Fabrication and supercapacitive behavior of tetramethylammonium ion-intercalated MnO2 prepared by an exfoliation and self-assembly process

• TMA+ intercalated MnO2 was synthesized via an exfoliation and self-assembly process.
• The as-prepared self-assembled MnO2 exhibits an ordered layered structure.
• The as-prepared MnO2 possesses a large interlayer spacing of 0.67 nm.
• The maximum specific capacitance of self-assembled MnO2 is 180 F g−1 at 0.5 A g−1.
• The specific capacitance of self-assembled MnO2 decreased 10% after 10,000 cycles.

Layered birnessite-type manganese oxide is exfoliated into single-layer manganese oxide nanosheets. Then, the exfoliated manganese oxide nanosheets are spontaneously restacked by a self-assembly process, which is driven mainly by electrostatic interactions between the negatively charged manganese oxide nanosheets and the positively charged tetramethylammonium (TMA+) ions, yielding a new ordered layered structure of MnO2 (self-assembled MnO2) with a large interlayer spacing of 0.67 nm, suggesting the formation of a layered hybrid form, intercalated with TMA+ ions in residence between the manganese oxide nanosheets. The large interlayer spacing facilitates rapid ion exchange and the intercalation and deintercalation of electrolyte cations. The supercapacitive behavior of the as-prepared self-assembled MnO2 is evaluated by cyclic voltammetry (CV), galvanostatic charge–discharge (CD) experiments and electrochemical impedance spectroscopy (EIS). The specific capacitance value is 180 F g−1 at a current density of 0.5 A g−1. After 10,000 cycles, the specific capacitance is still approximately 90% of the maximum specific capacitance. In addition, the intercalation of TMA+ ions between the manganese oxide nanosheets leads to a low charge-transfer resistance. These experimental results demonstrate that this self-assembled MnO2 is a promising candidate for use as electrode material in supercapacitor applications.