Thickness dependence of the constant phase element behavior of poly(o-toluidine) impedance response

M. J. RODRÍGUEZ PRESA; R. I. TUCCERI; M. I. FLORIT; D. POSADAS

Poraj

Workshop; NATO Advanced Research Workshop on Electrochemistry of Electroactive Polymer Films WEEPF-2000; 2000

International Society of Electrochemistry

Constant Phase Element (CPE) behaviour of blocking interfaces is characterized by an impedance of the type [1]: Z = RLF + Y0-1 (j )- (1) Where RLF is the low frequency resistance, Y0-1 is the constant phase parameter, j =  -1,  the circular frequency and  is a number comprised between 0.5 and unity.Recently the CPE behaviour has been employed to characterize the surface roughness of electrode surfaces [2]. On the other hand, the impedance response of polymers derived from arylamines and ring substituted aryl amines shows, at low frequencies, a CPE behaviour of the type represented by eq, (1) [3-5]. In this work it is reported the dependence of  on the polymer thickness and on the applied potential, E, for poly-o- toluidine (POT) in its conducting state. Here the thickness is expressed in terms of the anodic oxidation charge, Q, of the polymer film. The experimental conditions are the same as those reported elsewhere [4,5]. At E = 0.6 V vs. sce,  first increases with Q and then decreases . This is explained by an increase in the surface roughness of the polymer as the thickness increses. This is in agreement with previous STM and SEM experiments reported in the literature [4,6,7]. For a given thickness,  increases with the applied potential (Fig.2). This is explained by an increase in the effective diffusion coefficient as the potential is made more positive. References 1. A. Lasia, in Modern Aspects of Electrochemistry, Number 32, B.E.Conway et al., Kluwer Academic/Plenum Publishers, New York, 1999. 2. U. Rammel and G. Reinhard, Electrochim. Acta. 35 (1990) 1045. 3. M. M. Musiani, Electrochim. Acta, 35 (1990) 1665. 4. M. J. Rodríguez Presa, H. Bandey, R. I. Tucceri, M. I. Florit, A. R. Hillman and D. Posadas, Electrochim. Acta, 44 (1999) 2073. 5. M. I. Florit, D. Posadas, E. M. Andrade and F. V. Molina, J. Electrochem. Soc., 146 (1999) 2592. 6. T. L. Porter, Surf. Sci., 293 (1993) 81. 7. M. E. Vela, G. Andreasen, R. C. Salvarezza and A. J. Arvia, J. Chem. Soc., Faraday Trans., 92 (1996) 4093.