Photoactive component-loaded Nafion film as a platform of hydrogen generation: Alternative utilization of a classical sensitizing system

The photochemical hydrogen production was achieved by integrating photoactive components in a polymer membrane film under visible-light irradiation. The classical homogeneous photochemical system employing ruthenium bipyridyl complex (Ru(bpy)32+) as a sensitizer, methyl viologen (MV2+) as an electron shuttle, Pt as a hydrogen-evolving catalyst was heterogenized by immobilizing the active components within Nafion film. The integrated Nafion film provides a unique environment in which the immobilization of the components, light absorption, charge separation/transfer, and hydrogen production concur. The hydrogen evolution from the loaded Nafion film under visible light (λ > 420 nm) was successfully demonstrated. The loaded Pt particles were mainly located at the external surface of the film while the sensitizer was bound at the cation-exchange sites in the nanoporous channel. The electron-relaying action of MV2+ was effective only above 1 mM because most MV2+ ions below this concentration were bound at the ion-exchange site with restricted mobility. The effects of various components on the hydrogen production in this heterogenized system were investigated and discussed. The present Nafion film system may serve as a prototype of solar hydrogen generating films and can be further modified and optimized for practical applications.