A facile fabrication of MnO2/graphene hybrid microspheres with a porous secondary structure for high performance supercapacitors

MnO2/graphene nanosheets (MnO2/GNs) hybrid composite can be prepared by spray-drying technique with either graphene oxide (GO) or hydrazine-reduced graphene as precursor. The characterization results of the as-synthesized composites indicate that MnO2 and GNs are uniformly distributed and intertangled forming porous microspheres in a diameter of 2–4 μm. This special secondary structure is beneficial for an intimate contact between MnO2 and GNs accounting for improved conductivity. In addition, the high surface area and abundant porosity enables aqueous electrolyte to penetrate deeply inside the hybrid microspheres, and facilitating the Na+ insertion/release process, which increases the utilization of active component resulting in enhanced supercapacitance. MnO2/graphene hybrid microspheres exhibit a good cycling performance as the intertangled graphene buffers the volume change of MnO2 during charge–discharge cycles.