ELECTRON AND COUNTERION DIFFUSION CONSTANTS IN MIXED-VALENT POLYMERICOSMIUM BIPYRIDINE FILMS

Recent theory has shown that, in transient electrochemical oxidation o r reduction of a redox polymer film, electroneutrality coupling betwee n concurrently transported electrons and counterions in the polymer fi lm can enhance the rate of electron-hopping transport as expressed by the apparent electron diffusion coefficient D-e,D-app. We have investi gated this problem in the redox polymers poly '-bipyridine)(2)(N-(4-py ridyl)cinnamamide)(2)](2+) (poly-I), -bipyridine)(2)(4-vinylpyridine)( 2)](2+)(poly-II), and 4-vinyl-4'-methyl-2,2'-bipyridine)3](2+)(poly-II I) by measuring and comparing the diffusion coefficients (D-cl) of Cl- counterions in the cationic polymer Alms to the transient chronoamper ometric (D-e,D-app) and steady-state (D-e) electron diffusion coeffici ents. At room temperature, the ratio sigma=D-ion/D-e is 1.25, 0.16, an d 0.076 for the three redox polymers, respectively. According to the e lectroneutrality coupling theory, the coupling effect is insignificant in poly-I films at room temperature, with and without dilution of the Os centers by copolymerized Ru complexes, but at lowered temperature, assuming sigma-->0, coupling in poly-I has a substantial effect. Elec troneutrality coupling in poly-III films enhances the room temperature chronoamperometric D-e,D-app over the (''true'') steady-state'D-e val ue by ca.2-fold. The lack of agreement between experiment and bimolecu lar electron self-exchange for microscopic (bounded) diffusion of Os s ites, as reflected in an Os site concentration-dependent activation ba rrier for D-e,D-app.