Stable Molecular Photocathode for Solar-Driven CO₂ Reduction in Aqueous Solutions

The performance of dye-sensitized photoelectrodes for artificial photosynthesis is typically limited by instability in aqueous solutions. We describe here a new molecular-based photocathode that integrates functional chromophore–catalyst assemblies for long-term solar-driven CO2 reduction in stabilized polymeric film structures. The assemblies include a silane surface-anchoring bridge, a ruthenium polypyridyl chromophore, and a rhenium-based molecular catalyst. They were prepared on nanocrystalline oxide films by silanization of the oxide and two-step electropolymerization of vinyl-derivatized precursors. The integrated photocathode was stable toward CO2 reduction for over 10 h with a Faradaic efficiency of ∼65%. The long-term stability arises from the silane surface-anchoring groups and the carbon–carbon bonds formed by electropolymerization between the three components. Transient absorption measurements on a nano-to-microsecond time scale show that the assemblies undergo rapid hole injection into the oxide electrode followed by relatively slow interfacial charge recombination.