Nanoporous Graphitic Carbon Nitride Nanosheets Decorated with Nickel–Cobalt Oxalate for Battery-Like Supercapacitors

Development of next-generation electrode materials for battery-like supercapacitors has paid unique impetus from both energy density and power density perspectives. This report provides a facile synthetic route for the preparation of nickel–cobalt oxalate (NiCo2C2O4). The material exhibits a specific capacitance (specific capacity) value of 1009 F g–1 (126 mAh g–1) at a current density of 1 A g–1. Further, the inclusion of g-C3N4 during the synthesis resulted in the formation of a nanoporous NiCo2C2O4/g-C3N4 composite, where the sheet-kind NiCo2C2O4 was uniformly decorated onto the graphitic carbon nitride (g-C3N4) thin sheets. Interestingly, the developed nanoporous NiCo2C2O4/g-C3N4 composite delivers a high specific capacitance (specific capacity) of 1263 F g–1 (158 mAh g–1) at 1 A g–1. In addition, the nanoporous composite network showed a high specific energy of about 35.54 Wh kg–1 at the specific power of 226.36 W kg–1. The electrochemical studies unveil that the materials stored charge through both surface redox and intercalation redox (battery-like) processes. The higher specific capacity of the composite could be attributed to the synergistic coupling between Ni and Co ions, high oxygen defect content, and the improved redox process of Ni/Co ions facilitated by the g-C3N4 support. In addition, a hybrid device was developed using NiCo2C2O4/g-C3N4 and activated charcoal (AC) as positive and negative electrodes, respectively. The hybrid device exhibited an extended voltage window of 1.5 V, and a good rate capability along with a maximum specific energy value of 18.4 Wh kg–1 at the specific power value of 732 W kg–1.