Modulating electronic structure of Co-N5S1 sites in Co single atom catalysts via phosphorus incorporation and nanoclusters to promote oxygen electrocatalytic activity

Atomically dispersed metal catalysts coordinated with nitrogen coordination and anchored to carbon substrates (M-N-C) have become highly effective alternatives to platinum-group catalysts for oxygen electrocatalysis. However, the catalytic efficacy of M-N-C systems remains constrained by the suboptimal performance associated with the symmetric charge distribution around the active metal centers. The synergistic co-design of asymmetric metal single-atom catalytic centers with heteroatom doping significantly enhances the bifunctional oxygen electrocatalytic activity and durability, advancing the capabilities of next-generation flexible zinc-air batteries. Herein, we developed a pyrolysis-secondary coordination strategy to generate a bifunctional oxygen electrocatalyst, characterized by single Co atoms integrated within an asymmetrical Co-N5S1 moiety, along with nanocluster complexes embedded in N,P,S-codoped carbon frameworks, labeled CoSA+NC/NPSC. In the CoSA+NC/NPSC catalyst, the Co-N5S1 active sites exhibit an optimized electronic configuration, achieved through the synergistic coordination of heteroatom doping and nanocluster integration. Theoretically, this configuration significantly lowers the energy barriers and adjusts the d-band center, ensuring a more balanced binding strength between active sites and the oxygen-containing intermediates and contributing to the promoted bifunctional oxygen reduction reaction/oxygen evolution reaction efficiency. The experimentally analytical results reveal that the CoSA+NC/NPSC demonstrates an impressive oxygen evolution reaction activity (Ej=10 = 1.58 V) and a narrow bifunctional potential gap (ΔE = 0.75 V), remarkably superior to the counterparts with symmetric Co-S coordination or phosphorus-free doping. When assembled as an air electrode, the CoSA+NC/NPSC-based flexible zinc-air battery exhibits ultralong charge-discharge life (> 105 h) and impressive initial round-trip efficiency of 72.42% even at 0 °C.