Tailoring Atomically Dispersed Co-N4 Sites with Edge Enrichment Boost Excellent Oxygen Reduction Performance

Atomically-dispersed transition-metal nitrogen-carbon catalysts with specific coordination structures are promising low-cost candidates for efficient oxygen reduction reaction (ORR) in metal-air and fuel cells. However, a large part of internal active sites in this class of catalysts cannot really take effect, and the density of edge active sites is seriously insufficient. Here we designed a reasonable edge-host stepwise method involving adsorption and pyrolysis to prepare Co-Nx/C-NC electrocatalysts with highly-dispersed active sites at the edges, and to stabilize the isolate atomically-dispersed Co-NX sites on the surface of graphitized N-doped carbon (NC). The new catalysts achieved admirable ORR activity with half-wave potential (E1/2) of 0.883 V under alkalinity. Moreover, Co-Nx/C-NC showed stronger four-electron transfer ability and much higher stability (only 6 mV loss of E1/2 after 5000 cycles). The main reason was that the coordination environment and density of active sites were effectively optimized, enabling the increase of edge active sites and reactivity. This work provides a general approach for design and preparation of highly-stabilized and abundant atomically-dispersed edge-active-sites for production in electrochemical energy devices.