The effect of temperature on the impedance of poly-o-toluidine in 3.7 M H2SO4

The impedance response of poly(o-toluidine) (POT) electrochemically grown f ilms was investigated in sulfuric acid 3.7 M, in the temperature range 218 to 293 K. The Nyquist diagrams as a function of temperature show that the t ransition potential from the nonconductive to the conductive state shifts i n the positive potential direction as the temperature decreases. This impli es that, at low temperatures, a greater field is needed to induce the trans ition. In the nonconductive state both the high-frequency and the low-frequ ency resistances increase as the temperature is decreased. The Arrhenius pl ots for both show a break at about 255 K. This is in agreement with the fac t that the high-frequency resistance is controlled by ionic movements and t hat there is charge-transfer control at the polymer/solution interface. In the conductive state the low-frequency capacitance is independent of temper ature, showing that the active site concentration does not depend on the te mperature. The low-frequency resistance in this potential region also depen ds on the temperature. No break is observed in the Arrhenius plot for this quantity. However from its slope it is inferred that ionic motions within t he polymer control the charge transport in this state. (C) 1999 The Electro chemical Society. S0013-4651(98)10-051-4. All rights reserved.