Magnetic Field‐Driven Spin State Transformation in Promoting the Catalytic Activity of Doped Single‐Atom for 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 Ru SAs /Ni 2 P@Fe 3 O 4 core‐shell catalyst is designed, which synergizes Ru single‐atoms (SAs) doping and external magnetic field excitation. Under a 0.3 T magnetic field, Ru SAs /Ni 2 P@Fe 3 O 4 −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 Fe 3+ (from low‐spin to high‐spin), enhancing interfacial charge transfer and enriching electron density around Ru SAs. These effects optimize hydrogen adsorption free energy (ΔG H* ) and reaction kinetics. The Ru SAs serve as the dominant active sites, while the spin‐state reconfiguration of the Fe 3 O 4 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.