Electro-assembly of a Chromophore-Catalyst Bilayer for Water Oxidation and Photocatalytic Water Splitting.

Ashford DL, Sherman BD, Binstead RA, Templeton JL, Meyer TJ.

Angew Chem Int Ed Engl. 2015 Apr 13;54(16):4778-81.

Department of Chemistry, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599, United States.

 

Abstract

The use of electropolymerization to prepare electrocatalytically and photocatalytically active electrodes for water oxidation is described. Electropolymerization of the catalyst Ru(II) (bda)(4-vinylpyridine)2 (bda=2,2′-bipyridine-6,6′-dicarboxylate) on planar electrodes results in films containing semirigid polymer networks. In these films there is a change in the water oxidation mechanism compared to the solution analogue from bimolecular to single-site. Electro-assembly construction of a chromophore-catalyst structure on mesoporous, nanoparticle TiO2 films provides the basis for a dye-sensitized photoelectrosynthesis cell (DSPEC) for sustained water splitting in a pH 7 phosphate buffer solution. Photogenerated oxygen was measured in real-time by use of a two-electrode cell design.

© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

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Significance Statement

Artificial photosynthesis is one of the holy grails of renewable energy. It combines solar energy conversion and energy storage by using the energy of the sun to drive chemical reactions which produce solar fuels – hydrogen from water splitting, reduced carbon fuels from CO2. In an approach that we have pioneered, the dye-sensitized photoelectrochemical cell (DSPEC), the basic photochemical principles underlying natural photosynthesis are combined with high band gap oxide semiconductors in a device architecture. A light harvesting molecular light absorber undergoes light absorption and electron injection into the oxide, transferring oxidative equivalents to a catalyst and activating it toward water oxidation.

In past experiments, the preparation of pre-formed chromophore-catalyst assemblies has typically been difficult and time consuming, greatly limiting progress in this area. We report here a new approach in which covalently linked assemblies are created directly on the surface of the oxide, sidestepping multi-step syntheses and complex separation and purification procedures. It uses an “electro-assembly” technique to form covalent bonds between the chromophore, pre-surface bound to the oxide, and the catalyst in an external solution.

 

In the results that we recently reported, detailed mechanistic insight was gained into how water oxidation occurs with clear evidence found for a single-site mechanism on the surface. This is in contrast to earlier results in acidic solution which pointed to a bimolecular mechanism. With the surface-bound electro-assembly, we were also able to demonstrate light-driven water oxidation with the real-time measurement of photo-generated oxygen at electro-assembly/photo-anode by using an in situ photoelectrochemical-collector electrode design with hydrogen produced at a separate cathode. This is an important step forward in our quest to use the DSPEC as a way to obtain efficient, sustained photoelectrochemical water splitting into hydrogen and oxygen.

Electro-Assembly of a Chromophore-Catalyst Bilayer for Water Oxidation and Photocatalytic Water Splitting. Advances In Engineering