# Magnetic Field‐Driven Spin State Transformation in Promoting the Catalytic Activity of Doped Single‐Atom for Hydrogen Evolution Reaction

## TL;DR

A new catalyst uses magnetic fields and single-atom doping to boost hydrogen production efficiency by altering electron behavior.

## Contribution

Introduces a dual-regulation mechanism combining atomic doping and magnetic spin-state transformation for enhanced catalytic performance.

## Key findings

- The catalyst achieves a low overpotential of 38.9 mV at 10 mA cm−2 under a 0.3 T magnetic field.
- Magnetic fields induce a spin-state transition in Fe3+, improving electron transfer and hydrogen adsorption.
- Ru single-atoms are identified as the dominant active sites for the hydrogen evolution reaction.

## Abstract

Developing efficient electrocatalysts for the hydrogen evolution reaction (HER) requires innovative strategies to modulate electronic structures and reaction kinetics. Herein, a ferromagnetic RuSAs/Ni2P@Fe3O4 core‐shell catalyst is designed, which synergizes Ru single‐atoms (SAs) doping and external magnetic field excitation. Under a 0.3 T magnetic field, RuSAs/Ni2P@Fe3O4−0.3 T achieves a remarkably low overpotential of 38.9 mV at 10 mA cm−2 and a Tafel slope of 39.5 mV dec−1 in alkaline media, outperforming its counterparts without magnetic stimulation. Advanced characterization (XANES, Mössbauer, EPR, SQUID) and density functional theory calculations reveal that the magnetic field induces a spin‐state transition in Fe3+ (from low‐spin to high‐spin), enhancing interfacial charge transfer and enriching electron density around Ru SAs. These effects optimize hydrogen adsorption free energy (ΔGH*) and reaction kinetics. The Ru SAs serve as the dominant active sites, while the spin‐state reconfiguration of the Fe3O4 core under magnetic fields stabilizes the structure and accelerates electron transfer. This work unveils a dual‐regulation mechanism combining atomic doping and spin engineering, offering a novel pathway for designing high‐performance catalysts via electronic and magnetic synergy.

A ferromagnetic RuSAs/Ni2P@Fe3O4 material is designed via a synergistic strategy of single‐atom doping and magnetic field‐driven spin‐state transformation. This strategy introduces new Ru single‐atom active sites for the hydrogen evolution reaction and facilitates the transition of Fe3+ (3d t2g) low‐spin electrons to a high‐spin state (3d eg). Consequently, electron transfer to the Ru single‐atom is enhanced, boosting overall catalytic efficiency.