The synthesis of shape-controlled MnO₂/graphene composites via a facile one-step hydrothermal method and their application in supercapacitors

Novel MnO₂ petal nanosheet and nanorod/graphene composites are successfully fabricated by a facile one-step hydrothermal method through changing the content of the Mn source. The formation mechanism of different morphologies of MnO₂/graphene composites have been studied. The structure of the MnO₂/graphene is "sandwich"-like, with MnO₂ petal nanosheets and nanorods homogeneously anchored on each side of the graphene. Furthermore, the MnO₂/graphene composites with different shapes can be used for supercapacitor electrode materials. The experimental results show that the MnO₂ petal nanosheet/graphene composite has better capacitance performance than that of the MnO₂ nanorod/graphene composite. The MnO₂ petal nanosheet/graphene composite shows excellent specific capacitance as high as 516.8 F g^-1 at a scan rate of 1 mV s^-1 in 1 M Na₂SO₄ electrolyte and good long-term cycle stability, indicating its potential application to act as a promising electrode material for high-performance supercapacitors. This study provides a facile and in situ method to prepare metal oxide/graphene composite materials and a novel scaffold to construct other metal oxides with graphene for energy storage.