Electrocatalytic Studies at Single, Structurally Well-defined Nanoparticles

德克萨斯大学奥斯汀分校的Richard M. Crooks和Graeme Henkelman教授得到化学学部化学催化项目的支持，从事催化材料的基础研究。该项目旨在更好地了解纳米级电催化剂。历史上开发新催化剂的方法是基于爱迪生的方法，即使用科学直觉，然后进行试验和错误测试。然而，随着功能强大的计算机的出现，使用复杂的计算来设计催化剂已经成为可能。因此，本研究项目的主要科学目标是通过实验测试这种方法在催化剂设计中的有效性。为了实现这一目标，首先合成了单独的、定义良好的纳米颗粒，对其结构进行了表征，并对其电催化性能进行了评估。这开启了一种实验-理论的迭代关系，旨在完善理论工具，使它们最终足够复杂，可用于从第一原理设计更有效的电催化剂。电催化剂对于将化学燃料（如氢）转化为能量，以及能量转化为燃料并以燃料形式储存的一系列相反的反应都很重要。随着人们对国家能源未来的安全性和可持续性的日益关注，以及几种关键催化材料的稀缺性，高效设计更容易获得和有效的电催化剂比以往任何时候都更加重要。在进行这项研究的过程中，学生将获得必要的技术知识，为清洁能源的未来做出贡献，并掌握必要的沟通技巧，向公民和国家政治领导层传达能源相关科学的重要性。该项目的中心目标是合成、表征和评估单个纳米颗粒（NPs）的电催化性能，然后将它们的性质与使用第一性原理理论计算的性质联系起来。为实现这一目标，确定了三个具体目标。具体目标1始于发现将单个铂纳米粒子（PtNPs）的电合成控制在单个纳米级碳电极尖端的方法。这些材料的详细表面结构表征是用电子显微镜、纳米光束衍射和扫描隧道显微镜确定的。利用第一性原理理论，这些结构信息被用来预测这些材料对一氧化碳（CO）和甲酸氧化的电催化效率。选择CO氧化作为研究对象，是因为它是文献中报道的最简单的电化学反应之一，并且已经观察到NP结构对电催化活性的明显影响。它也经常在有机燃料的电催化氧化反应中作为中间产物或副产物形成。理论方法包括为这些反应定义特定的描述符。最初，这些描述符将通过假设反应机制，然后计算反应中间体的结合能来确定。由此产生的理论预测然后进行实验验证。具体目标2通过扩展可实现的表面结构库来推进上述方法，这反过来又提供了更严格的理论测试。最后，在具体目标3中，该项目的范围进一步扩展到包括其他单np系统，包括金np和单原子合金np。在这部分项目中，理论指导电催化反应的选择和测试材料的组合。这一目的的目的是证明方法的范围，并进一步挑战理论的预测可靠性。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。

Professors Richard M. Crooks and Graeme Henkelman of the University of Texas at Austin are supported by the Chemical Catalysis Program of the Division of Chemistry to undertake fundamental studies of catalytic materials. The project is aimed at developing a better understanding of nanometer-scale electrocatalysts. The historical approach for developing new catalysts is based on the Edisonian method of using scientific intuition followed by trial-and error-testing. With the advent of very powerful computers, however, it has become possible to imagine designing catalysts using sophisticated calculations. Accordingly, the main scientific goal of the present research project is to experimentally test the validity of this approach to catalyst design. To accomplish this goal, individual, well-defined nanoparticles are first synthesized, structurally characterized and their electrocatalytic properties evaluated. This initiates an experimental-theoretical iterative relationship intended to refine theoretical tools to the point that they will eventually be sufficiently sophisticated to be used to design more effective electrocatalysts from first principles. Electrocatalysts are important for converting chemical fuels, like hydrogen, into energy, and also for the opposite family of reactions in which energy is converted to and stored in the form of fuels. With rising concerns over the security and sustainability of the nation's energy future, and the scarcity of several key catalytic materials, it is more important than ever to efficiently design more accessible and effective electrocatalysts. During the course of conducting this research, students are provided with the technical knowledge necessary to contribute toward a clean-energy future and the communication skills necessary to convey the importance of energy-related science to citizens and the nation's political leadership. The central objective of this project is to synthesize, characterize, and evaluate the electrocatalytic performance of individual nanoparticles (NPs), and then correlate their properties to those calculated using first-principles theory. To address this objective, three specific aims are identified. Specific aim 1 commences with the discovery of methods for controlling the electrosynthesis of single platinum NPs (PtNPs) onto the tips of individual, nanometer-scale carbon electrodes. Detailed surface structural characterization of these materials is determined using electron microscopy, nanobeam diffraction, and scanning tunneling microscopy. This structural information is used to predict, using first-principles theory, the electrocatalytic efficiency of these materials for carbon monoxide (CO) and formic acid oxidation. CO oxidation is selected for study because it is one of the simplest electrochemical reactions reported in literature in which clear effects of NP structure on electrocatalytic activities have been observed. It also often forms as an intermediate or by-product in electrocatalytic oxidation reactions of organic fuels. The theoretical approach involves defining particular descriptors for these reactions. Initially, these descriptors will be determined by postulating reaction mechanisms and then calculating binding energies of reaction intermediates. The resulting theoretical predictions are then experimentally tested. Specific aim 2 advances the foregoing methodology by expanding the library of achievable surface structures, which in turn provides a more rigorous test of theory. Finally, in specific aim 3, the scope of the project expands further to include other single-NP systems, including gold NPs and single-atom alloyed NPs. In this part of the project, theory guides the choice of electrocatalytic reactions and the combinations of materials tested. The goal of this aim is to demonstrate the scope of the methodology and to further challenge the predictive reliability of theory.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.