Direct synthesis of porous carbon nanotubes and its performance as conducting material of supercapacitor electrode

Porous carbon nanotubes (CNTs) were directly synthesized for the first time by arc discharge in the presence of CO2. Supercapacitor was fabricated with the addition of CNTs synthesized in different medium to the polarizable activated carbon (AC) electrode as conducting material for comparison purpose. The electrical properties of the AC/CNTs composite are systematically investigated using cyclic voltammetric, discharge at constant current and electrochemical impedance spectroscopic (EIS) techniques. Transmission electron microscope (TEM) observation reveals that a few CNTs synthesized in the presence of CO2 are porous ones. Specific capacitance (Csp) of the AC/CNTs composite passes through a maximum with increasing discharge current while the average internal resistance (Ri) of supercapacitor decreases with increasing discharge current. The Csp of AC/CNTsHe/C2H2/CO2 composite with CNTs synthesized in He, C2H2 and CO2 medium is bigger than that of AC/CNTsN2/C2H2/CO2 or AC/CNTsN2/C2H2 composite. The Ri of AC/CNTsHe/C2H2/CO2 composite is the same as that of AC/CNTsN2/C2H2 composite, which is smaller than that of AC/CNTsN2/C2H2/CO2 composite. EIS results show that the AC/CNTs composite have the similar charge storage mechanism. The above results show that CNTsHe/C2H2/CO2 is one of the suitable conducting materials to decrease the resistance of supercapacitor while maintaining its higher specific capacitance.