Synergistic effects of Ag nanoparticles in the rGO and Co3O4 based electrode materials for asymmetric supercapacitors

Abstract

A systematic investigation of the composite electrode materials is vital in fabricating supercapacitors with high specific capacitance and good stability. The present work systematically studies the synergistic effects of Ag nanoparticles (AgNPs) on the electrochemical behaviour of rGO-based supercapacitor anode and Co3O4/rGO composite cathode. The Co3O4/(Ag/rGO) composite has been fabricated by hydrothermally growing Co3O4 nanoparticles over the previously prepared Ag/rGO support in the 70:30 ratio. The electrochemical performance of fabricated electrodes was evaluated by cyclic voltammetry (CV) and galvanostatic charge-discharge (GCD) in 1 M KOH electrolyte. The Ag/rGO electrode having 15 - 20 % of AgNPs displays a specific capacitance of 553.6 F/g by CV (@10 mV/s) and 449.4 F/g by GCD (@0.35 A/g), which is 2.9 – 3.1 times higher than pristine rGO, when scanned in the range of – 1.0 V - 0.0 V (Vs. Ag/AgCl). The Co3O4/(Ag-20/rGO) composite electrode (in the ratio 70:30) possesses 244.9 F/g of specific capacitance (by GCD @3.8 A/g in the range of – 0.2 V - 0.5 V (Vs. Ag/AgCl)), which is 3.2 and 2.0 times higher than Co3O4 and Co3O4/rGO respectively. The Co3O4, Co3O4/rGO and Co3O4/(Ag/rGO) samples retained 67 % (at 3.8 A/g), 91 % (@1.4 A/g), and 82 % (@1.4 A/g) of specific capacitance after 2000 cycles. The asymmetric supercapacitor device in rGO||Co3O4/Ag/rGO configuration shows an initial specific capacitance of 438.0 F/g, energy and power densities of 38.9 Whkg‒1 and 640 Wkg‒1, respectively, at 2 A/g current density. The demonstrated boost in performance arises due to the presence of Ag nanoparticles leading to enhanced conductivity, catalyzing the pseudocapacitive reactions and preventing the graphene layers from aggregation by acting as spacers, spacers, thus making Ag/rGO and Co3O4/Ag/rGO as potential electrode materials for asymmetric supercapacitors.