Water Photo-oxidation Initiated by Surface-Bound Organic Chromophores

Abstract

Organic chromophores can be synthesized by established methods and offer an opportunity to expand overall solar spectrum utilization for dye-sensitized photoelectrosynthesis cells. However, there are complications in the use of organic chromophores arising from the instability of their oxidized forms, the inability of their oxidized forms to activate a water oxidation catalyst, or the absence of a sufficiently reducing excited state for electron injection into appropriate semiconductors. Three new triarylamine donor-acceptor organic dyes have been investigated here for visible-light-driven water oxidation. They offer highly oxidizing potentials (>1 V vs NHE in aqueous solution) that are sufficient to drive a water oxidation catalyst and excited-state potentials (∼-1.2 V vs NHE) sufficient to inject into TiO. The oxidized form of one of the chromophores is sufficiently stable to exhibit reversible electrochemistry in aqueous solution. The chromophores also have favorable photophysics. Visible-light-driven oxygen production by an organic chromophore for up to 1 h of operation has been demonstrated with reasonable faradaic efficiencies for measured O production. The properties of organic chromophores necessary for successfully driving water oxidation in a light-driven system are explored along with strategies for improving device performance.

A Full‐Spectrum Metal‐Free Porphyrin Supramolecular Photocatalyst for Dual Functions of Highly Efficient Hydrogen and Oxygen Evolution

“…As a result, organic photocatalysts are attracting increasing interest from researchers. In particular, several organic dye molecules have been developed as photocatalysts due to their large delocalization system and high spectrum efficiency . Unfortunately, the performance of completely organic photocatalyst at present still does not match that of the inorganic materials.…”

Stabilized photoanodes for water oxidation by integration of organic dyes, water oxidation catalysts, and electron-transfer mediators

“…in SI Appendix, Fig. S1 (19). As obtained by cyclic voltammetry measurements, E 1/2 values for Org1 •+/0 and Org2 •+/0 in aqueous 0.1 M KPF 6 are ∼1.04 and 1.03 V versus NHE, with some uncertainty in the values from kinetic distortions in the voltammograms.…”

“…In dye-sensitized solar cell applications, Ru(II) polypyridyl dyes have dominated as light absorbers, but organic dyes have also been used (12)(13)(14)(15)(16)(17)(18). For DSPECs, significant limitations can arise from the instabilities of the oxidized forms of the dyes in aqueous solution (19)(20)(21). Recently, we reported water oxidation from surfaces with organic push-pull dyes with an added WOC (19,22).…”

“…For DSPECs, significant limitations can arise from the instabilities of the oxidized forms of the dyes in aqueous solution (19)(20)(21). Recently, we reported water oxidation from surfaces with organic push-pull dyes with an added WOC (19,22). The combined light-absorber/catalyst electrodes led to water oxidation but with limited lifetimes because of the instabilities of the cationic forms of the chromophores in water, although stabilization of the dyes on the surface of TiO 2 by atomic layer deposition (ALD) of Al 2 O 3 has been reported (19,20).…”

Molecular Organic Sensitizers for Photoelectrochemical Water Splitting

“…The authors hypothesized that the oxidatively‐induced decomposition of the organic dye (in particular, the bithiophene sub‐unit) might explain the sustained photocurrents with low O 2 production, with the degradation of the oxidized dye possibly competing with the four‐electrons process of water oxidation. In order to reduce the dye degradation, three triarylamine‐based dyes without the thiophene spacers were investigated, using the core/shell SnO 2 /TiO 2 electrode . The modified dyes achieved a significantly higher FE of almost 80 %.…”