Nanoparticulate TiN Loading to Promote Z‐Scheme Water Splitting Using a Narrow‐Bandgap Nonoxide‐Based Photocatalyst Sheet

Some oxide‐based particulate photocatalyst sheets exhibit excellent activity during the water‐splitting reaction. The replacement of oxide photocatalysts with narrow‐bandgap photocatalysts based on nonoxides could provide the higher solar‐to‐hydrogen energy conversion efficiencies that are required for practical implementation. Unfortunately, the activity of nonoxide‐based photocatalyst sheets is low in many cases, indicating the need for strategies to improve the quality of nonoxide photocatalysts and the charge transfer process. In this work, single‐crystalline particulate SrTaO 2 N is studied as an oxygen evolution photocatalyst for photocatalyst sheets applied to Z‐scheme water splitting, in combination with La 5 Ti 2 Cu 0.9 Ag 0.1 O 7 S 5 and Au as the hydrogen evolution photocatalyst and conductive layer, respectively. The loading of SrTaO 2 N with CoO x provided increases activity during photocatalytic water oxidation, giving an apparent quantum yield of 15.7% at 420 nm. A photocatalyst sheet incorporating CoO x ‐loaded SrTaO 2 N is also found to promote Z‐scheme water splitting under visible light. Notably, the additional loading of nanoparticulate TiN on the CoO x ‐loaded SrTaO 2 N improves the water splitting activity by six times because the TiN promotes electron transfer from the SrTaO 2 N particles to the Au layer. This work demonstrates key concepts related to the improvement of nonoxide‐based photocatalyst sheets based on facilitating the charge transfer process through appropriate surface modifications.