Non-situ Investigations of Surface Chemistry in a Model Electric Double Layer

CBET-0828765 Medlin燃料电池和其他应用开发更好的电催化剂的主要挑战是提高对电化学界面处表面反应机理的理解。虽然在描述金属-真空界面的表面反应性方面已经取得了很大进展，但金属电极上的催化反应通常是以极化的金属-电解液界面为特征的。部分由于这种界面的复杂性，很少有人致力于模拟双电层(EDL)环境对表面反应性的影响。在这项工作中，将详细研究EDL的两个重要方面对表面过程的影响。首先，将表征溶剂-吸附相互作用在改变表面反应路径中的作用。其次，将研究近表面电场对这些反应的影响，以确定吸附偶极与界面电场的相互作用如何影响反应机理。这些研究将使用所谓的非原位方法进行，在这种方法中，EDL的影响将在超高真空中对单晶进行模拟，其中可能会使用强大的光谱技术来详细表征表面中间体。这种方法并不是为了提供高精度的电催化剂工作模拟而设计的。相反，目标是确定EDL环境影响表面反应的基本机制。程序升温脱附(TPD)、高分辨电子能量损失谱(HREELS)和功函数测量等方法将被用来表征被研究的表面，而密度泛函方法将被用于所需的理论研究。为了研究溶剂化的影响，在被吸附物质覆盖的表面上添加控制量的水和其他溶剂，并进行不同的热处理。界面极化的研究将主要通过吸附强电子给体，特别是碱金属，以及表面吸附来进行。溶剂化和极化的影响将被探索的几个关键过程，如氧的吸附和解离，质子的形成，和质子转移。由于这项研究涉及对许多电催化过程至关重要的表面过程的基础研究，因此它在跨学科中产生广泛影响的潜力是巨大的。例如，能够解释溶剂化环境和电极电位的趋势对于改进的电催化剂的第一性原理开发是重要的。拟议的工作部分是出于初步的理论研究，这项工作的另一个目标是提供实验光谱信息，以帮助验证正在进行的和未来的理论建模工作。拟议的研究还将深入了解在酸性介质中进行的反应的重要机制，包括与生物炼油转化有关的机制，以及在存在电场的情况下进行的表面过程。PI将与全国黑人工程师协会(NSBE)和西班牙裔专业工程师协会(SHPE)合作，招聘本科生研究人员助理，以促进能源教育的多样性努力。还计划向当地一所高中开展外联工作，重点是宣传学生影响可再生能源研究的能力。

CBET-0828765MedlinA major challenge for development of better electrocatalysts for fuel cell and other applications is improving the understanding of surface reaction mechanisms at electrochemical interfaces. Whereas major strides have been made in describing surface reactivity at a metal-vacuum interface, catalytic reactions on metal electrodes are typically characterized by a polarized metal-electrolyte interface. In part because of the complexity of this interface, little study has been devoted to modeling the influence of the electric double layer (EDL) environment on surface reactivity. In this work, the effects of two important facets of the EDL on surface processes will be studied in detail. First, the role of solvent-adsorbate interactions in altering surface reaction pathways will be characterized. Second, the influence of near-surface electric fields on those same reactions will be investigated to determine how interactions of adsorbate dipoles with interfacial electric fields can affect reaction mechanisms. The proposed studies will be carried out using a so-called non-situ approach, in which effects of the EDL will be modeled on single crystals in ultrahigh vacuum, where powerful spectroscopic techniques may be employed to characterize surface intermediates in detail. This approach is not designed to provide a highly accurate simulation of a working electrocatalyst. Instead, the goal is to identify the fundamental mechanisms by which the EDL environment affects surface reactions. Temperature programmed desorption (TPD), high resolution electron energy loss spectroscopy (HREELS), and work function measurements, among other methods, will be employed to characterize the surfaces under study, and density functional methods will be used for the required theoretical studies. To investigate the effects of solvation, controlled amounts of water and other solvents will be added above an adsorbate-covered surface and subjected to various thermal treatments. The interface polarization studies will largely be conducted by adsorbing strong electron donors, especially alkali metals, together with surface adsorbates. The effects of solvation and polarization will be probed for several key processes, such as oxygen adsorption and dissociation, proton formation, and proton transfer. Because this research deals with a fundamental study of surface processes essential for many electrocatalytic processes, its potential for broad impact across disciplines is great. For example, the ability to account for trends in solvation environment and electrode potential is important for first-principles development of improved electrocatalysts. The proposed work is partly motivated by preliminary theoretical studies, and an additional objective of this work is to provide experimental spectroscopic information to help validate ongoing and future theoretical modeling efforts. The proposed studies will also provide insights into mechanisms important for reactions conducted in acidic media, including those associated with biorefinery conversions, and surface processes conducted in the presence of electric fields. The PI will work with the National Society of Black Engineers (NSBE) and the Society of Hispanic Professional Engineers (SHPE) to recruit undergraduate researcher assistants to promote diversity efforts in energy education. Outreach efforts to a local area high school focused on communicating the ability of students to impact renewable energy research are also planned.