Single Co Atoms Implanted into N-Doped Hollow Carbon Nanoshells with Non-Planar Co-N4-1-O2 Sites for Efficient Oxygen Electrochemistry.

Facile synthesis of cost-effective carbon-supported Co single atoms (Co-SAs) exhibits huge potential applications in energy storage and conversion devices. We here report the implantation of Co-SAs into hollow carbon spheres (Co-SAs-HCS) via a facile wet-chemistry strategy followed by controlled pyrolysis. Electron-rich histidine acted as a Lewis base effectively immobilizing Co2+ (Lewis acid) via the electrostatic effect and hydrogen bonds, thus achieving the scalable synthesis of Co-SAs-HCS. We constructed a series of histidine-Co2+ structure models to elucidate the formation of histidine-Co2+ complexes by analyzing their binding energy. X-ray absorption fine-structure results verify that central Co atoms with four N coordination atoms possess a non-planar Co-N4 structure. Electrochemical results indicate that the as-prepared Co-SAs-HCS catalyst shows a low potential difference (0.809 V) between the oxygen evolution reaction potential at 10 mA cm-2 and the oxygen reduction reaction half-wave potential, outperforming the commercial Pt/C catalysts (0.996 V). Moreover, an assembled Zn-air battery based on Co-SAs-HCS exhibits an unexpected long-term durability. We have demonstrated that non-planar Co-N4-1-O2 sites are the source for highly efficient adsorption and dissociation of O2 molecules and then reduction of the free energy of desorption of the intermediates by density functional theory. Our findings provide a new design insight into the exploration of advanced electrocatalysts, which will be applied in the design of green energy devices in the future.