Ta₃N₅ Nanosheets Derived from TaS₂ as Efficient Photocatalysts for Water Oxidation

The morphology and crystalline structure of semiconductor materials both play important roles in determining the photocatalytic activity of such materials. In this regard, tantalum nitride (Ta₃N₅) shows promise as a visible-light-responsive photocatalyst for solar-driven water splitting. Even so, the performance of this material is limited by its bulk morphology and by high defect densities and inefficient charge transport. The present work synthesized single-crystalline Ta₃N₅ nanosheets having reduced defect concentrations and an increased specific surface area via the direct nitridation of two-dimensional TaS₂ nanosheets. The Ta₃N₅ nanosheets had a thickness of approximately 30 nm with well-defined exposed facets and a uniform single-crystalline structure, and so led to a shorter charge-carrier diffusion length along with efficient charge separation and transport. When modified with IrO_x as a cocatalyst, these nanosheets provided an apparent quantum yield of 32.4% at 420 nm during photocatalytic oxygen evolution with sacrificial electron acceptors, outperforming Ta₃N₅ synthesized from Ta₂O₅. This material was also integrated into Z-scheme photocatalyst sheets together with La₅Ti₂Cu_0.9Ag_0.1O₇S₅ as the hydrogen evolution photocatalyst and carbon nanotubes as the electron mediator. These sheets enabled overall water splitting with stoichiometric H₂ and O₂ evolution in response to visible light, with a light absorption range extended to approximately 600 nm. This work underscores the critical roles of precursor selection and nanoscale morphological control in the development of photocatalysts with minimal defects and provides new insights expected to advance the field of solar-to-chemical energy conversion.