Increasing the Reductive Stability of Self-Assembled Monolayers on Metallic Surfaces to Enable Reductive Electrocatalysis

密歇根大学安娜堡分校的Charles McCrory和James Penner-Hahn教授在美国国家科学基金会化学部大分子、超分子和纳米化学计划的支持下，研究在电化学操作条件下导致固体表面(自组装单分子膜或SAM)上的有机分子单层膜从表面分离的事件(机制)的顺序。这一过程被称为还原解吸，人们对此知之甚少。对这一过程的更好理解为设计更强大的SAM系统铺平了道路。结合电分析技术、先进的X射线和红外光谱，可以深入了解解吸的机理。坚固的自组装膜对许多实际应用至关重要，包括用于锚定与能源和环境化学相关的反应的催化剂，例如用于太阳能燃料生产的二氧化碳减少和用于废水修复的硝酸盐还原。该项目还提供了一个促进科学素养的平台，通过正规培训学生研究人员与公众沟通，通过互动演示催化和腐蚀概念与当地社区积极接触，以及接待底特律高中生在密歇根大学进行暑期研究实习。使用定义明确的自组装单分子膜(SAM)将分子催化剂固定在电极表面，便于进行新催化剂开发所需的仔细的机械、动力学和光谱电化学研究。然而，由于硫醇基自组装膜在金和其他金属表面上的还原不稳定性，限制了将自组装膜用于将电催化剂与电极表面连接起来进行具有社会意义的反应，如二氧化碳还原和硝酸盐还原。将分子催化剂直接固定到金属表面的还原稳定自组装膜的发现是分子电催化领域的一项使能技术，它可能有助于对已知的和正在出现的电催化剂进行仔细和完整的机理和动力学分析。目前，缺乏对还原解吸过程的机械理解，限制了新的、更还原稳定的系统的合理设计。该项目结合了电分析技术和先进的X射线和红外光谱，探索了还原脱附过程中自组装单分子膜的电子和物理结构，为还原脱附的机理提供了见解。这些机制研究的结果可能有助于合理设计新的、更还原稳定的自组装膜，使其能够固定化和原位光谱电化学研究对能源和环境化学重要的多电子转换电催化剂。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

Professors Charles McCrory and James Penner-Hahn of the University of Michigan-Ann Arbor are supported by the Macromolecular, Supramolecular, and Nanochemistry Program of the NSF Division of Chemistry to study the sequence of events (mechanisms) that cause single layer films of organic molecules on solid surfaces (self-assembled monolayers, or SAMs) to detach from the surface under electrochemical operating conditions. The process, which is called reductive desorption, is poorly understood. A better understanding of the process paves the way for the design of more robust SAM systems. A combination of electroanalytical techniques, advanced X-ray and IR spectroscopies are used to provide insight into the mechanism of desorption. Robust SAMs are critical for many practical applications, including their use to anchor catalysts for reactions relevant to energy and environmental chemistry, such as carbon dioxide reduction for solar fuels generation and nitrate reduction for wastewater remediation. This project also provides a platform to promote scientific literacy through formal training of student researchers in communicating to the general public, active engagement with the local community through interactive demonstrations of the concepts of catalysis and corrosion, and hosting Detroit high school students in summer research internships at the University of Michigan.The use of well-defined self-assembled monolayers (SAMs) to tether molecular catalysts to electrode surfaces facilitates the careful mechanistic, kinetic, and spectroelectrochemical studies needed for new catalyst development. However, the use of SAMs for tethering electrocatalysts to electrode surfaces for reactions of societal importance, such as carbon dioxide reduction and nitrate reduction, is limited by the reductive instability of thiol-based SAMs on gold and other metal surfaces. The discovery of reductively-stable SAMs for the direct immobilization of molecular catalysts to metallic surfaces is an enabling technology in molecular electrocatalysis that may facilitate careful and complete mechanistic and kinetic analysis of known and emerging electrocatalysts. Currently, a lack of mechanistic understanding of the reductive desorption process limits the rational design of new, more-reductively stable systems. This project uses a combination of electroanalytical techniques and advanced X-ray and infrared spectroscopies to probe the electronic and physical structures of self-assembled monolayers during the reductive desorption process, providing insights into the mechanism of reductive desorption. The results of these mechanistic studies may facilitate the rational design of new, more reductively-stable SAMs that enable the immobilization and in situ spectroelectrochemical study of electrocatalysts for multi-electron transformations important to energy and environmental chemistry.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.