Redox-active Co₃O₄/MgV₂O₅ heterostructure with abundant reaction sites for aqueous asymmetric supercapacitor: Insight into charge storage capacity via Dunn's modeling

Batteries and supercapacitors are promising energy storage devices to meet the current demand of energy storage demands. Unfortunately, batteries do not retain high cyclic performance as well as power density. On the other hand, supercapacitors retain high cyclic stability but less energy density. Benefiting from the charge storage mechanism of these two devices, the composite material of transition oxide and vanadate is proposed to boost up the specific capacity power density and cyclic stability. Due to the high theoretical capacity of cobalt oxide and high conductivity of magnesium vanadate is selected as the key component materials of composite material. The formation of material composition is confirmed by using the X-ray diffraction technique and tunneling electron microscopy which revealed the successful heterostructure. The morphological assessment revealed that highly dispersed cobalt oxide in magnesium vanadate flakes leads to the increase in overall capacitance (495 C/g) of the composite material in comparison with the Co₃O₄ and MgV₂O₅ which shows 88 C/g and 43 C/g at 1 A/g Current density respectively. Further, the cooperation of cobalt oxide led to improved EDLC behavior thus improving the power density. The highest specific capacity may be due to the shorter diffusion time (0.09 s) of ionic species for intercalation into electrode material. Moreover, highly dispersed cobalt oxide in magnesium vanadate provides more reaction sites due to the presence of multi-redox species with different valence states (Co⁺³, Co⁺⁴, Mg⁺³, Mg⁺⁴) and high surface area which results in high specific capacitance. Moreover, the fabricated prototype device demonstrates an excellent power density of 13200 W/kg at 5 A/g. Also, the device can successfully deliver 8.9 Wh/kg with 92 % coulombic efficiency and 90 % cyclic retention after 2000 cycles. The fabricated Co₃O₄/MgV₂O₅//AC device operated the commercial calculator, indicating the practical viability of the device.