γ-NiFe core-shell catalysts by synergistic tuning of spin state and d-band for boosted oxygen evolution

Oxygen evolution reaction (OER) remains a key challenge for hydrogen production by water electrolysis. NiFe-based electrocatalysts rank among the most active in alkaline media, but surface-centric models emphasizing reconstructed oxyhydroxides have not clarified Fe's contribution, hindering addressing OER's inherent scaling and spin-related limitations. Herein, we show engineering the bulk spin-electronic structure of a Ni-Fe alloy regulates surface catalysis. A strongly coupled core–shell catalyst is made by integrating a magnetic γ-Ni_0.86Fe_0.14 alloy core with a thin amorphous NiFe (oxy)hydroxide shell via hydrogen bubble-templated electrodeposition and controlled alkaline corrosion. With a disordered ferromagnetic ground state and converged Ni/Fe d-band centers, it creates complementary majority-spin Fe and minority-spin Ni charge transfer channels. This spin-polarized d-band effect localizes charge at Ni-Fe bridge sites, enhances *OOH binding, and lowers the barrier for *O → *OOH in adsorbate-evolution mechanism (AEM). Consequently, the catalyst achieves 10 mA cm⁻² at 176 mV and 37 mV dec⁻¹ Tafel slope, sustaining 500 mA cm⁻² for over 10 days with negligible degradation with Fe³⁺/Ni²⁺ replenishment. Its activity matches the theoretically calculated overpotential. Our findings show the bulk alloy phase shifts from a passive scaffold to an active OER regulator via spin polarization-d-band engineering coupling, providing new insights for high-performance catalyst design.