Asymmetric supercapacitor, based on composite MnO2-graphene and N-doped activated carbon coated carbon nanotube electrodes

Manganese dioxide nanotubes and activated carbon coated multiwalled carbon nanotubes (AC-MWCNT) are prepared by hydrothermal methods. MnO2-graphene positive electrodes with good dispersion of individual components are fabricated using poly[1-[4-(3-carboxy-4-hydroxyphenylazo)benzenesulfonamido]-1,2-ethanediyl, sodium salt] (PAZO) as a co-dispersant. The unique structure of PAZO, containing chelating aromatic monomers allows for efficient adsorption of this polyelectrolyte on MnO2 and graphene, which is a prerequisite for their efficient electrosteric co-dispersion. The MnO2-graphene electrodes with active mass loading of 30mgcm−2 show a capacitance of 3.3Fcm−2 at a scan rate of 2mVs−1 and a capacitance retention of 64% is achieved with increase of scan rate from 2 to 100mVs−1. The use of AC-MWCNT with thick AC coating allows the fabrication of negative electrodes, which closely match the capacitive performance of the positive electrodes. The asymmetric supercapacitors containing MnO2-graphene positive electrodes and AC-MWCNT negative electrodes show capacitance of 1.42Fcm−2 at a scan rate of 2mVs−1, capacitance retention of 52% in the scan rate range of 2–100mVs−1 in a voltage window of 1.8V.