Activation of Nonoxide Photocatalyst Sheet Operable under Visible Light Irradiation up to 600 nm by Conductive Bilayer

Particulate photocatalyst sheets allow for scalable sunlight-driven overall water splitting. Photocatalyst sheets composed of doped-La5Ti2Cu0.9Ag0.1O7S5 (LTCA), gallium zinc oxynitride (GaN:ZnO), and Au as the hydrogen evolution photocatalyst, oxygen evolution photocatalyst, and conductor layer, respectively, are promising candidates because of their long absorption edge wavelengths (700 and 600 nm, respectively). However, the actual performance of this sheet has been poor due to the large Schottky barrier at the GaN:ZnO/Au interface. Here, we developed a photocatalyst sheet incorporating conductive thin Au and thick Ti bilayer films having high and low work functions, respectively, which increased the activity by a factor of 6 compared with that of a single Au layer sheet. An optimized doped-LTCA/Au/Ti/CoOx/GaN:ZnO sheet modified with CoOx and Cr2O3/Rh cocatalysts exhibited a solar-to-hydrogen energy conversion efficiency of 0.3%. This work provides a key strategy based on the utilization of narrow bandgap oxynitride materials to construct efficient visible-light-driven nonoxide-based sheets.