Construction of sp3/sp2 carbon interface in 3D N-doped nanocarbon for the oxygen reduction reaction.

The development of highly efficient metal-free carbon electrocatalysts for the oxygen reduction reaction (ORR) is one very promising strategy for the exploitation and commercialization of renewable and clean energy, but this still remains a significant challenge. Herein, we demonstrate a facile approach to prepare three-dimensional (3D) N-doped carbon with a sp(3)/sp(2) carbon interface derived from ionic liquids via a simple pyrolysis process. The tunable hybrid sp(3) and sp(2) carbon composition and pore structures stem from the transformation of ionic liquids to polymerized organics and introduction of a Co metal salt. Through tuning both composition and pores, the 3D N-doped nanocarbon with a high sp(3)/sp(2) carbon ratio on the surface exhibits a superior electrocatalytic performance for the ORR compared to that of the commercial Pt/C in Zn-air batteries. Density functional theory calculations suggest that the improved ORR performance can be ascribed to the existence of N dopants at the sp(3)/sp(2) carbon interface, which can lower the theoretical overpotential of the ORR.