Visible-Light-Sensitized Production of Hydrogen Using Perfluorosulfonate Polymer-Coated TiO₂ Nanoparticles:  An Alternative Approach to Sensitizer Anchoring

TiO₂ sensitized by derivatized ruthenium bipyridyl complexes has been intensively investigated as a tool to utilize visible light. This article describes an alternative approach to attaching ruthenium complex sensitizers at the TiO₂/H₂O interface, which is a much simpler and more efficient way to produce hydrogen. The surface of TiO₂ particles are simply coated with perfluorosulfonate polymer (cation-exchange resin:  Nafion), and then Ru(bpy)₃²⁺ (as a cationic form), whose bipyridyl ligands are not functionalized with carboxylic acid groups, are bound within the Nafion layer through electrostatic attraction. The visible-light-induced production of H₂ on Nf/TiO₂ using simple Ru(bpy)₃²⁺ as a sensitizer is far more efficient than that on Ru(dcbpy)₃−TiO₂, upon which many sensitized photoelectrochemical conversion systems are based. Effects of various experimental parameters such as pH, concentration of Ru(bpy)₃²⁺, Nafion loading, and the kind of TiO₂ were investigated. Under optimized conditions, the H₂ production rate was about 80 μmol/h, which corresponds to an apparent photonic efficiency of 2.6%. The roles of the Nafion layer on TiO₂ in the sensitized H₂ production are proposed to be twofold:  to provide binding sites for cationic sensitizers and to enhance the local activity of protons in the surface region.