Pergaman Ekcmchtmica Acta, Vol. 40. No. 8. pp. 1037-1040, 1995 Copyright 0 1995 l?lscvia Bcicma Ltd. Printed in Great Britain. AU ri&tt# tucrwd 0013~4686/9s 59.50 + 0.00 zyxwvut IMPEDANCE CHARACTERISTICS OF POLY-O- AMINOPHENOL ELECTRODES C. BARBERO,*~ R. I. TUCCFZRI,~ D. POSADAS,~!~ J. J. SILBER~ and L. SERENO~ t lnstituto de Investigaciones Fisicoquimicas Tebricas y Aplicadas (INIFTA), Fact&ad de Ciencias Exactas, Universidad National de La Plata, Sucursal 4, Casilla de Correo 16, 1900, La Plata, Argentina 1 Universidad National de Rio Cuarto, Departamento de Quimica y Fisica, Estafeta Postal No. 9, 5800, Rio Cuarto, Argentina (Received 6 zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCB April 1994) Akatraet-The impedance characteristics of poly-e-aminophenol film electrodes in NaClO, 0.4M + HCIO, 0.1 M electrolyte have been measured in the frequency range 0.01 c f < 10” Hz and at two different thicknesses. The experimental results can be interpreted through a simple charge transfer resist- ance in parallel with a constant, capacity at high frequencies and the redox capacity in series with the fdm resistance at low frequencies. The analysis of the impedance response allows to the electrochemical rate constant, the concentration of redox centers in the film, the film conductivity and the diffusion coelIicient of the elections to be determined. Key words : impedance, poly-o-aminophenol, modified electrodes. 1. INTRODUCTION In previous work we have studied the electrochemical[ 11 and optical[2] properties of poly-o-aminophenol (POAP). Electrochemical impedance spectroscopy (EIS) has proven to be a valuable technique for determining important char- acteristics of electrochemically active polymers (see Ref. 3 for a review). Since POAP differs both in the electrochemical response as well as in structure from the more investigated polyaniline (PANI) it seems interesting to study the first by EIS in order to deter- mine its characteristic electrochemical parameters. 2. EXPERIMENTAL o-Aminophenol (Fluka) was purified as described previously[l]. Water was obtained from a Mini-Q (Millipore). NaClO, and HClO, (Merck, ar grade) were used without further purification. The poly-o-aminophenol (POAP) modified elec- trodes were prepared as previously reported[2]. Two different film thickness, zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA d, were used: 30 and 300 nm. The films were grown to the approximate desire thickness by using the reduction charge vs. ellip- sometric thickness working curve reported elsewhere[2]. The base working electrode was a Platinum wire (0.52 cm long, o.d. 0.05 cm). A large area Pt counter electrode was employed. The reference electrode was * Present address: Paul Scherrer Institut, Wtirlinggen und Villigen, CH-5232, Villigen, Switzerland. $ Author to whom correspondence should be addressed. a hydrogen electrode. The electrolytic solution was 0.1 M HClO, + 0.4 M NaClO, . Impedance measurements at constant applied potential were carried out with a Solartron Model 1286 Potentiostat and a Solartron Model 1250 Fre- quency Response Analyzer. Data were acquired at seven discrete frequencies, j, per decade in the range 0.01 Hz <f< 10kHz. An amplitude of 5 x 10-j V (rms) was employed. 3. RESULTS AND DISCUSSION The voltammetric response of the POAP film is shown in Fig. 1 for d = 30nm. The voltammogram shows the characteristic response of a reversible redox film as discussed elsewere[l, 21. It should be emphasized here the appearance of only one voltam- metric peak for POAP as opposed to the two main peaks in PANIC41 and poly-o- toluidine (POT)[5]. -80 - I I I I I I I c -0.1 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 E I V (nhe) Fig. 1. Voltammetric response of POAP, v = 0.034 V s- 1037 Et? bO:l-H