# Modulation of the Spin State of Atomic Fe-N4 Sites with Interlayer-Adjacent Ir-N4 for Superior ORR Activity

## TL;DR

This paper introduces a new bimetallic catalyst that improves oxygen reduction reaction efficiency and battery performance by modulating the spin state of iron atoms.

## Contribution

The novel use of interlayer-adjacent Ir-N4 to modulate the spin state of Fe-N4 sites, enhancing ORR activity and battery performance.

## Key findings

- Ir-N4 induces a low-spin to medium-spin transition in Fe centers, improving ORR activity with a half-wave potential of 0.928 V.
- The 3D macroporous carbon framework enables high discharge power density (314 mW cm⁻2) and cycling stability in Zn-air batteries.
- Theoretical and experimental analysis confirms enhanced electron delocalization and oxygen intermediate adsorption energies.

## Abstract

Ir-N4 induce spin polarization and trigger a low-spin to medium-spin transition at Fe centers, enhancing electron delocalization in Fe-O frontier orbitals, optimizes oxygen intermediate adsorption energies.Modulation of spin state of active center optimizes the adsorption energy and enhancing intrinsic catalytic activity (E1/2 = 0.928 V for oxygen reduction reaction).3D ordered macroporous carbon framework ensures high accessibility of atomic sites, resulting in excellent batteries performance, i.e., a discharge power density of 314 mW cm−2, specific capacity of 817.5 mAh g−1.

Ir-N4 induce spin polarization and trigger a low-spin to medium-spin transition at Fe centers, enhancing electron delocalization in Fe-O frontier orbitals, optimizes oxygen intermediate adsorption energies.

Modulation of spin state of active center optimizes the adsorption energy and enhancing intrinsic catalytic activity (E1/2 = 0.928 V for oxygen reduction reaction).

3D ordered macroporous carbon framework ensures high accessibility of atomic sites, resulting in excellent batteries performance, i.e., a discharge power density of 314 mW cm−2, specific capacity of 817.5 mAh g−1.

The online version contains supplementary material available at 10.1007/s40820-026-02108-9.

Development of efficient and durable oxygen reduction reaction (ORR) electrocatalysts is of great interest yet remains challenging. Herein, we predicted and screened a bilayer graphite carbon-supported Ir-N4/Fe-N4 catalyst with high ORR activity using density functional theory calculations. Subsequently, various bimetallic single atom supported on 3D ordered macroporous carbon were rationally designed and experimentally synthesized via a colloidal microsphere template-confined reaction method. As anticipated, the resulting Ir-N4/Fe-N4 bimetallic single-atom catalysts (IrFe-SACs) exhibit superior ORR activity and durability, reaching a half-wave potential of 0.928 V. The IrFe-SACs also demonstrate outstanding performance in Zn-air batteries, including a high discharge power density (314 mW cm⁻2) and excellent cycling stability (~ 1650 cycles over 550 h). Further experimental characterizations and theoretical analysis reveal that introducing interlayer-adjacent Ir-N4 sites facilitates the transition of Fe-N4 from a low-spin state to a medium-spin state, which optimizes the spin polarization of Fe 3d orbitals and enhances the non-localization of the Fe–O/OH molecular orbital, thereby significantly improving the ORR intrinsic activity and durability of atomic Fe-N4 sites.

The online version contains supplementary material available at 10.1007/s40820-026-02108-9.