Preparation and capacitance of graphene/multiwall carbon nanotubes/MnO2 hybrid material for high-performance asymmetrical electrochemical capacitor

Graphene/multiwall carbon nanotubes/MnO2 (GR/MCNTs/MnO2) hybrid material with a specific capacitance of 126 F g−1 within a potential window of 0–1.1 V vs. saturated calomel electrode has been synthesized by a simple redox reaction between graphene/multiwall carbon nanotubes (GR/MCNTs) and KMnO4 at room temperature. The morphology and structure of the obtained material are examined by XRD, SEM and TEM. The electrochemical properties are characterized by cyclic voltammetry, galvanostatic charge–discharge and electrochemical impedance spectroscopy. The mass percentage of MnO2 with layered structure is 37% in the hybrid material. An asymmetrical electrochemical capacitor (EC) is assembled using GR/MCNT/MnO2 hybrid material as positive electrode and GR/MCNT material as negative electrode, respectively. The electrochemical properties of the two electrodes and the asymmetrical EC are investigated in 1 mol L−1 Na2SO4 aqueous electrolyte. The asymmetrical EC can cycle reversibly in a cell potential of 0–2.0 V and gives a high energy density of 28.33 Wh kg−1, which is much higher than those of symmetrical ECs based on GR/MCNT/MnO2 (6.20 Wh kg−1) and GR/MCNT (3.92 Wh kg−1). Moreover, the asymmetrical EC presents a high power density (5 kW kg−1 at 13.33 Wh kg−1) and excellent cycling performance of 83% retention after 2500 cycles.

An asymmetrical electrochemical capacitor (graphene/MCNT/MnO2//graphene/MCNT) has been assembled using aqueous Na2SO4 solution as electrolyte. The asymmetrical electrochemical capacitor with high energy density can cycle reversibly in a cell potential of 0–2.0 V and gives excellent cycling performance.Figure optionsDownload as PowerPoint slideHighlights
► GR/MCNT/MnO2 hybrid material within a potential window of 0–1.1 V vs. SCE has been prepared.
► An asymmetric electrochemical capacitor working at 2.0 V in aqueous medium is assembled based on the GR/MCNT/MnO2 and GR/MCNT.
► The asymmetric electrochemical capacitor exhibits high energy density and excellent cycle performance.