Transparent Ta3N5 Photoanodes for Efficient Oxygen Evolution toward the Development of Tandem Cells

• Published in: Angewandte Chemie International Edition Vol. 58; no. 8; pp. 2300 - 2304
• Main Authors: Higashi, Tomohiro, Nishiyama, Hiroshi, Suzuki, Yohichi, Sasaki, Yutaka, Hisatomi, Takashi, Katayama, Masao, Minegishi, Tsutomu, Seki, Kazuhiko, Yamada, Taro, Domen, Kazunari
• Format: Journal Article
• Language: English
• Published: Germany Wiley Subscription Services, Inc 18.02.2019
• Edition: International ed. in English
• Subjects: (oxy)nitrides; Chemical evolution; Copper indium selenides; Electrodes; Energy conversion; Energy conversion efficiency; Evolution; Gallium nitrides; Hydrogen; Hydrogen production; Hydrogen-based energy; Photoanodes; Photocathodes; Photoelectric effect; Photoelectric emission; photoelectrochemical tandem cell; photoelectrochemistry; Sapphire; Solar energy; solar energy conversion; Splitting; Substrates; Transparency; Water splitting; Wavelengths; photoelectrochemistry solar energy conversion water splitting photoelectrochemical tandem cell (oxy)nitrides
• ISSN: 1433-7851; 1521-3773
• DOI: 10.1002/anie.201812081

Photoelectrochemical water splitting is regarded as a promising approach to the production of hydrogen, and the development of efficient photoelectrodes is one aspect of realizing practical systems. In this work, transparent Ta3N5 photoanodes were fabricated on n‐type GaN/sapphire substrates to promote O2 evolution in tandem with a photocathode, to realize overall water splitting. Following the incorporation of an underlying GaN layer, a photocurrent of 6.3 mA cm−2 was achieved at 1.23 V vs. a reversible hydrogen electrode. The transparency of Ta3N5 to wavelengths longer than 600 nm allowed incoming solar light to be transmitted to a CuInSe2 (CIS), which absorbs up to 1100 nm. A stand‐alone tandem cell with a serially‐connected dual‐CIS unit terminated with a Pt/Ni electrode was thus constructed for H2 evolution. This tandem cell exhibited a solar‐to‐hydrogen energy conversion efficiency greater than 7 % at the initial stage of the reaction. A transparent Ta3N5 photoanode was fabricated on GaN/Al2O3 substrate to develop the tandem cell for overall water splitting. The transparency of Ta3N5/GaN/Al2O3 to wavelengths longer than 600 nm allowed incoming solar light to be transmitted to a CuInSe2 (CIS). A stand‐alone tandem cell with a serially‐connected dual‐CIS‐based cathode was constructed. This tandem cell exhibited an initial solar‐to‐hydrogen energy conversion efficiency of 7 %.