Synergistic effects in rGO/Co3O4/PPy//rGO/CuO electrodes for high-performance asymmetric supercapacitors

Abstract

Abstract Supercapacitors exhibit several fundamental advantages, including fast ion-transport, high charge–discharge capability, and high power density. In this study, an asymmetric supercapacitor configuration was designed in which a reduced graphene oxide (rGO), cobalt (II, III) oxide (Co 3 O 4 ), and polypyrrole (PPy) composite was employed as the positive ( +) electrode (cathode) deposited on aluminum foil, while an rGO/copper (II) oxide (CuO) composite served as the negative (-) electrode (anode) on copper foil. The cathode electrodes were prepared with initial feed ratios of [rGO] o /[Co 3 O 4 ] o /[Py] o = 1:5:1, 1:5:2, 1:5:5 and 1:5:10. Furthermore, the anode electrode was designed using rGO-supported doped CuO as the active material with a feed ratio of [rGO] o /[CuO] o = 1:1. The assembled electrodes were integrated into CR2032 coin cells to construct the asymmetric supercapacitor device. The characterization of the cathode electrode active materials has been reported in our previous study. Therefore, only the characterization of the anode electrode material is presented here, including BET, TGA-DTA SEM–EDX and FTIR-ATR analyses. An ionic liquid electrolyte was employed in the supercapacitor device to enhance the operating voltage window, as evidenced by the galvanostatic charge–discharge (GCD) measurements. The asymmetric rGO/Co 3 O 4 /PPy//rGO/CuO supercapacitor exhibited the highest specific capacitance for the electrode composition with an initial feed ratio of [rGO] o /[Co 3 O 4 ] o /[Py] o = 1:5:2. A specific capacitance of 1380 F/g was obtained at a scan rate of 2 mV/s using cyclic voltammetry (CV) method, while a value of 181.48 F/g was achieved at a current density of 10 A/g from GCD measurements. This superior electrochemical performance is further corroborated by the highest areal and volumetric capacitance values C A = 45.37 F/cm 2 and C V = 4537.04 F/cm 3 , respectively, measured at 10 A/g for the same composition. The capacitance retention of the asymmetric supercapacitor reached 89.1% for the electrode composition with an initial feed ratio of [rGO] o /[Co 3 O 4 ] o /[PPy] o = 1:5:10 after 1000 charge–discharge cycles, as evaluated by CV in a CR2032 coin cell. Moreover, the highest energy density was calculated to be E = 78.13 Wh/kg at a current density of 1 A/g. This performance is further supported by electrochemical impedance spectroscopy (EIS) results, which yielded a specific capacitance ( C s p ) of 0.283 F/g and a double-layer capacitance ( C dl ) of 0.129 F/g for the same composition. Overall, the newly designed asymmetric rGO/Co 3 O 4 /PPy//rGO/CuO electrode configuration demonstrates strong potential as an effective candidate for advanced supercapacitor applications.