Mixed-valence manganese oxide/reduced graphene oxide composites with enhanced pseudocapacitive performance

As typical pseudocapacitive materials, manganese oxides have attracted great interest due to their high theoretical specific capacitance, abundant oxidation states and crystal structures. However, it is still struggling from inferior electrical conductivity, which comes from their natural properties and limited structure used. In this paper, we fabricate hierarchical mixed-valence manganese oxide/graphene on flexible carbon cloths via a hydrothermal method combined with annealing treatment strategy for improving capacitive performance. The microstructure and electrochemical performance of manganese oxide/reduced graphene oxide (MnOx/G) electrodes obtained at different annealing temperature (400–700 °C) are investigated. Evidenced by XRD, XPS and TEM, MnOx/G composites consisted of α-MnO2, hexagonal Mn2O3 and cubic MnO are achieved as the annealing temperature increased. The results reveal that the phase of MnOx, valence state of Mn as well as the pseudocapacitance can be regulated by varying the annealing temperature, and the mixed-valence state in the MnOx/G-400 composite boost pseudocapacitive property significantly. The MnOx/G-400 electrode yields the highest areal capacitance of 2.29 F cm−2 (437 F g−1) and remarkable stability compared to other MnOx-based electrodes, which is attributed to the favored electron transfer between Mn species (Mn4+ ↔ Mn3+), decreased charge transfer resistance and more active sites between different phase interfaces. This work reports the synthesis of hierarchical mixed-valence manganese oxide/reduced graphene oxide composites on flexible carbon cloths via a hydrothermal method combined with annealing treatment strategy for improving capacitive performance.