Solar-Driven Photoelectrochemical Water Oxidation over an n-Type Lead-Titanium Oxyfluoride Anode

Naoki Hirayama; Hiroko Nakata; Haruki Wakayama; Shunta Nishioka; Tomoki Kanazawa; Ryutaro Kamata; Yosuke Ebato; Kosaku Kato; Hiromu Kumagai; Akira Yamakata; Kengo Oka; Kazuhiko Maeda

doi:10.1021/jacs.9b06570

Solar-Driven Photoelectrochemical Water Oxidation over an n-Type Lead-Titanium Oxyfluoride Anode

J Am Chem Soc. 2019 Oct 30;141(43):17158-17165. doi: 10.1021/jacs.9b06570. Epub 2019 Oct 17.

Authors

Affiliations

¹ Department of Chemistry, School of Science , Tokyo Institute of Technology , 2-12-1-NE-2 Ookayama , Meguro-ku, Tokyo 152-8550 , Japan.
² Japan Society for the Promotion of Science , Kojimachi Business Center Building , 5-3-1 Kojimachi , Chiyoda-ku, Tokyo 102-0083 , Japan.
³ Graduate School of Engineering , Toyota Technological Institute , 2-12-1 Hisakata , Tempaku, Nagoya 468-8511 , Japan.
⁴ Department of Applied Chemistry, Faculty of Science and Engineering , Chuo University , Bunkyo-ku, Tokyo 112-8551 , Japan.

PMID: 31588742
DOI: 10.1021/jacs.9b06570

Abstract

Mixed-anion compounds (e.g., oxynitrides and oxysulfides) are potential candidates as photoanodes for visible-light water oxidation, but most of them suffer from oxidative degradation by photogenerated holes, leading to low stability. Here we show an exceptional example of a stable, mixed-anion water-oxidation photoanode that consists of an oxyfluoride, Pb₂Ti₂O_5.4F_1.2, having a band gap of ca. 2.4 eV. Pb₂Ti₂O_5.4F_1.2 particles, which were coated on a transparent conductive glass (FTO) support and were subject to postdeposition of a TiO₂ overlayer, generated an anodic photocurrent upon band gap photoexcitation of Pb₂Ti₂O_5.4F_1.2 (λ <520 nm) with a rather negative photocurrent onset potential of ca. -0.6 V vs NHE, which was independent of the pH of the electrolyte solution. Stable photoanodic current was observed even without loading a water oxidation promoter such as CoO_x. Nevertheless, loading CoO_x onto the TiO₂/Pb₂Ti₂O_5.4F_1.2/FTO electrode further improved the anodic photoresponse by a factor of 2-3. Under AM1.5G simulated sunlight (100 mW cm^-2), stable water oxidation to form O₂ was achieved using the optimized Pb₂Ti₂O_5.4F_1.2 photoanode in the presence of an applied potential smaller than 1.23 V, giving a Faradaic efficiency of 93% and almost no sign of deactivation during 4 h of operation. This study presents the first example of photoelectrochemical water splitting driven by visible-light excitation of an oxyfluoride that stably works, even without a water oxidation promoter, which is distinct from ordinary mixed-anion photoanodes that usually require a water oxidation promoter.