Highly sp2 hybridized and nitrogen, oxygen dual-doped nanoporous carbon network: Synthesis and application for ionic liquid supercapacitors

Abstract

The utilization of ionic liquids as electrolyte is beneficial for realization of high energy density supercapacitors due to their high operation voltage. Nevertheless, ionic liquids electrolytes suffer from sluggish ion diffusion and poor wetting behavior on porous electrodes as a result of large ion sizes and high viscosity, which has severely hindered their practical use. Herein, highly sp2 hybridized and nitrogen, oxygen dual-doped nanoporous carbon networks were prepared based on charge-induced self-assembly strategy using chitosan as carbon precursor with reduced graphene oxide (GO) in between as conductive scaffolds. The optimized material as supercapacitor electrodes exhibits an outstanding specific capacitance of 201 F g−1 in 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIMBF4) electrolyte at 0.5 A g−1 with a maximum energy density of 111 Wh kg−1, superior to numerous reported values, which are attributed to multiple synergistic effects of several beneficial characteristics, that is, excellent conductivity deduced from highly sp2 hybridized carbon originated from carbonized chitosan and graphene conductive scaffolds being in favor of rate performance and cyclic stability, nitrogen and oxygen functionalization improving the surface wettability with electrolyte as well as contributing to the capacitance, large specific surface areas providing abundant active sites to boost charge capacity, and sheet-like structures effectively shortening diffusion pathways to improve ion transports.