Understanding the Impact of the Morphology, Phase Structure, and Mass Fraction of MnO2 within MnO2/Reduced Graphene Oxide Composites for Supercapacitor Applications

The electrochemical supercapacitor performance of MnO2 is significantly influenced by the phase structure due to the various structural features of the different MnO2 polymorphs that include tunnels or layered structures that can facilitate ion transport and intercalation. However, the effect of the crystal structure of MnO2 within MnO2/carbon composites has not been fully explored or understood. Herein, we have synthesized different crystal structures of MnO2 (α- and β-MnO2) within MnO2/reduced graphene oxide (rGO) composites by a hydrothermal process using various amounts of (NH4)2SO4, followed by systematic structural characterization and electrochemical capacitance measurements. An excellent capacitance performance of 403 F g–1 was observed in α-MnO2/sulfur and nitrogen codoped reduced graphene oxide (S,N-rGO) composites because of the interconnection between the conductive porous 3D architectures of S,N-rGO and the α-MnO2 nanorods. This work highlights how the morphology, phase structure, and mass loading of MnO2 within MnO2/rGO composites directly influence the capacitance performance and rate capabilities, which provides insight into the design of MnO2-based composite materials for supercapacitor applications.