Particulate photocatalyst sheets for efficient and scalable solar water splitting

Qian Wang^a^,^b, Takashi Hisatomi^a^,^b, Taro Yamada^a^,^b, Kazunari Domen^a^,^b, Qinxing Jia^a^,^b, Hiromasa Tokudome^b^,^c, Akihiko Kudo^d

^aJapan Technological Research Association of Artificial Photosynthetic Chemical Process, 2-11-9 Iwamotocho, Chiyoda-ku, 101-0032 Tokyo, Japan

^bTOTO Ltd., 2-8-1 Honson, Chigasaki, 253-8577 Kanagawa, Japan

^cTokyo University of Science, Japan, Tokyo, Japan

Materials for Sustainable Development Conference (MATSUS)
Proceedings of September Meeting 2016 (NFM16)

Berlin, Germany, 2016 September 5th - 13th

Organizers: Marin Alexe, Enrique Cánovas, Celso de Mello Donega, Ivan Infante, Thomas Kirchartz, Maksym Kovalenko, Federico Rosei, Lukas Schmidt-Mende, Laurens Siebbeles, Peter Strasser, Teodor K Todorov, Roel van de Krol and Ulrike Woggon

Oral, Takashi Hisatomi, presentation 010
Publication date: 14th June 2016

Z-scheme water splitting that uses two different photocatalysts for hydrogen and oxygen evolution is a promising approach to harvesting solar energy as chemical energy, because narrow band gap photocatalysts that are active either for water reduction or oxidation can be applied. It is critical to establish efficient electron transfer between a hydrogen evolution photocatalyst (HEP) and an oxygen evolution photocatalyst (OEP) without deteriorating their intrinsic photocatalytic properties in developing efficient Z-scheme water splitting systems.

Herein, we report a photocatalyst sheet, denoted as HEP/M/OEP, based on particulate HEP and OEP embedded into conductive materials (M) for efficient and scalable Z-scheme water splitting [1]. Particulate La- and Rh-codoped SrTiO₃ (SrTiO₃:La,Rh) and BiVO₄ were employed as HEP and OEP, respectively, and were embedded into Au thin layer by a particle transfer method. The SrTiO₃:La,Rh/Au/BiVO₄ photocatalyst sheet exhibited activities for overall water splitting 6 and 20 times higher than the suspension of the SrTiO₃:La,Rh and BiVO₄ photocatalysts and the SrTiO₃:La,Rh/BiVO₄ sheet without conductive materials, respectively. The SrTiO₃:La,Rh/Au/BiVO₄ photocatalyst sheet achieved an apparent quantum yield (AQY) of 5.9% under 418-nm monochromatic light irradiation and a solar-to-hydrogen energy conversion efficiency (STH) of 0.2%. Recently, pure water splitting with a STH of 1.1% and an AQY of over 30% at 419 nm were achieved through optimization of sheet preparation and water splitting reaction conditions [2].

The SrTiO₃:La,Rh/Au/BiVO₄ photocatalyst sheet exhibited high activity even in pure water without any additives or solution mixing unlike (photo)electrochemical systems that necessitate highly concentrated supporting electrolytes and buffering reagents and conventional Z-scheme systems that require reversible redox couples or careful adjustment of pH values. On the photocatalyst sheet, HEP and OEP particles are physically embedded into conductive layer in the immediate vicinity. This configuration is effective in suppressing the generation of concentration overpotentials of H⁺/OH^- and IR drops between the hydrogen and oxygen evolution sites, while the Au layer effectively transfers photogenerated electrons from BiVO₄ to SrTiO₃:La,Rh. Therefore, the photocatalyst sheet with high activity is scalable as is. The photocatalyst sheet design will enable efficient and scalable water splitting using particulate semiconductors.

[1] Wang et al., J. Catal. 2015, 328 308.[2] Wang et al., Nat. Mater. doi:10.1038/nmat4589.

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