Developing nonprecious electrocatalysts operating in acidic and alkaline media for an oxygen reduction reaction (ORR) is essential for sustainable energy technologies. Increasing the metal active site density is an effective strategy to enhance the activity, but it remains challenging because of metal sintering during pyrolysis. Here, we report a novel strategy of enriching atomically dispersed cobalt species in nitrogen-doped carbon for improving the electrocatalytic performance. A hollow carbon nanosphere with reduced shell thickness was obtained by taking advantage of the carbothermic reaction between carbon and ZnO template, and the resulting cobalt enrichment in the ultrathin carbon shell leads to an increase of the density of Co atoms. Together with advantageous microstructure features such as high surface area and multiscale porosity, the corresponding catalyst demonstrated promising oxygen reduction reaction performance in strong acidic and alkaline electrolytes and has two times higher kinetic current density than the nonenriched one. The present work provides an attractive and facile route to engineer active site in electrocatalysts.
Keywords: atomic cobalt enrichment; carbothermic reaction; electrocatalysis; oxygen reduction reaction; porous carbon shell.