Charge transfer between polyaniline and carbon nanotubes supercapacitors: Improving both energy and power densities

The charge transfer properties of a novel asymmetric device configuration combining polyaniline (PANI) as the battery component and single-wall carbon nanotubes (SWNTs) as the supercapacitor component were investigated. The scan rate in cyclic voltammetry is an important factor modulating the relative weight of the fast double layer/pseudocapacitance and slow electrochemical capacitance and changing the total charge and energy density output. At a scan rate of 1 mV/s, the energy density of the PANI-SWNTs device is six times higher than that of the bare SWNTs device. At different voltage ranges of galvanostatic discharge, the PANI-SWNTs device exhibits three different discharge behaviors. The SWNT-like discharge dominates the initial stage. The PANI electrochemical reaction dominates the middle stage of the discharge, which coincides with the PANIs conductive state. Once the charge from the PANI electrochemical reaction is used up, the remaining charge in SWNTs sustains the discharge in the final stage. A suspension period was therefore introduced to the middle stage of PANI-SWNTs device discharge, which resulted in a 10% increase of the power density. The understanding of the interaction between the fast double layer/pseudocapacitance and slow electrochemical capacitance benefits for designing the architecture of supercapacitor-battery satisfying energy and power requirements of practical applications.