Tailoring Single-Atom Coordination Environments in Carbon Nanofibers via Flash Heating for Highly Efficient Bifunctional Oxygen Electrocatalysis.

The rational design of carbon-supported transition metal single-atom catalysts necessitates precise atomic positioning within the precursor. However, structural collapse during pyrolysis can occlude single atoms, posing significant challenges in controlling both their utilization and coordination environment. Herein, we present a surface atom adsorption-flash heating (FH) strategy, which ensures that the pre-designed carbon nanofiber structure remains intact during heating, preventing unforeseen collapse effects and enabling the formation of metal atoms in nano-environments with either tetra-nitrogen or penta-nitrogen coordination at different flash heating temperatures. Theoretical calculations and in situ Raman spectroscopy reveal that penta-nitrogen coordinated cobalt atoms (Co-N) promote a lower energy pathway for oxygen reduction and oxygen evolution reactions compared to the commonly formed Co-N sites. This strategy ensures that Co-N sites are fully exposed on the surface, achieving exceptionally high atomic utilization. The turnover frequency (65.33 s) is 47.4 times higher than that of 20 % Pt/C under alkaline conditions. The porous, flexible carbon nanofibers significantly enhance zinc-air battery performance, with a high peak power density (273.8 mW cm), large specific capacity (784.2 mAh g), and long-term cycling stability over 600 h. Additionally, the flexible fiber-shaped zinc-air battery can power wearable devices, demonstrating significant potential in flexible electronics applications.