Asymmetric low-coordination tailoring of single-atom cobalt catalysts enabling efficient oxygen reduction reaction

Rationally regulating the coordination environment of single-atom catalysts (SACs) is crucial for upgrading intrinsic catalytic activity and accelerating reaction kinetics. Herein, we present a facile bidentate pre- coordination-assisted pyrolysis strategy to tailor the first-shell coordination of carbon-based cobalt SACs, significantly boosting oxygen reduction reaction (ORR) activity. Specifically, asymmetric low-coordinated Co-N-3 and symmetric Co-N-4 moieties, atomically dispersed on N-doped carbon matrixes supported by carbon nanotubes (denoted Co-N-3-C/CNT and Co-N-4-C/CNT, respectively), are judiciously crafted by pre-anchoring Co atoms with a single bidentate ligand (phenanthroline-functionalized covalent organic polymer, Phen-COP) or dual bidentate ligands (Phen-COP and 2,2 '-bipyridine), followed by high-temperature pyrolysis. Notably, Co-N-3-C/CNT manifests outstanding ORR activity in alkaline media, achieving an onset potential of 1.044 V and a half-wave potential of 0.887 V, surpassing Co-N-4-C/CNT, Pt/C, and most state-of-the-art SACs. More importantly, combined experimental and computational investigations reveal that the asymmetric low-coordinated configuration of Co- N-3 disrupts the symmetric charge distribution of Co-N-4, facilitating oxygen activation and enabling an energy- favorable adsorption/desorption pathway for ORR-relevant intermediates. Consequently, zinc-air batteries with Co-N-3/CNT air cathode demonstrate a superior maximum power density of 159.3 mW cm(-2) and a high specific capacity of 892.6 mA h g(-1). This work provides atomic-level insights into designing high-performance SACs for efficient ORR electrocatalysis.