Nanometric MnO₂ and MnO₂‐Graphene Oxide Materials Enabled by a Solvent‐Assisted Synthesis and Their Application in Asymmetric Supercapacitors

Abstract

Conventional manganese oxide (MnO 2 )‐based supercapacitors struggle to achieve theoretical capacitance due to the material's low conductivity and large particle size. Consequently, researchers have improved MnO 2 's properties by incorporating conductive carbonaceous materials to obtain high‐performance composite materials. Herein, the full process of engineering a MnO 2 ‐graphene oxide (GO) composite and its application as a positive electrode for asymmetric supercapacitors (ASC) is presented. First, GO using a novel gas expansion precursor allowing an efficient chemical exfoliation of pristine graphite is synthesized. Afterward, size‐weakened MnO 2 nanoparticles are synthesized and deposited onto the GO sheets by a self‐assembly redox reaction method using different MnO 2 /GO mass ratios. Multiple characterization methods are used to investigate the textural and structural properties of each material. A general electrochemical characterization is conducted using a three‐electrode cell; therefore, the synthesized MnO 2 ‐GO composite achieves 150 F g −1 at 10 mV s −1 . Furthermore, an ASC in an aqueous electrolyte using GO and MnO 2 or MnO 2 ‐GO as negative and positive electrodes, respectively, is assembled. The fabricated ASC based on MnO 2 ‐GO composite exhibits a high specific capacitance of 38 F g −1 at 1 A g −1 , excellent cycling stability after 36 000 cycles, and a steady electrochemical impedance behavior after 120 h of floating.