Effect of Doping Ions on Electrochemical Capacitance Properties of Polypyrrole Films

Conducting polypyrrole (PPy) films doped with p-toluenesulfonate (TOS−), ClO4−, and Cl− were electrochemically prepared, respectively. The electrochemical capacitance properties of the PPy films were investigated with cyclic voltammetry (CV), galvanostatical charge/discharge, and electrochemical impedance spectroscope (EIS) techniques. The morphology observation and structure analysis of PPy films were performed by scanning electron microscope (SEM) and X-ray diffraction (XRD). The results showed that PPy-Cl and PPy-TOS were characterized with a highly porous and ordered structure, which led to their fast ion switch processes. Moreover, they exhibited a rectangle-like shape of voltammetry characteristics even at a scanning rate of 50 mV·s−1, a linear variation of the voltage with respect to time in the charge/discharge process, and almost ideal capacitance behavior in low frequency, even in deeply charged/discharged states in 1 mol·L−1 KCl solution. Furthermore, specific capacitance of PPy-Cl (polymerization charge of 2 mAh·cm−2) could reach 270 F·g−1 (scanning rate of 5 mV·s−1) or 175 F·g−1 (scanning rate of 200 mV·s−1) and its specific energy could reach 35.3 mWh·g−1. Moreover, with heavier doping ion (TOS−), PPy-TOS (polymerization charge of 2 mAh·cm−2) had a slightly smaller specific capacitance (146 F·g−1, scanning rate of 5 mV·s−1), but a very rapidly charge/discharge ability (specific capacitance of 123.6 F·g−1 at scanning rate of 200 mV·s−1) and its specific power could reach 10 W·g−1. In addition, both PPy-TOS and PPy-Cl had good cycleability. All of the above implied that the PPy-Cl and PPy-TOS were two kinds of promising electrode material for supercapacitors.