Water oxidation by a noble metal-free photoanode modified with an organic dye and a molecular cobalt catalyst

Abstract

A low-cost and easy-to-construct dye-sensitized photoanode for water oxidation was prepared by co-loading a new triphenylamine donor–acceptor organic chromophore (D1) and a Co₄O₄ cobalt cubane-based water oxidation catalyst (CoF) on TiO₂ thin films. As the first example of a molecular catalyst-based, noble metal-free, dye-sensitized photoanode, the electrode, TiO₂|D1,CoF, produces a higher photocurrent than other noble metal-free, dye-sensitized photoanodes with a relatively high faradaic efficiency for O₂ production. The success of the dyad system lies in retarded interfacial charge recombination and extended light absorption both of which take advantage of the pyridine anchor-functionalized chromophore. In addition, the CoF catalyst, decorated with hydrophobic aliphatic chains, serves as a protective layer for stabilizing the organic dyes on electrode surfaces. Transient absorption measurement suggests the accumulation of oxidative equivalents on CoF by electron transfer on the TiO₂ surface. The results and design principles presented here demonstrate the use of molecular engineering as a powerful tool for the exploration of low-cost solar water-splitting devices.