Asymmetric Supercapacitors Based on Graphene/MnO 2 Nanospheres and Graphene/MoO 3 Nanosheets with High Energy Density

Asymmetric supercapacitors with high energy density are fabricated using a self‐assembled reduced graphene oxide (RGO)/MnO 2 (GrMnO 2 ) composite as a positive electrode and a RGO/MoO 3 (GrMoO 3 ) composite as a negative electrode in safe aqueous Na 2 SO 4 electrolyte. The operation voltage is maximized by choosing two metal oxides with the largest work function difference. Because of the synergistic effects of highly conductive graphene and highly pseudocapacitive metal oxides, the hybrid nanostructure electrodes exhibit better charge transport and cycling stability. The operation voltage is expanded to 2.0 V in spite of the use of aqueous electrolyte, revealing a high energy density of 42.6 Wh kg −1 at a…