Cobalt spin state engineering via secondary coordination environment modulation for enhanced oxygen evolution...

The oxygen evolution reaction (OER), a critical process for energy production and conversion, is often hindered by unappropriated energy barriers. The spin state, as one of the most fundamental characteristics of electron, is directly correlated with electron transfer and the process of bonding orbital hybridization. Precisely tailoring spin-state engineering with intermediate spin (IS) state for better adsorption for oxygen intermediates (O*) and enhance OER is important but challenging. Herein, we present the unique CoMoOOH/Co₃S₄ catalyst originating from the in-situ reconstruction of pre-catalysts via secondary coordination environment (SCE) modulation. Density functional theory (DFT) calculations is systematically employed to assess the charge transfer capacity and adsorption energy to guide heteroatoms modification. Comprehensive analysis discovers that Mo modification in SCE induces a distortion in CoO₆ units and reduces the crystal field splitting energy, prompting partial t_2g electron transition into the e_g orbitals thereby generating and stabilizing the IS Co³⁺ species. These unpaired e_g electrons subsequently facilitate electron transition and hybridization between O* and Co active sites, thereby effectively reducing the energy barriers and enhancing the OER activity (a low η₁₀ of 186 mV). This work provides thoughtful insights into the electronic structure-function relationship which is significant for the advancement of various sustainable energy conversions.