Voltage-dependent interfacial structure and properties of room temperature ionic liquids: operando X-ray studies

西北大学的Pulak Dutta教授在化学学部化学结构动力学和机理（CSDM-A）项目资助下，利用同步辐射源的x射线研究纯分子离子组成的液体（称为室温离子液体，简称RTILs）。这些新型液体已被提出用于各种应用，如电池和超级电容器中的电解质、溶剂等，它们具有许多与更常见的水基液体电解质截然不同的特性。通过研究离子在施加可变电压时如何在电极附近排列，以及这些排列如何随时间发展和变化，研究了这些不寻常性质的纳米级起源。这些研究将发展必要的知识，不仅了解rtil的观察属性，而且最终设计和控制这些行为。这将有可能改进电池和电容器，在微流体系统中操作小液滴的简单方法等。本项目重点研究室温离子液体（RTILs），这是一种带有分子阴离子和/或分子阳离子的熔盐，目的是通过实验研究电极界面附近RTIL离子的静态和动态排列如何响应电场；将这种行为与RTIL中存在的离子的分子结构联系起来；并试图了解结构如何决定或影响观察到的电化学和电润湿性能。主要实验探针是固体rtil界面的原位x射线反射率和掠入射x射线衍射，使用国家同步加速器设施。目前正在研究界面结构及其动力学对离子存在、电极表面性质以及施加的直接电压和交流电压的依赖性，并将其与现有的理论预测进行比较。预期的结果是对RTILs的纳米级界面行为有更好的基本理解，从而提高如何选择或设计离子液体的知识，以优化实际应用所需的性能。

In this project funded by the Chemical Structure Dynamics and Mechanisms (CSDM-A) program of the Chemistry Division, Prof. Pulak Dutta of Northwestern University is using X-rays from synchrotron radiation sources to study liquids composed purely of molecular ions (known as room-temperature ionic liquids, or RTILs). These novel liquids have been proposed for a variety of applications such as electrolytes in batteries and supercapacitors, solvents, etc., and they have a number of properties that are quite different from those of more commonly known water-based liquid electrolytes. The nanoscale origins of these unusual properties are investigated by studying how the ions arrange themselves near electrodes when variable voltages are applied, and how these arrangements develop and change with time. These studies will develop the knowledge necessary to not just understand the observed properties of RTILs, but ultimately to design and control these behaviors. This would potentially allow improved batteries and capacitors, easy ways to manipulate small droplets in microfluidic systems, etc.This project focuses on room-temperature ionic liquids (RTILs), which are molten salts with molecular anions and/or molecular cations The objectives are to study experimentally how the static and dynamic arrangements of RTIL ions near electrode interfaces respond to electric fields; to correlate this behavior with the molecular structures of the ions present in the RTIL; and to seek to understand how the structures determine or affect the observed electrochemical and electrowetting properties. The primary experimental probe is in situ X-ray reflectivity and grazing incidence X-ray diffraction from solid-RTIL interfaces, using national synchrotron facilities. The dependence of the interfacial structure and its dynamics on the ions present, the nature of the electrode surface, and on applied direct and alternating voltages, are being studied and compared to existing theoretical predictions. The anticipated outcome is a better fundamental understanding of the nanoscale interfacial behavior of RTILs, and thus improved knowledge of how to select or design ionic liquids in order to optimize desired properties for practical applications.