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 Co_SA+NC/NPSC. In the Co_SA+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 Co_SA+NC/NPSC demonstrates an impressive oxygen evolution reaction activity (E_j=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 Co_SA+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.