Yan Zhao, Zhenming Tian, Qisen Jia, Ting Yao, Jiashu Li, Yanan Wang, Xuejing Cui, Jing Liu*, Xin Chen*, Luhua Jiang*

Cite this article: Chin. J. Struct. Chem., 2025, 44(7), 100619. DOI: 10.1016/j.cjsc.2025.100619

Publication date: July 1, 2025

Keywords: Photoelectrocatalytic water oxidation; Selectivity; Crystal orientation engineering; Operando fourier transform infrared spectroscopy; Interfacial water structure

ABSTRACT

Photoelectrochemical water oxidation reaction (PEC-WOR) as a sustainable route to produce H2O2 is attractive but limited by low activity and poor product selectivity of photoanodes due to limited photogenerated charge efficiency and unfavorable thermodynamics. Herein, by crystal orientation engineering, the WO3 photoanode exposing (200) facets achieves both superior WOR activity (15.4 mA cm-2 at 1.76 VRHE) and high selectivity to H2O2 (∼70%). Comprehensive experimental and theoretical investigations discover that the high PEC-WOR activity of WO3-(200) is attributed to the rapid photogenerated charge separation/transfer both in bulk and at interfaces of WO3 (200) facet, which reduces the charge transfer resistance. This, coupling with the unique defective hydrogen bonding network at the WO3-(200)/electrolyte interface evidenced by operando PEC Fourier transform infrared spectroscopy, facilitating the outward-transfer of the WOR-produced H+, lowers the overall reaction barrier for the PEC-WOR. The superior selectivity of PEC-WOR to H2O2 is ascribed to the unique defective hydrogen bonding network alleviated adsorption of *OH over the WO3-(200) facet, which specially lowers the energy barrier of the 2-electron pathway, as compared to the 4-electron pathway. This work addresses the significant role of crystal orientation engineering on photoelectrocatalytic activity and selectivity, and sheds lights on the underlying PEC mechanism by understanding the water adsorption behaviors under illumination. The knowledge gained is expected to be extended to other photoeletrochemical reactions.