Abstract
Transition metal vanadates have sparked much attention as positive electrode materials for supercapacitors; nevertheless, their poor electronic conductivity, low electroactive sites, and sluggish charge transfer kinetics continue to be problematic. Herein, we incorporate Co dopants in nickel vanadates (NCV) and successfully tailor porous 3D oval-shaped particles using hydrothermal synthesis at 210 degrees C for 12 h. The interconnected particles, as well as the porous nature of each oval-shaped particle, provide high accessibility to active species and improve charge transfer kinetics. Additionally, the incorporation of cobalt dopants improves electronic conductivity and enriches redox chemistry. As a consequence, NCV delivered a specific capacitance of 391/376 F/g at 0.5/1 A/g current density, with capacitance retention of 98.6 % after 8000 cycles, indicating outstanding cycling stability. Moreover, the micro-spherical layered-structured BiOBr electrode was chosen for the negative electrode and demonstrated a specific capacitance of 132 F/g at a current density of 1 A g-1, in the potential window of -1 to +0 V. Furthermore, the solid-state Ni3-xCoxV2O8//BiOBr hybrid supercapacitor device demonstrated 118 F/g specific capacitance, 25.5 Wh kg-1 energy density, and exceptional cycle stability (85.9 % capacitance preserved after 10,000 cycles).