Controlling Charges on Oxide Surfaces for Enhanced Photochemical Reactivity

非技术描述：经济上可行的利用光从水中分离氢燃料仍然是科学界的一个重要技术目标。氢是一种有价值的燃料，因为它的能量密度高，燃烧时不会产生温室气体。限制水裂解制氢效率的一个因素是现有催化剂的性能。催化剂表面要想分解水，必须完成两个功能：它必须将带负电的电子和带正电的空穴传递给表面的水分子。无论哪一种作用发生得较慢，都会限制整个反应。在这个项目中，创造了具有两种不同表面的催化剂。表面的一些区域促进负电荷的转移，而另一些区域促进正电荷的转移。调整相关区域以优化整体反应速率。该方法为设计经济的太阳能制氢水裂解催化剂提供了有价值的工具。该项目将通过以下途径产生更广泛的影响：培训本科生和研究生、基于网络的教育应用和纳入可持续发展课程、将研究成果传播到校园以外、扩大特别是妇女参与工程/科学。技术细节：这个项目是基于这样一个假设，即氧化物表面的还原（正）域和氧化（负）域的相对面积是可以控制的，并且这个比例影响可用于生产太阳能燃料或降解环境污染物的催化剂的整体光化学反应速率。采用可控气氛高温退火来定制表面终止。表面电荷分布是通过扫描电位显微镜测量的，并使用光还原和氧化反应来评估，这些反应在反应部位留下不溶性产物。这个项目的新颖性和优点在于努力控制终止化学，并将极性域的类型和相关区域与表面的化学性质联系起来。由于带相反电荷的表面平台分别促进了还原和氧化半反应，具有相反电荷域组合的表面提供了一个近乎理想的环境，在这个环境中，光生成的载流子被分离，反应产物被分离，两个反应的相对速率由带电荷域的相对面积控制。这些因素中的每一个都通过减轻与重组、反反应和两个半反应中反应位点数量不平衡相关的损失来提高光催化效率。该项目展示了如何控制极性表面域，并为实际生产太阳能氢创造更有效的光催化剂。

NON-TECHNICAL DESCRIPTION: The economically feasible separation of hydrogen fuel from water using light remains an important technical goal for the scientific community. Hydrogen is a valuable fuel because it has a high energy density and its combustion does not generate greenhouse gases. One factor that limits efficient hydrogen synthesis by water splitting is the performance of the available catalysts. For the surface of the catalyst to split water, it must perform two functions: it must transfer both negatively-charged electrons and positively-charged holes to water molecules on the surface. Whichever of these functions occurs more slowly limits the overall reaction. In this project, catalysts are created that have two different types of surfaces. Some areas of the surface promote the transfer of negative charge and the other areas promote the transfer of positive charge. The relative areas are adjusted to optimize the overall reaction rate. This approach provides a valuable tool for the design of water splitting catalysts for economic solar hydrogen production. The project will have broader impact through the training of undergraduate and graduate students, web-based applications for education and integration into a course on sustainability, the dissemination of the research results beyond the campus, and broadening participation, particularly of women in engineering/science.TECHNICAL DETAILS: This project is based on the hypothesis that the relative areas of reducing (positive) and oxidizing (negative) domains on an oxide surface can be controlled and that this ratio influences the overall photochemical reaction rate of catalysts that can be used to produce solar fuel or degrade environmental pollutants. Controlled-atmosphere high-temperature annealing is used to tailor the surface termination. The surface charge distribution is measured by scanning potential microscopy and evaluated using photo-reduction and oxidation reactions that leave insoluble products at the site of the reaction. The novelty and merit of this project lie in the efforts to control the termination chemistry and correlate the types and relative areas of polar domains to the chemical properties of the surface. Because oppositely charged surface terraces promote separately the reduction and oxidation half reactions, surfaces with a combination of oppositely charged domains provide a nearly ideal environment where photo-generated charge carriers are separated, reaction products are separated, and the relative rates of the two reactions are controlled by the relative areas of the charged domains. Each of these factors improves photocatalytic efficiency by mitigating losses associated with recombination, back reaction, and an imbalance in the number of reactive sites for the two half reactions. This project demonstrates how to control polar surface domains and create more efficient photocatalysts needed for the practical production of solar hydrogen.