Collaborative Research: Ion Mobility in Aqueous Acids, Bases, and Salts

在化学系化学结构、动力学和机理a （CSDM-A）项目的支持下，由圣母大学的Steven Corcelli教授和宾夕法尼亚州立大学的Paul Cremer教授领导的一个研究小组正在用一种完全集成的实验和理论建模方法研究离子在水中的迁移性。含盐溶液（包括酸和碱）在许多化学、生物和环境过程中都是必不可少的，而离子传输速率与采用水性电解质的新兴电池技术尤其相关。然而，离子运输的详细分子机制，包括反离子和离子配对的作用，尚不完全清楚。因此，本项目的研究目标是在分子水平上探索水中离子的迁移，以统一理解反离子和离子对在水溶液酸、碱和盐中离子迁移的结构、动力学和机制中的作用。除了这项工作的更广泛的科学影响外，该项目还包括为研究生和本科生提供高级培训机会，以及为高中生开发相关的实验室实验。初步发现，反离子对氢氧化物迁移率有很大影响，这表明离子配对效应是酸、碱和盐迁移率的核心。本项目系统研究了Hofmeister系列离子在酸、碱和盐溶液中的浓度函数。实验上，通过电化学阻抗谱测量了扩散常数，并结合拉曼光谱和红外光谱阐明了离子结构、水合作用和质子离域的信息。互补的核磁共振波谱测量产生质子转移率和有关单个离子迁移率的信息。理论上，酸和碱用从头算分子动力学模拟，盐用分子动力学模拟。基于模拟的计算提供了各自离子对之间的自由缔合能，并有助于解释实验拉曼和红外光谱。光谱和模拟研究协同结合，提供了分子水平上对扩散常数测量的理解。联合研究阐明了反离子对质子跳跃Grotthuss机制的影响，以及水溶液中溶剂共享离子对与接触离子对的特殊作用。这项工作的广泛影响包括更好地理解离子迁移对许多技术应用的重要性，高级学生培训机会，以及探索疏水界面离子配对的高中实验室实验的开发和实施。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 support from the Chemical Structure, Dynamics, and Mechanisms-A (CSDM-A) Program in the Division of Chemistry, a research team led by Professors Steven Corcelli at the University of Notre Dame and Paul Cremer at Pennsylvania State University is investigating the mobility of ions in water with a fully integrated experimental and theoretical modeling approach. Solutions containing salt, including acids and bases, are essential in many chemical, biological, and environmental processes, and the rates of ion transport are especially relevant to emerging battery technologies employing aqueous electrolytes. However, the detailed molecular mechanism for ion transport, including the role of counterions and ion-pairing, is not fully understood. Thus, the research objective of this project is to explore ionic mobility in water at the molecular level to achieve a unified understanding of the role of counterions and ion-pairing on the structure, dynamics, and mechanisms of ion transport in aqueous acids, bases, and salts. In addition to the broader scientific impacts of the work, the project also includes advanced training opportunities for graduate and undergraduate students, as well as the development of a related laboratory experiment for high school students. Preliminary findings that counterions substantially impact hydroxide mobility suggest that ion-pairing effects are central to acid, base, and salt mobility. This project involves a systematic study of Hofmeister series ions in acid, base, and salt solutions as a function of concentration. Experimentally, diffusion constants are measured by electrochemical impedance spectroscopy, and a combination of Raman and infrared spectroscopy elucidate information about ion structure, hydration, and proton delocalization. Complementary nuclear magnetic resonance spectroscopy measurements yield proton transfer rates and information about the mobility of individual ions. Theoretically, the acids and bases are simulated with ab initio molecular dynamics and the salts with molecular dynamics. Calculations based on the simulations provide the free energy of association between respective ion pairs and aid the interpretation of the experimental Raman and infrared spectra. The spectroscopic and simulation studies synergistically combine to provide a molecular-level understanding of diffusion constant measurements. The combined studies elucidate the impact of counterions on the Grotthuss mechanism of proton hopping and the particular roles of solvent-shared versus contact ion-pairing in aqueous electrolyte solutions. The broader impacts of the work include the importance of better understanding ion mobility for many technological applications, advanced student training opportunities, and development and implementation of a high school laboratory experiment that explores ion-pairing at hydrophobic interfaces.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.