Flexibility Tuning of Dual-Metal S-Fe-Co-N-5 Catalysts with O-Axial Ligand Structure for Electrocatalytic Water Splitting

The electrocatalytic performance of metal-nitrogen-carbon (M -N -C) single-atom catalysts remains a significant challenge due to their rigid active center. Controllable tuning of the local microenvironment and electronic structure is critical for M -N -C single-metal site catalysts in improving the electrochemical performance and exploring the reaction mechanism. Herein, Co -N-4 is selected as a benchmark among various M -N -C catalysts based on theoretical prediction and experimental studies. A dual-metal S -Fe -Co -N-5 catalyst is constructed by embedding Fe and S into the structure of Co -N-4 motifs. Theoretical analysis and in situ characterizations illustrate that the active sites will in situ combine an O-axial ligand to form S -Fe -Co -N-5 -O structure during the oxygen evolution reaction (OER), which can reduce the reaction energy of O*?OOH*. The Ab Initio Molecular Dynamics simulations and deformation energy for H*/O* adsorption reveal that the Fe -Co and S -Fe bonds exhibit flexible characteristics compared to the Co/Fe-N bonds. This flexibility of S -Fe -Co -N-5 -O structure facilitates the OER performance by reducing the OOH*?O-2 , which is the OER rate-determining step, resulting in superior performance. The optimized S -Fe -Co -N-5 -O catalyst exhibits excellent OER (260 mV(1)50 mA cm(-2)) and hydrogen evolution reaction (138 mV(1)10 mA cm(-2)) performance in alkaline electrolytes. The reported regulation strategy ameliorates the micro-environment of Co -N-4 with tunable flexibility, which helps allow a basic comprehension of the electrochemical reaction mechanism.