Effect of doping ions on electrochemical capacitance properties of polypyrrole films

Conducting polypyrrole films (PPy) 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), galvanostatic 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 charge/discharge process and almost ideal capacitance behavior in low frequency even on deeply charged/ discharged states in 1 mol . L-1 KCl solution. Furthermore, specific capacitance of PPy-Cl (polymerization charge of 2 mAh . cm(-2)) would 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 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 a good cycleability. All of the above implied that the PPy-Cl and PPy-TOS were two kinds of promising electrode material for supercapacitors.