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

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.