Electrostatic self-assembly deposition of manganese dioxide nanosheets on functionalized graphene sheets as supercapacitor electrode

Functionalized graphene was synthesized via the reduction of graphene oxide with poly(diallyldimethylammonium chloride) (PDDA). This reduced graphene oxide (RGO) changed from a negative to a positive charge. The negatively charged MnO2 nanosheets were then anchored on the positively charged surface of the PDDA- functionalized RGO (PFRGO) sheet by electrostatic self-assembly deposition. The strong interactions between the MnO2 nanosheet and the PFRGO sheet form a face-to-face assembly structure, which maximizes the exposure of MnO2 redox-active sites and accelerates charge transfer between the two components. The resulting MnO2-PFRGO composite electrode exhibits a high specific capacitance of 175 F g−1, which was increased by 52% relative to pristine MnO2. Moreover, the equivalent series resistance (ESR) value of the composite (0.66 Ω) is over two-times smaller than pristine MnO2. The capacitance retention is 88.8% after 5000 charge–discharge cycles, demonstrating good cycling stability.