The design of type-II van der Waals (vdW) heterostructures is regarded as a promising route to produce green hydrogen via photocatalytic water splitting. To this aim, we propose novel vertically stacked vdW heterostructures based on ZnO and Janus VXY (X = Br, Cl, Y = Se, and Te) phases, and investigate their optoelectronic properties and photocatalytic performance by means of density functional theory simulations. The thermal stability of the heterostructures is confirmed by ab initio molecular dynamics simulations at 300 K. The HSE06 calculated band structures show that a specific stacking of ZnO–VBrSe and ZnO–VClSe exhibits an indirect band gap with type-II band alignment, while all other stackings exhibit a direct band gap with type-I band alignment. The type-II band alignment, along with the difference in the work function and the electrostatic potential between the ZnO and VXY monolayer, will result in a built-in electric field direct from the ZnO monolayer to the VXY monolayer which is crucial for photogenerated charge separation, and prevents the charge recombinations. The optical absorption coefficient α of all the considered ZnO–VXY heterostructures displays the first excitonic peak in the energy range required for photocatalysis applications. Based on the band edge potential analysis, all the studied systems are capable of starting an oxygen evolution reaction spontaneously, while some external stimuli will be required to initiate the hydrogen evolution reaction. The reported results suggest that the proposed ZnO–VXY vdW heterostructures have great potential for photocatalysis and optoelectronic device applications.

中文翻译：

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ZnO-Janus van der Waals 异质结构中光催化活性的第一性原理研究


II 型范德华 （vdW） 异质结构的设计被认为是通过光催化分解水生产绿色氢的一条有前途的路线。为此，我们提出了基于 ZnO 和 Janus VXY （X = Br、Cl、Y = Se 和 Te） 相的新型垂直堆叠 vdW 异质结构，并通过密度泛函理论模拟研究了它们的光电性质和光催化性能。异质结构的热稳定性通过 300 K 下的从头分子动力学模拟得到证实。HSE06 计算的能带结构表明，ZnO-VBrSe 和 ZnO-VClSe 的特异性堆叠表现出具有 II 型能带对准的间接带隙，而所有其他堆叠表现出具有 I 型能带对准的直接带隙。II 型能带排列，以及 ZnO 和 VXY 单层之间的功函数和静电势的差异，将导致从 ZnO 单层直接到 VXY 单层的内置电场，这对于光生电荷分离至关重要，并防止电荷复合。所有考虑的 ZnO-VXY 异质结构的光吸收系数α显示光催化应用所需能量范围内的第一个激子峰。基于带边电位分析，所有研究的系统都能够自发地启动析氧反应，而需要一些外部刺激来启动析氢反应。报道的结果表明，所提出的 ZnO-VXY vdW 异质结构在光催化和光电器件应用中具有很大的潜力。