Abstract
Novel two-dimensional (2D) materials have received extensive attention in the field of photocatalysis due to their unique properties. Traditional ZnO material with wurtzite structure transforms into a stable graphite-like structure that has the characteristics of 2D material when its thickness is less than a few atomic layers. In this work, using first-principles calculations, we investigated the potential of multilayer graphite-like ZnO as a photocatalyst for water splitting. The results showed that multilayer ZnO is a series of direct bandgap semiconductors, and their band edge positions all straddle the redox potential of water. Increasing with the number of layers, the bandgap of multilayer ZnO decreased from 3.20 eV for one layer to 2.21 eV for six layers, and visible light absorption capacity was significantly enhanced. Hence, multilayer ZnO was indeed promising for photocatalytic water splitting. Furthermore, suitable biaxial tensile strain could decrease the bandgap and maintain the stable graphite-like structure at a broader thickness range. In contrast, excessive biaxial tensile strain could change the redox capacity of multilayer ZnO and prevent it from catalyzing water splitting. Our theoretical results show that six-layer ZnO under 1% biaxial strain had direct bandgap of 2.07 eV and represents the most excellent photocatalytic performance among these multilayer ZnO materials.
Highlights
As a possible way to alleviate the energy crisis, photocatalytic water splitting to produce hydrogen has attracted more and more attention [1,2]
In this article, using first-principles calculations, we investigated the photocatalytic performance of multilayer ZnO combined with biaxial strain
By applying biaxial strain to multilayer ZnO, we found that 1% biaxial tensile strain reduced the bandgap of six-layer ZnO from 2.21 to 2.07 eV, Catalysts 2020, 10, x FOR PEER REVIEW
Summary
As a possible way to alleviate the energy crisis, photocatalytic water splitting to produce hydrogen has attracted more and more attention [1,2]. Since utilizing solar energy to generate photogenerated electron-hole pairs could participate in the redox reaction on the surface of the material to catalyze water splitting, synthesizing and developing efficient photocatalysts has great significance for hydrogen production. High-efficiency photocatalysts in solar energy conversion applications need a suitable bandgap that can absorb visible light energy, and their band edge position must straddle the redox potential of water to ensure sufficient redox capacity [3]. ZnO is a potential photocatalytic material with a proper bandgap and has been widely investigated, owing to its high carrier mobility and excellent optical characteristics [4]. Compared with the bulk structure, 2D ZnO has a larger specific surface area and Catalysts 2020, 10, 1208; doi:10.3390/catal10101208 www.mdpi.com/journal/catalysts
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