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

• DOI: 10.1016/j.electacta.2012.10.106
• Publication Date: 2012-11-12T17:29:06Z
• Authors: Lingjuan Deng; Zhengping Hao; Jianfang Wang; Gang Zhu; Liping Kang; Zong-Huai Liu; Zupei Yang; Zenglin Wang
• Keywords: 02 engineering and technology; 0210 nano-technology; 7. Clean energy

Abstract Graphene/multiwall carbon nanotubes/MnO 2 (GR/MCNTs/MnO 2 ) 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 KMnO 4 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 MnO 2 with layered structure is 37% in the hybrid material. An asymmetrical electrochemical capacitor (EC) is assembled using GR/MCNT/MnO 2 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 Na 2 SO 4 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/MnO 2 (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.