Photocathode Chromophore–Catalyst Assembly via Layer-By-Layer Deposition of a Low Band-Gap Isoindigo Conjugated Polyelectrolyte

Low band-gap conjugated polyelectrolytes (CPEs) can serve as efficient chromophores for use on photoelectrodes for dye-sensitized photoelectrochemical cells. Herein is reported a novel CPE based on poly­(isoindigo-<i>co</i>-thiophene) with pendant sodium butylsulfonate groups (PiIT) and its use in construction of layer-by-layer (LbL) chromophore–catalyst assemblies with a Pt-based H⁺ reduction catalyst (PAA-Pt) for water reduction. A novel Stille polymerization/postpolymerization ion-exchange strategy was used to convert an organic-soluble CPE to the water-soluble poly­(isoindigo-<i>co</i>-thiophene). The anionic PiIT polyelectrolyte- and polyacrylate-stabilized Pt-nanoparticles (PAA-Pt) were codeposited with cationic poly­(diallyldimethylammonium) chloride (PDDA) onto inverse opal (IO), nanostructured indium tin oxide film (nITO) (IO nITO) atop fluorine doped tin oxide (FTO), by using LbL self-assembly. To evaluate the performance of novel conjugated PiIT//PAA-Pt chromphore–catalyst assemblies, interassembly hole transfer was investigated by photocurrent density measurements on FTO//IO nITO electrodes. Enhanced cathodic photocurrent is observed for the polychromophore–catalyst assemblies, compared to electrodes modified with only PiIT, pointing toward photoinduced hole transfer from the excited PilT to the IO nITO. Prolonged photoelectrolysis experiments reveal H₂ production with a Faradaic yield of approximately 45%. This work provides new routes to carry out visible-light-driven water reduction using photocathode assemblies based on low band-gap CPEs