Extrinsic Pseudocapacitive NiSe/rGO/g-C₃N₄ Nanocomposite for High-Performance Hybrid Supercapacitors

Battery-type materials with ultrahigh energy density show great potential for hybrid supercapacitors (HSCs). In this work, we have developed a nickel selenide (NiSe)/reduced graphene oxide (rGO)/graphitic carbon nitride (g-C₃N₄) ternary composite as a promising positive electrode for hybrid supercapacitors (HSCs). The extended π-conjugated planar layers of g-C₃N₄ promote strong interconnectivity with rGO, which further enhances surface area, surface free energy, and efficient electron/ionic path. Additionally, it establishes clear ion diffusion pathways, serving as ion reservoirs during charge and discharge and facilitating efficient redox reactions. As a result, the NiSe/g-C₃N₄/rGO nanocomposite electrode displayed a specific capacity of 412.6 mA h g^-1 at 1 A g^-1. Later, the HSC device was assembled using the nanocomposite as the positive electrode and activated carbon as the negative electrode, which delivered an energy density of 65.2 Wh kg^-1 at a power density of 750 W kg^-1. Notably, the HSC device maintained excellent cyclic stability, preserving 93.3% of its initial performance and Coulombic efficiency of 86.6% for 10,000 charge-discharge cycles at 5 A g^-1. These findings underscore the potential utility of NiSe/g-C₃N₄/rGO as a versatile and effective electrode material for the strategic development of HSC devices.