Template-free synthesis of polyacrylonitrile-derived porous carbon nanoballs on graphene for efficient oxygen reduction in zinc–air batteries

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.