Photoanodes for water oxidation with visible light based on a pentacyclic quinoid organic dye enabling proton-coupled electron transfer

A pentacyclic quinoid dye, KuQ(O)3OH, combining (i) extended visible absorption up to 600 nm, (ii) excited state reduction potential > 2 V vs NHE, (iii) photoinduced proton coupled electron transfer mechanism, has been used for the fabrication of dye-sensitized SnO2 photoanodes integrating a ruthenium polyoxometalate water oxidation catalyst. The resulting photoelectrodes SnO2|KuQ(O)3OH|Ru4POM display a Light Harvesting Efficiency up to 90% in the range 500 – 600 nm, onset potential as low as of 0.2 V vs NHE at pH 5.8, photoinduced oxygen evolution with faradaic efficiency 70±15% and absorbed-photon-to-current efficiency up to 0.12±0.01%.