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

Spin engineering via Mn doping precisely steers Co spin state in NiCo 2 O 4 , beyond the conventional d-band center regulation. • Mn-NCO exhibits a low overpotential of 265 mV at 10 mA cm -2  and outstanding durability over 500 h in alkaline electrolyte. • Mn acts as a spin switch to optimize *O adsorption, lowering rate‑limiting barrier from 2.84 to 1.64 eV. • Practical potential is demonstrated via a stable AEM water electrolyzer, bridging fundamental research and application. 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 NiCo 2 O 4 (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. Mn doping serves as a spin switch in NiCo 2 O 4 electrocatalyst, modulating the active Co site from high spin to low spin state to optimize *O adsorption and significantly lower the rate-determining step energy barrier from 2.84 to 1.64 eV. Download: Download high-res image (244KB) Download: Download full-size image