Asymmetric Supercapacitors Based on ZnCo₂O₄ Nanohexagons and Orange Peel Derived Activated Carbon Electrodes

Herein, the performance of asymmetric supercapacitors (ASC) fabricated using ZnCo₂O₄ (ZCO) nano-hexagons and orange peel-derived activated carbon (OPAC) as electrodes was studied. ZCO was prepared by a double hydroxide method and OPAC was prepared from orange peel followed by KOH activation. For ZCO, the calcination temperature was determined using TGA analysis. The XRD showed the presence of a cubic spinel structure. The chemical structure was analyzed using XPS, FTIR, and Raman spectroscopy respectively. For OPAC, the presence of an amorphous nature was inferred; FTIR and Raman studies indicate the presence of functional groups and defect structure in the material. The presence of ZCO nano-hexagons was observed from SEM and TEM respectively. For OPAC, an interconnected pore structure was observed from the SEM image. The specific capacitance for ZCO and OPAC was found to be 194 F.g^-1 and 159 F.g^-1 at a current density of 0.25 A.g^-1. Further, an ASC was fabricated using ZCO as a positive and OPAC as a negative electrode in 2M KOH-soaked separator. A cell voltage of 1.2 V was achieved and the specific capacitance was calculated to be 64 F.g^-1 at 0.25 A.g^-1. Further, the cyclic stability and the changes at the electrode/electrolyte interface were studied.