Brush-electroplated rGO@MnO2 composite supported on carbon cloth for flexible high-performance supercapacitor electrodes

With the emergence of intelligent society, high energy density and safety of flexible capacitive energy storage units are increasingly important in wearable devices. MnO2 as a flexible supercapacitor electrode material possesses the merits of high theoretical specific capacitance, low cost, and environmental friendliness. However, its poor conductivity, fragility, and low utilization hinder large-scale practical application. The rGO has excellent properties due to its unique sp2-hybridized carbon atom monolayer, such as high strength and high electrical conductivity. MnO2 can improve its own conductivity and specific capacitance by compounding with rGO. Both MnO2 and rGO can cooperate with each other to play their respective advantages and achieve a win-win situation. Herein, a facile brush electroplating technology is developed to fabricate flexible electrode materials composed of reduced-graphene oxide (rGO)@MnO2 composites grown on carbon cloth (CC) (denoted as rGO@MnO2/CC). A flexible rGO@MnO2/CC electrode prepared in an electrolyte with a rGO content of 1.0 g L-1 (denoted as 1.0-rGO@MnO2/CC) achieves high mass, area, and volume specific capacitances of 267 F g(-1), 400 mF cm(-2), and 13.3 F cm(-3), respectively, at a charge-discharge rate of 0.25 A g(-1). This is mainly due to the nanoporous structure formed by rGO and MnO2 nanosheets, which has higher electrical conductivity and good interfacial bonding. The rGO@MnO2/CC//active carbon (AC)/CC flexible aqueous asymmetric supercapacitor possesses a high energy density of 27.7 Wh kg(-1) at a power density of 250 W kg(-1) (0.9 mA cm(-2)) and a good capacitance retention of 76% after 10,000 charge-discharge cycles at a charge-discharge current density of 17.5 mA cm(-2) (5 A g(-1)). This study provides a novel facile method for the large-scale fabrication of high-performance flexible aqueous supercapacitors.