Spin engineering of NiCo₂O₄ via Mn doping for steering the oxygen evolution reaction pathway

While regulating the d-band center is a widely adopted strategy for optimizing oxygen evolution reaction (OER) electrocatalysts, it often lacks the precision required for selectively lowering the high energy barrier of the rate-determining step (e.g., *O → *OOH). This work introduces a spin engineering approach via manganese (Mn) doping to effectively tailor the electronic structure of NiCo₂O₄ (NCO). The Mn-doped NCO porous microspheres, synthesized through a facile solvothermal-oxidation route, deliver outstanding OER performance in 1.0 M KOH, requiring an overpotential of only 265 mV to achieve 10 mA cm^-2 current density and maintaining exceptional stability for 500 h. Moreover, the catalyst shows great promise in an anion exchange membrane water electrolyzer. Density functional theory calculations disclose that Mn serves as a "spin switch", promoting a transition of Co active sites from high-spin (magnetic moment ∼2.4 μB) to low-spin (∼1.9 μB) states. This spin-state modulation selectively weakens the adsorption of the critical *O intermediate, thereby markedly reducing the energy barrier of the rate-determining step from 2.84 eV to 1.64 eV, without significantly perturbing other intermediates. This work not only reports a highly active OER electrocatalyst but also illuminates the pivotal role of spin-state manipulation, offering a new paradigm for designing high-performance electrocatalytic materials.