Solvation and Charge Transfer Processes at Semiconductor/Liquid Water Interfaces

金属氧化物和液态水之间的界面在从多相催化到生物过程的许多系统中起着至关重要的作用。尤其重要的是电荷在界面上的转移过程，因为金属氧化物能够催化发生在相邻液相中的反应。一个很有前途的应用是光催化水分解成氢和氧。在这个过程中，光子被金属氧化物吸收，获得的能量被用来分解表面的水。因此，这个过程可以用来生产碳中性燃料。尽管它的相关性，只有很少的信息，确切的分子过程在界面上。例如，水分子是如何与氧化物相互作用的，以及电荷是如何在界面上定位的，这是特别有趣的。这些问题可以用计算化学的方法来解决，特别是从头算分子动力学（AIMD）。这些方法能够在原子水平上真实地模拟氧化物/水界面的结构动力学。尽管如此，即使对现代高性能计算机来说，模拟也是具有挑战性的，因为氧化物/水界面的电子结构非常复杂。因此，本项目将使用“机器学习”方法来加速AIMD仿真。该项目的最终目标是深入了解微观性质，例如给定金属氧化物表面液态水和载流子的结构、动力学和反应性。本文选择WO3作为模型体系，认为它是一种很有前途的材料，可以作为析氧反应的光活性电极。得到的关于WO3/水界面的见解可以推广到预测其他金属氧化物/水界面的性质。此外，AIMD模拟补充了现有的实验数据，也是在微观水平上理解实验的重要贡献。

Interfaces between metal oxides and liquid water play a crucial role for numerous systems ranging from heterogeneous catalysis to biological processes. Especially important are charge transfer processes across the interface because the metal oxide is able to catalyze reactions which occur in the adjacent liquid phase. A promising application is photocatalytic water splitting into hydrogen and oxygen. During this process, photons are absorbed by the metal oxide and the gained energy is used to split water at its surface. The process can thus be utilized to generate carbon-neutral fuel. Despite its relevance there is only little information about the exact molecular processes at the interface. For example, it is especially interesting how water molecules interact with the oxide in detail as well as how and where charges are localized at the interface. Those questions can be addressed using methods of computational chemistry, in particular ab initio molecular dynamics~(AIMD). These methods are able to realistically model the structural dynamics of an oxide/water interface at the atomistic level. Still, the simulations are challenging, even for modern high-performance computers, since the electronic structure of oxide/water interfaces is highly complex. Therefore, “machine learning” approaches are to be used in this project to accelerate the AIMD simulations. The ultimate goal of the project is to gain a deep understanding of microscopic properties, such as structure, dynamics and reactivity of liquid water and charge carriers at a given metal oxide surface. Here, WO3 is chosen as the model system being a promising material to act as a photoactive electrode for the oxygen evolution reaction. The obtained insights on the WO3/water interface are then to be generalized to predict properties of other metal oxide/water interfaces. Moreover, the AIMD simulations complement existing experimental data and are also an integral contribution to understand experiments at the microscopic level.