Application of LaMg1/3Ta2/3O2N as a hydrogen evolution photocatalyst of a photocatalyst sheet for Z-scheme water splitting

Abstract

Z-scheme water splitting systems are suited for photocatalysts with long absorption edge wavelengths because H2 and O2 evolution reactions occur on different photocatalysts via two-step excitation. In this study, the applicability of LaMg1/3Ta2/3O2N, a 600-nm-class photocatalyst, as a H2 evolution photocatalyst (HEP) in Z-scheme systems was investigated. The redox-mediator-free Z-scheme system composed of RhCrOx/LaMg1/3Ta2/3O2N as a HEP and rutile as an O2 evolution photocatalyst (OEP) showed higher activity than one-step excitation systems of RhCrOx/LaMg1/3Ta2/3O2N or rutile alone under irradiation (λ≥300nm). Moreover, a photocatalyst sheet, which consisted of RhCrOx/LaMg1/3Ta2/3O2N and rutile embedded in a Au layer by the particle transfer method, exhibited a photocatalytic activity one order of magnitude higher than the Z-scheme powder suspension system, although LaMg1/3Ta2/3O2N suffered from self-oxidation. Coating the photocatalyst sheet with an amorphous titanium oxide (a-TiO2) protective layer suppressed the self-oxidation of LaMg1/3Ta2/3O2N effectively while maintaining a high photocatalytic activity. This is because the overlying a-TiO2 layer stabilized LaMg1/3Ta2/3O2N while the underlying Au layer transferred charges between RhCrOx/LaMg1/3Ta2/3O2N and rutile effectively. The present study demonstrates the feasibility of the use of LaMg1/3Ta2/3O2N in Z-scheme systems as a HEP with a long absorption edge wavelength and provides a facile approach to stabilizing oxynitrides in photocatalyst sheet systems.