HETEROGENEOUS ELECTRON-TRANSFER AT ELECTRODES COATED WITH ELECTRONICALLY CONDUCTING NICKEL-TETRAAMINOPHTHALOCYANINE POLYMER-FILMS

The kinetics of heterogeneous electron transfer across films of electr onically conducting nickel-4,4',4'',4'''-tetraaminophthalocyanine poly mer (poly(NiTAPc)) are reported. Poly(NiTAPc), which is formed by oxid ative electropolymerization of NiTAPc, acts as an n-doped electronic c onductor between about 0.8 and - 2.0 V vs. Ag/AgCl. Within this range it sustains diffusion-limited charge transfer to one-electron bulk sol ution reactants at their anticipated formal potentials. However, the r ates of heterogeneous electron transfer to these species are diminishe d by a small, uniform amount that is exponentially dependent on film t hickness. Results are interpreted in terms of a porous electrode model in which electron transfer occurs at the polymer-solution interface, a large bulk capacitance arises from an interior pore volume that is i naccessible to diffusing reactants and a resistive element (suggested to be pores of electrolyte trapped between aggregrates of the polymer) is present which acts to reduce apparent values of k(s,h). It is demo nstrated that electronically conducting polymer films do not accelerat e the rate of electron transfer to solution reactants but rather resto re kinetics to their anticipated values by preventing suface involveme nt.