Molecular Cu(I)-Cu(II) Photosensitizer-Catalyst Photoelectrode for Water Oxidation

Photochemical splitting of H₂O to H₂ and O₂ is one approach to generate "solar fuels." Cu(II)-based electrocatalysts for water oxidation in aqueous solution have been studied previously, but photodriving these systems still remains a challenge. Light harvesting units can be employed for this purpose, that upon photoexcitation generate a high energy excited state and give rise to a charge separated state. In this work, a bis-diimine Cu(I)-based donor-chromophore-acceptor (D-C-A) system is synthesized, characterized, and applied as the light harvesting component of a photoanode. Here, this molecular assembly was integrated onto a zinc oxide (ZnO) nanowire surface on a fluorine-doped tin oxide (FTO) glass slide. Upon photoexcitation, chronoamperometric studies reveal that the integrated triad can inject electrons directly into the conduction band of zinc oxide generating oxidizing equivalents that are then transferred to a Cu(II) water oxidation catalyst in aqueous solution yielding O₂ from H₂O with a Faradaic efficiency of 76%.