Nitrogen-doped and reduced graphene oxide scrolls derived from chemical exfoliation of vapor-grown carbon fibers for electrochemical supercapacitors

Abstract

Vapor-grown carbon fibers with partially disordered graphitic structure allow for the formation of graphene oxide scrolls (GOSs) through a solution-based chemical exfoliation along their longitudinal directions. Heat treatment of GOS at 300 °C in an air atmosphere forms the partially reduced GOS (denoted as HT-RGOS) with curved and hydrophobic graphene oxide sheets. Hydrothermal treatment of GOS in urea solution results in the formation of N-doped and reduced GOS (denoted as N-RGOS) with more curved and hydrophilic surface than the HT-RGOS. The charge-storage behavior of HT-RGOS and N-RGOS electrodes in 1M KOH electrolyte is mostly dominated by the pseudocapacitive faradaic processes, while the GOS electrode is characterized by both the pseudocapacitive faradaic and non-capacitive processes. The specific capacitance of N-RGOS electrode reaches 228 F g−1 which is greater than that of GOS (77 F g−1) and HT-GOS (190 F g−1) electrodes at a current density of 1 A g−1. The improved supercapacitive behavior of N-RGOS results from the enhanced hydrophilicity and electrical conductivity by the introduction of nitrogenous groups to the N-RGOS that enable the easy transport of electrolyte and electron through the graphene scrolls.