Asymmetric Supercapacitors Based on Activated‐Carbon‐Coated Carbon Nanotubes

Abstract

A new method is developed for the fabrication of asymmetric supercapacitor devices containing fibrous electrode materials. The approach is based on the synthesis of uniform polypyrrole (PPy) coatings on multiwalled carbon nanotubes (MWCNT), which were used for the fabrication of MWCNTs coated with N‐doped activated carbon (N‐AC). The N‐AC‐MWCNT electrodes show good electrochemical performance in positive and negative potential windows. The electrochemical performance of positive electrodes is further enhanced by the development of MnO2‐coated N‐AC‐MWCNT. In this approach, the problem of MWCNT degradation in the reaction with KMnO4 is avoided by the use of a sacrificial N‐AC layer, which allows a relatively high mass content of MnO2 in the final material. The approach offers the advantages of small size of MnO2 nanoparticles, good electrical contact of MnO2 and MWCNT and fibrous microstructure of the material. Testing results show a remarkably high specific capacitance of 6.29 F cm−2 (311.7 F g−1) at a mass loading of 20 mg cm−2. The important finding is the possibility to fabricate asymmetric devices, which show a specific capacitance of 2.19 F cm−2 (62.7 F g−1) in a voltage window of 1.9 V in aqueous Na2SO4 electrolyte, an energy density of 26.4 mWh g−1 and a power density of 1.7 W g−1. The electrodes and devices show good capacitance retention at high charge–discharge rates and good cycling stability. The asymmetric capacitors developed herein are promising for practical energy‐storage applications.

The Development of Pseudocapacitor Electrodes and Devices with High Active Mass Loading

“…The MnO 2 –graphene electrodes with active mass loading of 30 mg cm −2 showed [ 69 ] a capacitance of 3.3 F cm −2 at a scan rate of 2 mV s −1 , and a capacitance retention of 64% was achieved with the increase of scan rate from 2 to 100 mV s −1 . Another new development was the fabrication of MnO 2 ‐activated carbon coated carbon nanotube composites, [ 71 ] which showed a remarkably high specific capacitance of 6.29 F cm −2 (311.7 F g −1 ) at a mass loading of 20 mg cm −2 . The approach was based on the use of oxidant–surfactant nanocrystals, prepared by a chemical reaction between cetrimonium bromide and (NH 4 ) 2 S 2 O 8 .…”

Nitrogen-doped graphene–TiOxNy nanocomposite electrode for highly efficient capacitive deionization

“…6 Currently, most reported and commercialized CDI electrode materials are based on various kinds of novel porous carbon electrodes. [7][8][9][10][11][12][13][14] Graphene, as a novel two-dimensional carbon nanomaterial, has been widely used as the electrode materials in batteries and supercapacitors due to its high electrochemical performance and large surface area. [15][16][17][18][19][20] Its heteroatom-doped derivative, especially nitrogen-doped graphene (NG), has also been investigated as electrode materials to achieve even better electrochemical performance in batteries and supercapacitors as opposed to graphene due to nitrogen-doped active sites and enhanced electrical conductivity.…”

Facile and Sustainable Synthesis of Co3O4@Hollow-Carbon-Fiber for a Binder-Free Supercapacitor Electrode

“…Asymmetric supercapacitors are made up of a battery‐type electrode and a capacitor‐type electrode . Compared to conventional supercapacitors, asymmetric supercapacitors can make full use of potential windows of two electrodes to increase the operation voltage, which results in higher energy and power density . Up to now, various pseudocapacitive materials have been employed as positive electrode for asymmetric supercapacitors, such as conducting polymers and transition metal oxides/hydroxides .…”