Hollow carbon nanoparticles derived from Co₃O₄/carbon black hybrid: solid-phase synthesis and applications in a Zn-air battery

Metal-free carbon materials are regarded as a promising catalyst for the oxygen reduction reaction (ORR), owing to their high activity in an alkaline environment. In this paper, using industrial carbon black-supported Co₃O₄ hybrid as a raw material, typical hollow carbon nanoparticles were synthesized by solid-phase annealing the hybrid at an elevated temperature, followed by HCl etching to remove the cobalt oxide. The specific surface area of the hollow carbon is significantly increased and the total nitrogen content of the carbon is 4.13 at%, providing massive active sites for ORR. In alkaline solution, compared with the commercial Pt/C, the nitrogen-doped hollow carbon nanoparticles display a superior ORR electrocatalytic activity with a half-wave potential of 0.88 V versus the reversible hydrogen electrode. Furthermore, the catalyst exhibits an excellent stability and high discharge power density in the Zn-air battery. This study provides a simple and feasible strategy of solid-phase synthesis for the production of high performance metal-free hollow carbon materials.