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

Abstract

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 ε-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 ε-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.