Facile synthesis of Co, N enriched carbon nanotube and active site identifications for bifunctional oxygen reduction and evolution catalysis

Abstract The carbon-based electrocatalyst for rechargeable zinc-air battery not only needs bifunctional activities to oxygen reduction and evolution reactions, but also requires a high graphitization degree to maintain an excellent stability. Herein, a simple and scale-up strategy is developed to synthesize a highly active and stable electrocatalyst (Co@N-CNT) through a solid-state thermal conversion process, derived from a single and easy-to-get precursor (cobaltic Prussian blue analogue). The Co particles trapped inside the tips are the growth sites of the carbon nanotubes and greatly improve the catalytic activity. This kind of special structure helps Co@N-CNT to achieve remarkable bifunctional activities comparable to the noble metal counterparts and superior durability. Interestingly, Co@N-CNT is proved to have no single-atom Co sites on the carbon nanotube. In combination with electrochemical tests, X-ray absorption spectroscopy and theoretical calculations, Co@graphitic N-C is considered to be the best ORR active site while Co@pyridinic N-C is the best OER active site.