Abstract

Graphitic carbon nitride (g-C3N4) contains a high C/N ratio of 3/4; however, utilizing nitrogen atoms in pseudocapacitive energy storage systems remains a challenge due to the limited number of edge nitrogen atoms and inherent poor electrical conductivity of this semi-conductor material. 3D oxidized g-C3N4 functionalized graphene composites (GOOCN24), in which reduced graphene oxide providing high electron conductivity acts as a skeleton and hybridises with oxidized g-C3N4 segments, were synthesized using a facile two-step solution-based method. Due to the pre-oxidation treatment of g-C3N4, which breaks the polymeric nature of g-C3N4 and increases in the proportion of edge nitrogen atoms and the subsequent solubility in water, the GOOCN24 composites used as electrodes for supercapacitors show a specific capacitance as high as 265.6 F g−1 in acid electrolyte and 243.8 F g−1 in alkaline electrolyte in three-electrode configuration at a current density of 1 A g−1. In addition, low internal resistance, excellent rate performance of over 74% capacitance retention (over a 50-fold increase in current density), and outstanding cycling stability of over 94% capacitance retention after 5000 cyclic voltammetry cycles in both alkaline and acid electrolytes was attained. This translated into excellent energy density with appropriate power density when demonstrated in a symmetrical device.