Elementary Steps in the photocatalytic Water Splitting over TiO2-based Model Electrode Systems

通过光诱导分解水制氢是可持续能源经济的一种有前途的途径，尽管迄今为止还没有确定具有成本效益的光催化系统。人们相信，成功地寻找新的和改进的光催化剂将基于对光催化水分解中的所有基元反应步骤的分子理解。在本项目中，将制备基于单晶TiO 2（110）和TiO 2（011）的光催化水分解模型系统，并通过表面敏感方法（原位）以及理论（从头算）光电化学方法进行广泛表征。单一的结晶度的模型系统是必需的，允许从头计算与相应的实验进行直接比较。选择TiO 2作为光催化剂材料的动机是其活性，无毒，无所不在，廉价且在光化学反应条件下稳定。这些先决条件对于未来氢燃料经济的发展是不可或缺的。然而，TiO2对于太阳光的量子效率相当低，因为带隙相当宽，超过3eV。除了通过掺杂N和Cr等杂质进行带隙工程外，最近发现的带隙仅为2.1eV的无掺杂剂TiO 2（011）相将成为本项目的重点。水的光催化分解中的速率决定部分是析氧反应（由于4电子过程：OER）。因此，助催化剂，如RuO2，已知用于OER的最佳催化剂，经常被共同添加。基于单晶TiO 2的模型光催化剂和纳米RuO2膜的组合系统提供了对界面的原子尺度控制，这反过来又非常有利于电子和结构表征以及光诱导OER中的基元反应步骤的识别。

Hydrogen production through photo-induced splitting of water is a promising avenue for sustainable energy economy, although no cost-effective photocatalytic system has been identified so far. It is believed that a successful search for a new and improved photocatalyst will be based on a molecular understanding of all elementary reaction steps in the photocatalytic water splitting. In the present project model systems for photocatalytic water splitting on the basis of single-crystalline TiO2(110) and TiO2(011) will be prepared and extensively characterized by surface sensitive methods (in-situ) as well as theoretical (ab-initio) photo-electrochemical methods. Single crystallinity of the model systems is required to allow for a direct comparison of ab-initio calculations with corresponding experiments. The choice of TiO2 as photocatalyst material is motivated by its activity, being non-toxic, omnipresent, inexpensive and stable under photochemical reaction conditions. These preconditions are indispensable for the development of a future hydrogen fuel economy. However, the quantum efficiency of TiO2 for sun light is quite low as the band gap is quite wide with more than 3eV. Besides band gap engineering by doping with impurities such as N and Cr, the recently discovered dopant-free TiO2 phase on TiO2(011) with a band gap of only 2.1eV will be in the focus of the present project. The rate determining part in the photocatalytic splitting of water is the oxygen evolution reaction (due to the 4-electron process: OER). Therefore co-catalysts, such as RuO2, the best catalyst known for OER, are frequently co-added. The combined system of single crystalline TiO2-based model photocatalysts and ultrathin RuO2 films provides atomic-scale control of the interface that in turn is highly beneficial for electronic and structural characterization as well as the identification of elementary reaction steps in the photo-induced OER.