Physicochemical insights into semiconductor properties of a semitransparent tantalum nitride photoanode for solar water splitting

Tomohiro Higashi; Hiroshi Nishiyama; Yuriy Pihosh; Kaisei Wakishima; Yudai Kawase; Yutaka Sasaki; Akira Nagaoka; Kenji Yoshino; Kazuhiro Takanabe; Kazunari Domen

doi:10.1039/d3cp02563b

Physicochemical insights into semiconductor properties of a semitransparent tantalum nitride photoanode for solar water splitting

Phys Chem Chem Phys. 2023 Aug 2;25(30):20737-20748. doi: 10.1039/d3cp02563b.

Authors

Tomohiro Higashi¹, Hiroshi Nishiyama², Yuriy Pihosh², Kaisei Wakishima³, Yudai Kawase⁴, Yutaka Sasaki⁴, Akira Nagaoka^{3

5}, Kenji Yoshino³, Kazuhiro Takanabe⁴, Kazunari Domen^{2

6}

Affiliations

¹ Institute for Tenure Track Promotion, University of Miyazaki, 1-1 Gakuen-kibanadai-nishi, Miyazaki 889-2192, Japan. t_higashi@cc.miyazaki-u.ac.jp.
² Office of University Professors, The University of Tokyo, 2-11-16 Yayoi, Bunkyo-ku, Tokyo 113-8656, Japan. domen@chemsys.t.u-tokyo.ac.jp.
³ Electrical and Electronic Engineering Program, Faculty of Engineering, University of Miyazak, 1-1 Gakuen-kibanadai-nishi, Miyazaki 889-2192, Japan.
⁴ Department of Chemical System Engineering, School of Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656, Japan.
⁵ Research Center for Sustainable Energy & Environmental Engineering, University of Miyazaki, 1-1 Gakuen-kibanadai-nishi, Miyazaki 889-2192, Japan.
⁶ Research Initiative for Supra-Materials, Shinshu University, 4-17-1 Wakasato, Nagano 380-8533, Japan.

PMID: 37490272
DOI: 10.1039/d3cp02563b

Abstract

The self-conductivity of tantalum nitride (Ta₃N₅) thin film-based semitransparent photoanodes was found to promote the current originating from the photoelectrochemical oxygen evolution reaction (PEC OER) without a conducting substrate. With surface modification by the NiFeO_x-electrocatalyst, an optimized Ta₃N₅ thin film fabricated directly on a transparent insulating quartz substrate generated a photocurrent density of ∼5.9 ± 0.1 mA cm^-2 at 1.23 V vs. the reversible hydrogen electrode under simulated AM 1.5G solar illumination. The correlation between the PEC OER performance of NiFeO_x-modified Ta₃N₅ photoanodes and the electrical properties of Ta₃N₅ thin films was investigated based on the Hall effect measurements. By changing the nitridation conditions, these properties can be tuned so that the higher the Hall mobility (0.2 to 1.7 cm² V^-1 s^-1) and the lower the carrier concentration (10²⁰ to 10¹⁹ cm^-3). The surface chemical states of Ta₃N₅ thin films were investigated using X-ray photoelectron spectroscopy as a means of evaluating surface oxygen impurities and nitrogen vacancies, which may correlate with the PEC OER performance and the electrical properties of the material.