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

Abstract

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.