•We study the ZnO and Carbon coated ZnO nanoparticles for supercapacitor electrode materials.•Initially pure ZnO and ZnO/C nanoparticles were measured for three electrode configuration.•This result indicates that carbon coated ZnO nanoparticles is the suitable candidate for symmetric supercapacitor device fabrication.•Based on these three electrode results we fabricated on symmetric device.•The symmetric device yields a specific cell capacitance of 92 F g−1 at the specific current of 2.5 A g−1. With the eco friendly green chemistry technique in mind, sucrose has been used in this study as the capping agent to synthesize ZnO/C nanocomposite adapting sol-gel method. The presence of carbon in the prepared ZnO/C was confirmed through EDAX. Electrochemical investigations of ZnO/C electrode were carried out using cyclic voltammetry, galvanostatic charge-discharge, and electrochemical impedance spectroscopy. The ZnO/C electrode exhibits a maximum specific capacitance of 820 F g−1 at a constant specific current of 1 A g−1. The symmetric aqueous supercapacitor device exhibits the specific cell capacitance of 92 F g−1 at the specific current of 2.5 A g−1. The aqueous symmetric supercapacitor device achieved an energy density of 32.61 Wh kg−1 and the power density of approximately 1 kW kg−1 at a discharge current of 1.0 A g−1. It has been found that the cells have an excellent electrochemical reversibility (92% after 400 continuous cycles) and capacitive characteristics in 1 M Na2SO4 electrolyte.