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

Abstract

Development\nof next-generation electrode materials for battery-like\nsupercapacitors has paid unique impetus from both energy density and\npower density perspectives. This report provides a facile synthetic\nroute for the preparation of nickel–cobalt oxalate (NiCo₂C₂O₄). The material exhibits a specific\ncapacitance (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,\nwhere the sheet-kind NiCo₂C₂O₄ was\nuniformly decorated onto the graphitic carbon nitride (g-C₃N₄) thin sheets. Interestingly, the developed nanoporous\nNiCo₂C₂O₄/g-C₃N₄ composite delivers a high specific capacitance (specific capacity)\nof 1263 F g^–1 (158 mAh g^–1) at\n1 A g^–1. In addition, the nanoporous composite network\nshowed a high specific energy of about 35.54 Wh kg^–1 at the specific power of 226.36 W kg^–1. The electrochemical\nstudies unveil that the materials stored charge through both surface\nredox and intercalation redox (battery-like) processes. The higher\nspecific capacity of the composite could be attributed to the synergistic\ncoupling between Ni and Co ions, high oxygen defect content, and the\nimproved redox process of Ni/Co ions facilitated by the g-C₃N₄ support. In addition, a hybrid device was developed\nusing NiCo₂C₂O₄/g-C₃N₄ and activated charcoal (AC) as positive and negative electrodes,\nrespectively. The hybrid device exhibited an extended voltage window\nof 1.5 V, and a good rate capability along with a maximum specific\nenergy value of 18.4 Wh kg^–1 at the specific power\nvalue of 732 W kg^–1.