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

Layer-by-Layer\n(LbL) polyelectrolyte self-assembly occurs by the\nalternate exposure of a substrate to solutions of oppositely charged\npolyelectrolytes or polyions. Here, we report the application of LbL\nto construct chromophore–catalyst assemblies consisting of\na cationic polystyrene-based Ru polychromophore (PS-Ru) and a [Ru­(tpy)­(2-pyridyl-N-methyl­benzimidazole) (OH₂)]²⁺ water oxidation catalyst (RuC), codeposited with poly­(acrylic acid)\n(PAA) as an inert polyanion. These assemblies are deposited onto planar\nindium tin oxide (ITO, Sn:In₂O₃) substrates\nfor electrochemical characterization and onto mesoporous substrates\nconsisting of a SnO₂/TiO₂ core/shell structure\natop fluorine doped tin oxide (FTO) for application to light-driven\nwater oxidation in a dye-sensitized photoelectrosynthesis cell. Cyclic\nvoltammetry and ultraviolet–visible absorption spectroscopy\nreveal that multilayer deposition progressively increases the film\nthickness on ITO glass substrates. Under an applied bias, photocurrent\nmeasurements of the (PAA/PS-Ru)₅/(PAA/RuC)₅ LbL\nfilms formed on FTO//SnO₂/TiO₂ mesoporous core–shell\nelectrodes demonstrate a clear anodic photocurrent response. Prolonged\nphotoelectrolysis experiments, with the use of a dual working electrode\ncollector–generator cell, reveal production of O₂ from the illuminated photoanode with a Faradaic efficiency of 22%.\nThis is the first report to demonstrate the use of polyelectrolyte\nLbL to construct chromophore–catalyst assemblies for water\noxidation.