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Issue 2, 2016
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Visible light-driven water oxidation using a covalently-linked molecular catalyst–sensitizer dyad assembled on a TiO2 electrode

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Abstract

The combination of porphyrin as a sensitizer and a ruthenium complex as a water oxidation catalyst (WOC) is promising to exploit highly efficient molecular artificial photosynthetic systems. A covalently-linked ruthenium-based WOC–zinc porphyrin (ZnP) sensitizer dyad was assembled on a TiO2 electrode for visible-light driven water oxidation. The water oxidation activity was found to be improved in comparison to the reference systems with the simple combination of the individual WOC and ZnP as well as with ZnP solely, demonstrating the advantage of the covalent linking approach over the non-covalent one. More importantly, via vectorial multi-step electron transfer triggered by visible light, the dye-sensitized photoelectrochemical cell (DSPEC) achieved a broader PEC response in the visible region than DSPECs with conventional ruthenium-based sensitizers. Initial incident photon-to-current efficiencies of 18% at 424 nm and 6.4% at 564 nm were attained under monochromatic illumination and an external bias of −0.2 V vs. NHE. Fast electron transfer from the WOC to the photogenerated radical cation of the sensitizer through the covalent linkage may suppress undesirable charge recombination, realizing the moderate performance of water oxidation. X-ray photoelectron spectroscopic analysis of the photoanodes before and after the DSPEC operation suggested that most of the ruthenium species exist at higher oxidation states, implying that the insufficient oxidation potential of the ZnP moiety for further oxidizing the intermediate ruthenium species at the photoanode is at least the bottleneck of the system.

Graphical abstract: Visible light-driven water oxidation using a covalently-linked molecular catalyst–sensitizer dyad assembled on a TiO2 electrode

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Publication details

The article was received on 28 Sep 2015, accepted on 09 Nov 2015 and first published on 30 Nov 2015


Article type: Edge Article
DOI: 10.1039/C5SC03669K
Chem. Sci., 2016,7, 1430-1439
  • Open access: Creative Commons BY-NC license
    All publication charges for this article have been paid for by the Royal Society of Chemistry

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    Visible light-driven water oxidation using a covalently-linked molecular catalyst–sensitizer dyad assembled on a TiO2 electrode

    M. Yamamoto, L. Wang, F. Li, T. Fukushima, K. Tanaka, L. Sun and H. Imahori, Chem. Sci., 2016, 7, 1430
    DOI: 10.1039/C5SC03669K

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