) of 1.004 V in alkaline media and 0.881 V in acidic media. Additionally, the FeMg-N-C catalyst delivers peak power densities of 530.1 mW cm^-2 in Zn-air cells and 1.06 W cm^-2 in H₂-O₂ fuel cells. Experimental and theoretical analyses reveal that the enhanced ORR activity arises from the spin state transition of Fe sites from low spin to medium spin, induced by adjacent Mg sites. This medium-spin Fe site exhibits strong adsorption of *O₂ and weak adsorption of *OH, effectively facilitating the initial ORR step and the removal of *OH. This work paves a novel pathway to design and construct well-performing electrocatalysts via the spin regulation strategy.