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 degrees 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.