REVERSIBLE VOLTAMMETRIC RESPONSE OF ELECTRODES COATED WITH PERMSELECTIVE REDOX FILMS

Experimental and calculated cyclic voltammograms are compared for elec trodes modified with thin films of permselective ion exchangers in whi ch the exchange sites are covalently attached redox sites. The voltamm ograms are considered in the thin-layer limit in which mass transfer d oes not limit the current response. Additionally, it is assumed that n either the rate of heterogeneous electron transfer at the electrode-fi lm interface nor the rate of homogeneous electron transfer in the bulk of the film limit the current. Under these circumstances, changes in the charge on the polymer backbone change the Donnan potential at the film-solution interface to produce broadened, asymmetrical voltammogra ms. Shifts in the apparent formal potentials for permselective redox f ilms are also predicted if the activity of the counterion in the bathi ng electrolyte solution changes. Good agreement between the permselect ive model and experiment is obtained for the shape of the voltammogram s. Once changing liquid junction potentials and changing activity coef ficients in solution taken into account, good agreement is also obtain ed for the shifts in the apparent formal potentials.