▎ 摘　　要

Introducing abundant active sites and improving their activity are two critical considerations for designing metal-free nitrogenous electrocatalysts for the oxygen reduction reaction (ORR) in energy conversion devices such as metal-air batteries and fuel cells. In this study, we have developed nitrogenous carbon nanoballs with edge-abundant graphitic nitrogen (N) which were derived from polyacrylonitrile (PAN) on reduced graphene oxide (PANRGO). Upon carbonization, PAN promotes the generation of a carbon nanoball-like structure with defective edges and a hollow structure on graphene (PANRGO-700) without any template which substantially enhances the ORR kinetics by increasing the activity and accessibility of active sites. Consequently, the PANRGO-700 catalyst exhibits a high ORR catalytic activity compared to Pt/C by displaying a higher half-wave potential and kinetic current density of 0.864 V and 32.6 mA cm(-2), respectively, in 0.1 M KOH. Further, its superiority as the cathode electrode was confirmed in a home-made Zn-air battery with producing a comparable power density of 116.6 mW cm(-2).