Development of Boron-Doped Nickel Zinc Oxide Electrodes for Efficient Energy Storage in Asymmetric Supercapacitors

The Ni0.6Zn0.4O/ZnO (NZO) and three boron-doped composites (BNZO-1, BNZO-2, and BNZO-3) were synthesized via a hydrothermal method at 160 °C for 8 h. X-ray diffraction (XRD) confirmed the presence of Ni0.6Zn0.4O, ZnO, and successful boron doping in the crystal structure. Raman spectroscopy identified Ni–O and Zn–O bonds in all NZO composites. Field emission scanning electron microscopy (FESEM) revealed flake-like and rod-like morphologies for Ni0.6Zn0.4O/ZnO and boron-doped Ni0.6Zn0.4O/ZnO, respectively. Among the BNZO composites, BNZO-2 demonstrated the highest electrochemical performance, with a specific capacitance of 718 F g–1 at a current density of 1 A g–1. The asymmetric device constructed with g-C3N4 as the negative electrode and BNZO-2 as the positive electrode (g-C3N4//BNZO-2) achieved a specific capacitance of 40 F g–1 at a current density of 1 A g–1. Additionally, the device exhibited outstanding long-term stability, maintaining a substantial proportion of its capacitance after 4000 charge–discharge cycles. It also demonstrated high Coulombic efficiency, highlighting its potential for energy storage applications.