Macrokinetics of polyaniline based electrode: effects of porous structure,microkinetics, diffusion, and electrical double layer

The standard porosimetry method (SPM) was used to study in situ real porous structures of poly(aniline) (PAn) swollen in electrolytes containing gamma -butyrolactone (GBL). The effects of swelling, the degree of doping, the na ture of counterions, and type the of polymerization (chemical or electroche mical) on porous PAn structure were studied. All the PAn forms impregnated with GEL had high porosities of several dozen per cent, high specific surfa ce areas of 80-400 m(2) cm (-3), pore radii of 1-100 nm, and average fibril radii of 2-10 nm. Electrochemically synthesized PAn showed better electroc hemical characteristics than chemically synthesized PAn. The model of the i ntercalated porous electrode was used to characterize the discharge curves. Comparison of calculated and experimental curves enabled determination of essential microscopic characteristics: specific exchange current density (i (0)) of real PAn/electrolyte interphase doping-dedoping, specific capacity (C-S) of electrical double layer (EDL) of this interface, and diffusion coe fficient (D) of counterions in the polymer. These characteristics depend up on the nature of counterions and the method of polymerization (chemical or electrochemical). Small D values of 8 x 10(-19)-1 x 10(-17) cm(2) s (-1) re sult from the solid-phase nature of diffusion; i(0) = 1 x 10(-15)-1 x 10(-1 2) A cm (-2), and C(s=)0.6-5.0 mu F cm(-2). Very low D, i(0) and C-S are co mpensated by very high S resulting in better electrochemical characteristic s. Thin electrodes (< 1 mm) showed very small ohmic losses, while the rate of electrochemical doping-dedoping was usually limited by solid-phase diffu sion and discharge. The effects of structure, mode, and microscopic paramet ers on discharge curves were analyzed. (C) 1999 Elsevier Science Ltd. All r ights reserved.