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.