The measurement of specific capacitances of conducting polymers using the quartz crystal microbalance

Mass specific capacitance (F g−1) of conducting polymers is an important factor in selecting these materials for use in supercapacitors. Presented in this work is a new method for measuring the mass specific capacitance of conducting polymers using the electrochemical quartz crystal microbalance (EQCM). It can be done by one of two ways: (1) using one thin deposit, calculating the capacitance and dividing by the deposition mass, or (2) conversion of the capacitance per deposition charge (for thick deposits) to capacitance per mass using Faraday’s Law and the EQCM data (for thin deposits). Using the new method, specific capacitances of polyaniline, polypyrrole and poly[3,4-ethylenedioxythiopene] comparable to those quoted in the literature are found. Such obtained mass specific capacitance should effectively be the theoretical maximum capacitance that can be extracted from a thick film. The standard plots of mass vs. potential were converted to “massograms” by differentiating the mass with respect to time. As the mass variation rate, dM/dt, is proportional to the current, I, the plot is directly comparable to the voltammogram. The onset of polymerisation and nucleation loops are made more apparent using the massogram plot. Using this data, the ideal deposition potentials for the conducting polymers can be determined.