Synergy of controlled cobalt incorporation and oxygen vacancies in Mn-based spinel electrocatalysts for durable and efficient lattice oxygen evolution

In the context of OER mechanisms, the lattice oxygen-mediated mechanism has garnered research interest due to its potential to break the scaling limitation of the adsorbate evolution mechanism. Although various strategies for enhancing the activity of spinel-based catalysts have been reported, the factors influencing catalyst stability via the LOM pathway have not been investigated extensively. The AB₂O₄ crystal structure of spinel oxides offers structural and compositional flexibility, enabling comprehensive mechanism exploration. To this end, an efficient and straightforward synthesis method is necessary to precisely control geometric configuration and cation incorporation in spinel. Herein, a one-step CV deposition method is proposed to fabricate freestanding Mn-based spinel catalysts with abundant surface oxygen defects and a nanosheet-like morphology under mild conditions. This method allows precise regulation of Co incorporation and adjustment of geometric configuration by modifying the electrolyte composition and concentration. Given that cobalt ions possess more outer electrons and lower field stabilization compared to Mn³⁺ in an octahedral field, appropriate Co doping accelerates the refilling process of oxygen vacancies and stabilizes Mn-based spinel framework. Systematic experiments and density functional theory studies suggest that appropriate Co doping significantly enhances both activity and stability of spinel oxides, with precise control of incorporation content being crucial. Consequently, the fabricated Co-incorporated ZnMn₂O₄ with a Co/Mn ratio of ∼0.2 exhibits superior activity and stability toward the OER. The assembled ZAB demonstrates excellent cycling endurance. This synthesis strategy can be extended to other spinel structures, potentially providing insights for further mechanism exploration of spinel in broader fields.