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

Abstract

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@50 mA cm ⁻²) and hydrogen evolution reaction (138 mV@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.