Light-Driven Water Oxidation Using Polyelectrolyte Layer-by-Layer Chromophore–Catalyst Assemblies

Layer-by-Layer (LbL) polyelectrolyte self-assembly occurs by the alternate exposure of a substrate to solutions of oppositely charged polyelectrolytes or polyions. Here, we report the application of LbL to construct chromophore–catalyst assemblies consisting of a cationic polystyrene-based Ru polychromophore (PS-Ru) and a [Ru­(tpy)­(2-pyridyl-<i>N</i>-methyl­benzimidazole) (OH₂)]²⁺ water oxidation catalyst (RuC), codeposited with poly­(acrylic acid) (PAA) as an inert polyanion. These assemblies are deposited onto planar indium tin oxide (ITO, Sn:In₂O₃) substrates for electrochemical characterization and onto mesoporous substrates consisting of a SnO₂/TiO₂ core/shell structure atop fluorine doped tin oxide (FTO) for application to light-driven water oxidation in a dye-sensitized photoelectrosynthesis cell. Cyclic voltammetry and ultraviolet–visible absorption spectroscopy reveal that multilayer deposition progressively increases the film thickness on ITO glass substrates. Under an applied bias, photocurrent measurements of the (PAA/PS-Ru)₅/(PAA/RuC)₅ LbL films formed on FTO//SnO₂/TiO₂ mesoporous core–shell electrodes demonstrate a clear anodic photocurrent response. Prolonged photoelectrolysis experiments, with the use of a dual working electrode collector–generator cell, reveal production of O₂ from the illuminated photoanode with a Faradaic efficiency of 22%. This is the first report to demonstrate the use of polyelectrolyte LbL to construct chromophore–catalyst assemblies for water oxidation