Metal-free carbazole–thiophene photosensitizers designed for a dye-sensitized H2-evolving photocatalyst in Z-scheme water splitting

Author:

Nakada Akinobu12ORCID,Yokota Takayuki1,Ogura Morihiko3ORCID,Chang Ninghui3ORCID,Tomita Osamu1,Saeki Akinori4ORCID,Ogasawara Masamichi5ORCID,Abe Ryu1ORCID

Affiliation:

1. Department of Energy and Hydrocarbon Chemistry, Graduate School of Engineering, Kyoto University 1 , Nishikyo-ku, Kyoto 615-8510, Japan

2. PRESTO, Japan Science and Technology Agency (JST) 2 , Kawaguchi, Saitama 332-0012, Japan

3. Catalysis Research Center and Graduate School of Life Science, Hokkaido University 3 , Kita-ku, Sapporo 001-0021, Japan

4. Department of Applied Chemistry, Graduate School of Engineering, Osaka University 4 , 2-1 Yamadaoka, Suita, Osaka 565-0871, Japan

5. Department of Natural Science, Graduate School of Science and Technology, Tokushima University 5 , Tokushima 770-8506, Japan

Abstract

Dye-sensitized photocatalysts with molecular dyes and widegap semiconductors have attracted attention because of their design flexibility, for example, tunable light absorption for visible-light water splitting. Although organic dyes are promising candidates as metal-free photosensitizers in dye-sensitized photocatalysts, their efficiency in H2 production has far been unsatisfactory compared to that of metal-complex photosensitizers, such as Ru(II) tris-diimine-type complexes. Here, we demonstrate the substantial improvement of carbazole–thiophene-based dyes used for dye-sensitized photocatalysts through systematic molecular design of the number of thiophene rings, substituents in the thiophene moiety, and the anchoring group. The optimized carbazole–thiophene dye-sensitized layered niobate exhibited a quantum efficiency of 0.3% at 460 nm for H2 evolution using a redox-reversible I− electron donor, which is six-times higher than that of the best coumarin-based metal-free dye reported to date. The dye-sensitized photocatalyst also facilitated overall water splitting when combined with a WO3-based O2-evolving photocatalyst and an I3−/I− redox shuttle mediator. The present metal-free dye provided a high dye-based turnover frequency for water splitting, comparable to that of the state-of-the-art Ru(II) tris-diimine-type photosensitizer, by simple adsorption onto a layered niobate. Thus, this study highlights the potential of metal-free organic dyes with appropriate molecular designs for the development of efficient water splitting.

Funder

Japan Science and Technology Agency

Japan Society for the Promotion of Science

Publisher

AIP Publishing

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