Electron Transfer in the Reduction of Cobalt Porphyrin Incorporated into Nafion and Poly(4-vinylpyridine-co-styrene) Films

Mechanism of charge transport by redox metal complexes confined in polymer matrices

The mechanism of charge transport by metal complexes confined in polymer matrices is reviewed. There are two possibilities, one where the charge propagates in the matrix by diffusion of redox center molecules, and the other where the charge propagates by hopping between redox center molecules. The mechanism can be decided by investigating the dependence of the charge propagation rate on the redox center concentration, since in the diffusion mechanism the rate is first-order with respect to the concentration, while in the hopping mechanism it is second-order. In the hopping mechanism the charge-hopping distance can be analyzed by assuming a random distribution of the redox center in the matrix. The mechanism of charge transport by typical redox centers such as metal porphyrins, metal phthalocyanines, [Formula: see text] and methylviologen confined in a polymer membrane is presented and the charge-hopping distance is determined.

Electrocatalytic proton reduction by zinc phthalocyanine in nafion and poly(4-vinylpyridine-co-styrene) matrices

Electrochemical proton reduction was catalysed by zinc phthalocyanine ( ZnPc ) incorporated in a Nafion or poly(4-vinylpyridine-co-styrene) (P(VP-St)) film coated on a graphite electrode. The turnover number (TN) of the complex to catalyse H 2 evolution was 104 h-1. The TN of Nafion[ ZnPc ] was about two times higher than that of P(VP-St)[ ZnPc ]. The difference was ascribed to the electron propagation in the film influenced by the interaction of the complex with the matrix and by the counterion migration between the matrix and the electrolyte solution. The electron transfer in the reduction of the ZnPc complex in the matrix was concluded to be the rate-determining step for the proton reduction. The TN was independent of the ZnPc concentration in the matrix at low concentrations although H 2 formation was regarded to be a bimolecular reaction process, which was explained by the electron transfer through the matrix via a monomolecular diffusion which was the rate-determining step.