Flexibility Tuning of Dual-Metal S─Fe─Co─N5 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─N4 is selected as a benchmark among various M─N─C catalysts based on theoretical prediction and experimental studies. A dual-metal S─Fe─Co─N5 catalyst is constructed by embedding Fe and S into the structure of Co─N4 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─N5─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─N5─O structure facilitates the OER performance by reducing the OOH*→O2, which is the OER rate-determining step, resulting in superior performance. The optimized S─Fe─Co─N5─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─N4 with tunable flexibility, which helps allow a basic comprehension of the electrochemical reaction mechanism.