Interface-induced built-in magnetic field boosted spin exchange interactions to enable high-efficiency oxygen electrocatalysis

Magnetism-promoted electrocatalysis can accelerate spin-constrained reactions and break the limitation of conventional scaling relationships during oxygen electrocatalysis. However, precise spin polarizability ( SP ) regulation under external magnetic fields remains challenging, and the underlying mechanism is elusive. Here, we construct antiferromagnetic/ferromagnetic NiO/NiFe₂O₄ heterostructures to generate a controllable built-in magnetic field (BIMF) for intrinsic SP modulation toward efficient oxygen evolution. Strong interfacial spin interactions trigger a peak BIMF of 2.59 kOe and 60.8% SP for NiO/NiFe₂O₄-0.1, thereby delivering an approximate 1,671% enhancement in current density at 1.7 V (vs. reversible hydrogen electrode [RHE]) compared with NiFe₂O₄. In situ experimental and theoretical results reveal that the enhanced SP optimizes adsorption of oxygen intermediates and accelerates spin-selective electron transfer, and these effects lower the reaction barriers. SP further serves as a descriptor linearly correlated with reaction activity. This work establishes design principles for efficient spin electrocatalysts by using an internal magnetism approach and advances our understanding of spin-driven electrocatalysis mechanisms.