An Atomic Level Understanding of Optimal Characteristics of TiO2 Protection Layers and Photoelectrode/TiO2 Interfaces for Efficient and Stable Solar Fuel Production

美国威斯康辛大学麦迪逊分校教授崔景信（音译）和美国芝加哥大学教授朱利亚•加利（音译）在化学系化学催化项目的支持下，正在研究利用太阳能分解水并产生清洁燃料氢气的半导体电极。这些半导体电极被称为光电极，它们通常需要涂上一层保护层来增强其性能和稳定性。迄今为止，二氧化钛（TiO2）由于其惰性而成为使用最广泛的保护层材料。然而，文献中报道的有效TiO2保护层的最佳特性并不一致。Choi和Galli将使用实验和计算相结合的方法，努力从微观上理解不同的光电极- tio2界面如何影响整体光电极性能。该团队旨在阐明TiO2层的光电极依赖特性，以最佳地保护不同类型的光电极。该项目旨在实现最佳光电极/TiO2组件的合理设计，以实现高效和可持续的太阳能水分解。就更广泛的影响而言，Choi和Galli将维护一个包含经过验证的数据集的网站，这些数据集将被社区成员轻松访问和重用。该网站将加强基础设施，指导研究人员使用实验和计算相结合的方法来研究太阳能水分解和其他复杂系统。该项目还将在一个高度跨学科的环境中培养研究生，并在使用可再生太阳能的清洁燃料生产领域培养多才多艺的研究人员。根据该奖项，Choi（威斯康星大学）/ Galli（芝加哥大学）团队将研究利用太阳能分解水并产生清洁燃料氢气的光电极。Choi和Galli将使用紧密结合的实验和计算研究，目的是全面了解TiO2层的光电极依赖特性，以最佳地保护不同类型的光电极，同时最大化光电流和光电压的产生。该团队将阐明光电极/TiO2界面对能带对准和电子-空穴复合的影响。他们将分别使用n-BiVO4/TiO2， p-Cu2O/TiO2和p-Si/TiO2作为氧化物基光阳极，氧化物基光电阴极和共价光电阴极的模型系统，以建立对光电极/TiO2界面的整体理解。该团队将改变TiO2层的结晶度、厚度和沉积方法以及半导体电极的表面（组成和原子排列），系统地改变界面，并全面研究它们对光电极整体性能的影响。该项目有可能为制备不同类型光电极的最佳TiO2保护层提供急需的合理指导，从而最大限度地提高太阳能到燃料的转换效率和各种光电极的稳定性。除此之外，该项目还将提供结合实验和计算研究的策略，以研究金属氧化物之间或金属氧化物与非氧化物半导体之间形成的复杂界面。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

With the support of the Chemical Catalysis program in the Division of Chemistry, Professor Kyoung-Shin Choi of the University of Wisconsin-Madison and Professor Giulia Galli of the University of Chicago are studying semiconductor electrodes that can utilize solar energy to split water and produce hydrogen gas, a clean fuel. These semiconductor electrodes are called photoelectrodes, and they often need to be coated by a protection layer to enhance their performance and stability. To date, titanium dioxide (TiO2) has been the most extensively used material as a protection layer due to its inertness. However, the optimal characteristics of an effective TiO2 protection layer reported in the literature are inconsistent. Using combined experimental and computational approaches, Choi and Galli will work toward obtaining a microscopic understanding of how different photoelectrode-TiO2 interfaces influence overall photoelectrode performance. The teams aims to elucidate the photoelectrode-dependent characteristics of the TiO2 layer to optimally protect different types of photoelectrodes. This project is aimed at enabling the rational design of optimal photoelectrode/TiO2 assemblies for efficient and sustainable solar water splitting. In terms of broader impact, Choi and Galli will maintain a website that contains validated sets of data, which will be easily accessible and reusable by members of the community. This website will enhance the infrastructure for guiding researchers to study solar water splitting and other complex systems using combined experimental and computational approaches. This project will also train graduate students in a highly interdisciplinary environment and generate versatile researchers in the field of clean fuel production using renewable solar energy.Under this award, the Choi (U Wisconsin)/ Galli (U Chicago) team will study photoelectrodes that can utilize solar energy to split water and produce hydrogen gas, a clean fuel. . Choi and Galli will use tightly integrated experimental and computational investigations with the goal of achieving a comprehensive understanding of the photoelectrode-dependent characteristics of the TiO2 layer to optimally protect different types of photoelectrodes while maximizing photocurrent and photovoltage generation. The team will elucidate the impact of the photoelectrode/TiO2 interface on band alignments and electron-hole recombination. They will use n-BiVO4/TiO2, p-Cu2O/TiO2, and p-Si/TiO2 as model systems for oxide-based photoanodes, oxide-based photocathodes, and covalent photocathodes, respectively, to build toward a holistic understanding of photoelectrode/TiO2 interfaces. The team will vary the crystallinity, thickness, and deposition method of the TiO2 layer as well as the surface of the semiconductor electrode (composition and atomic arrangement) to systematically alter the interface and comprehensively investigate their impacts on the overall performance of the photoelectrodes. This project has the potential to provide critically needed rational guidelines for the preparation of optimal TiO2 protection layers for different types of photoelectrodes that can maximize the solar-to-fuel conversion efficiency and the stability of various photoelectrodes. Beyond this, the project will also offer strategies to combine experimental and computational investigations to study complex interfaces formed between metal oxides or between metal oxides and non-oxide semiconductors.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.