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

## TL;DR

A new dual-atom catalyst with Fe and Mg improves oxygen reduction reactions in energy devices by regulating the spin state of Fe atoms.

## Contribution

The use of adjacent Mg sites to induce a spin state transition in Fe atoms for enhanced ORR performance is novel.

## Key findings

- The FeMg–N–C catalyst achieves high half-wave potentials of 1.004 V in alkaline and 0.881 V in acidic media.
- The catalyst delivers peak power densities of 530.1 mW cm−2 in Zn–air batteries and 1.06 W cm−2 in H2–O2 fuel cells.
- Spin regulation via Mg sites optimizes *O2 adsorption and *OH desorption, enhancing the 4-electron ORR pathway.

## Abstract

The FeMg–N–C dual-atom catalyst demonstrates excellent oxygen reduction reaction (ORR) performance, achieving notably high half-wave potentials of 1.004 V in alkaline and 0.881 V in acidic media.Adjacent Mg sites induce the spin state transition of Fe from low spin to medium spin, optimizing the adsorption of *O2 and desorption of *OH, thereby accelerating the 4-electron ORR pathway.The catalyst enables outstanding practical performance in energy devices, delivering peak power densities of 530.1 mW cm−2 in Zn–air batteries and 1.06 W cm−2 in H2–O2 fuel cells.

The FeMg–N–C dual-atom catalyst demonstrates excellent oxygen reduction reaction (ORR) performance, achieving notably high half-wave potentials of 1.004 V in alkaline and 0.881 V in acidic media.

Adjacent Mg sites induce the spin state transition of Fe from low spin to medium spin, optimizing the adsorption of *O2 and desorption of *OH, thereby accelerating the 4-electron ORR pathway.

The catalyst enables outstanding practical performance in energy devices, delivering peak power densities of 530.1 mW cm−2 in Zn–air batteries and 1.06 W cm−2 in H2–O2 fuel cells.

The online version contains supplementary material available at 10.1007/s40820-026-02143-6.

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 (E1/2) 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.

The online version contains supplementary material available at 10.1007/s40820-026-02143-6.