Journal of Electroanalytical Chemistry, 368 (1994) 23-31 23 Mechanism of ionic and redox sensitivity of p-type conducting Part 1. Theory Andrzej Lewenstam l polymers Laboratory of Analytical Chemhtry, A&o Akademi University, SF-20500 Turku- A’bo (Finland) and Faculty of M aterial Science and Ceramics, University of Mining and Metallurgy, 30-059 Cracow (Poland) Johan Bobacka and Ari Ivaska Laboratory of Analytical Chemistry, A’bo Akademi University, SF-20500 Turk&b0 (Finland) (Received 6 January 1993, in revised form 12 July 1993) zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA Abstract Equations have been derived to describe the open-circuit potentiometric response of a p-type conducting polymer membrane. The final model is derived step by step from the model of a single-metal electrode by using the concept of solvated electron and from the model of a solid-state ion-selective and/or electron-selective electrode containing a sparingly soluble metal-rich salt in the membrane. Ah electrodes considered, i.e. the metal, ion-selective and polymer electrodes, are presented as systems based on an ionic salt of the M+e- type. The ionic and redox sensitivities of a p-type conducting polymer are described by assuming two possible equilibration pathways. In the first approach the ion-electron exchange process at the polymer surface without a change of the oxidation state of the polymer is discussed and in the second the metathesis of the polymer surface with a concurrent change in the oxidation state of the polymer is considered. The equations derived allow us to interpret the anionic, cationic and redox sensitivities and to discuss the observed changes in the standard potentials. 1. Introduction The theory presented and the equations derived in this paper are based on the fundamental concept of the equilibrium between a metal and a solvent devel- oped in the 1970s by the groups of Frumkin and Trasatti [1,2]. An electric potential drop (Galvani po- tential difference, inner potential difference (pd)) be- tween two immiscible phases, which are thick in com- parison with the width of the double layer, and con- taining mobile charges will be discussed. A fundamen- tal equation describing the cationic, anionic and redox sensitivities of a p-type conducting polymer (CP> will be derived step by step. All equations will be framed in the terms of the electrochemical potential of ions and l To whom correspondence should be addressed at Abe Akademi University. 0022-0728/94/$7.00 SSDIOO22-0728(93)03080-9 the electron. The following assumptions will be used throughout [3]. (i) The only driving forces in the systems studied are the differences in concentrations and inner electric potentials. (ii) Concentration and concomitant potential gradi- ents extend only in a direction perpendicular to the flat macrosurface of the electroactive part of the electrode (disc, pellet, membrane, or film). (iii) Charge transfer and ion-electron exchange pro- cesses between the electrode and solution are fast and reversible; fast reversible ion/electron-binding pro- cesses in the electroactive phase of the electrode and solution are permitted. (iv) Bulk concentrations of species in the different phases are equal to their surface concentrations. (v) Adsorption and contamination processes are ne- glected. 0 1994 - Elsevier Sequoia. All rights reserved