Facile synthesis of flower-like NiCo/NiO–CoO surrounded by N-doped porous carbon derived from covalent organic framework for aqueous asymmetric supercapacitor

Abstract

The persisting quest for improving charge density, electronic conductivity and cyclic stability of the electrode material in supercapacitor (SC) applications still demands intensive research and advancements. This study also aims the aforementioned pursuit with the construction of hybrid supercapacitor using mixed metal oxides with the incorporation of metal and supported with porous carbon to improve the charge density, electrical conductivity and cyclic stability, respectively. A covalent organic framework (COF) was synthesized and doped with nickel (Ni2+) and cobalt (Co2+) ions followed by carbonization at 1000 °C for 3 h to generate NiCo/NiO–CoO surrounded N-doped porous carbon (NPC) framework. The X-ray diffraction reveals that nickel considerably impacts the crystallinity of NiCo/NiO–CoO and the Raman spectroscopy revealed that the NiCo/NiO-CoO-NPC with an equal molar ratio of Ni2+ and Co2+ ions (NiCo/NiO-CoO-NPC-2) offered the highest degree of graphitization. The electron microscopic images showed the formation of flower-like morphology of NiCo/NiO-CoO-NPC-2 with a size of 250 nm and the greater number of flowers on NPC's surface could augment the electrochemical activity of the composite material. The NiCo/NiO–CoO-NPC-2 offered an attractive specific capacitance (Cs) of 845 F g−1 @ 1 A g−1 and preserves 93% capacity retention @ 10 A g−1 after 6000 charge-discharge cycles while exploited in SC application. The metal-free COF carbonized at 900 °C (CCOF-900) is utilized as the negative electrode with a Cs of 286 F g−1 @ 1 A g−1 for the construction of an asymmetric supercapacitor device and the NiCo/NiO-CoO-NPC-2//CCOF-900 device delivered efficient energy of 54 Wh kg−1 at a power density of 633 W kg−1.