Proceedings of Online nanoGe Fall Meeting 20 (OnlineNFM20)
Publication date: 4th October 2020
Sunlight-driven water splitting is studied actively for production of renewable solar hydrogen [1]. Both the efficiency and the scalability of water-splitting systems are essential factors for practical utilization of renewable solar hydrogen. It is desirable to develop particulate photocatalysts and their reaction systems that efficiently split water, because particulate photocatalyst systems can be spread over wide areas by inexpensive processes potentially.
The author has studied various oxide, (oxy)nitride, and (oxy)chalcogenide photocatalysts [2]. The water splitting activity of SrTiO3 can be improved by two orders of magnitude by doping Al. The quantum efficiency of photocatalytic overall water splitting has reached almost unity in the near UV region [3]. This is the highest reported to date and confirms that particulate photocatalysts can drive the uphill overall water splitting reaction as efficiently as the photon-to-chemical conversion process in photosynthesis.
The author has also been developing panel reactors for large-scale applications. A prototype panel reactor containing Al-doped SrTiO3 photocatalyst sheets splits water and releases product H2 and O2 gas bubbles at a rate expected at a solar-to-hydrogen energy conversion efficiency (STH) of 10% under intense UV illumination [4]. A 1-m2-sized photocatalyst panel reactor splits water under natural sunlight irradiation without a significant loss of the intrinsic activity of the photocatalyst sheets. A larger size (100 m2) solar hydrogen production system was constructed and its performance and system characteristics are currently under investigation.
To realize a sufficient STH, it is essential to develop photocatalysts active under visible light irradiation. Ta3N5 [5] and Y2Ti2O5S2 [6] show activity in overall water splitting via one-step excitation under visible light irradiation. Photocatalyst sheets consisting of La- and Rh-codoped SrTiO3 and Mo-doped BiVO4 split water into H2 and O2 via two-step excitation, referred to as Z-scheme, and exhibit STH exceeding 1.0% [7,8]. Some other (oxy)chalcogenides and (oxy)nitrides with longer absorption edge wavelengths are also applicable to Z-schematic photocatalyst sheets.
In my talk, the latest progress in photocatalytic materials and reactors will be presented.
[1] Hisatomi et al. Nat. Catal. 2019, 2, 387.
[2] Chen et al. Nat. Rev. Mater. 2017, 2, 17050.
[3] Takata et al. Nature, 2020, 581, 411.
[4] Goto et al. Joule 2018, 2, 509.
[5] Wang et al. Nat. Catal. 2018, 1, 756.
[6] Wang et al. Nat. Mater. 2019, 18, 827.
[7] Wang et al. Nat. Mater. 2016, 15, 611.
[8] Wang et al. J. Am. Chem. Soc. 2017, 139, 1675.
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