Controllable in situ synthesis of epsilon manganese dioxide hollow structure/RGO nanocomposites for high-performance supercapacitors

Well-organized epsilon-MnO2 hollow spheres/reduced graphene oxide (MnO2HS/RGO) composites have been successfully constructed via a facile and one-pot synthetic route. The e-MnO2 hollow spheres with the diameter of ∼500 nm were grown in situ with homogeneous distribution on both sides of graphene oxide (GO) sheets in aqueous suspensions. The formation mechanism of the MnO2HS/RGO composites has been systematically investigated, and a high specific capacitance and good cycling capability were achieved on using the composites as supercapacitors. The galvanostatic charge/discharge curves show a specific capacitance of 471.5 F g−1 at 0.8 A g−1. The hollow structures of e-MnO2 and the crumpled RGO sheets can enhance the electroactive surface area and improve the electrical conductivity, thus further facilitating the charge transport. The MnO2HS/RGO composite exhibits a high capacitance of 272 F g−1 at 3 A g−1 (92% retention) even after 1000 cycles. The prominent electrochemical performance might be attributed to the combination of the pseudo-capacitance of the MnO2 nanospheres with a hollow structure and to the good electrical conductivity of the RGO sheets. This work explores a new concept in designing metal oxides/RGO composites as electrode materials.