Molecular Physics of the Electrical Double Layers in Ionic Liquids

离子液体是一类新型电解质，具有许多潜在的高冲击性能，如宽电化学窗口、低蒸气压和优异的热稳定性。这些特性在电化学应用中提供了明显的优势，如太阳能电池和超级电容器。 在这些潜在的应用中，电极和离子液体界面处的双电层（EDLs）在决定系统性能方面起着关键作用。然而，对这些EDLs的知识是非常有限的：许多基本问题，如电容电位相关性和超小纳米孔中的EDLs的电容目前知之甚少。这种有限的理解使得使用离子液体作为电解质的电化学系统的设计和优化变得困难，从而阻止了离子液体的潜力被充分利用。因此，提高我们对离子液体中EDLs的理解是至关重要的。 本研究的目的是利用分子动力学模拟研究离子液体中的双电层。具体而言，PI将首先研究离子液体和平面电极界面处的EDLs，以描述电极和离子的电/物理化学性质如何影响其结构和电容。在离子液体填充的亚纳米孔中的EDLs将被研究以阐明纳米限制和表面曲率对这些孔中的EDLs的结构和电容的协同效应。智力优点：在平面EDLs的研究中，离子液体中的EDLs的新图片，即，离子-离子和离子-电极相关性在决定双电层结构中起着关键作用。这幅图代表了流行的EDL模型的范式转变，并得到了令人信服的初步数据的支持。在这个新理念的指导下，PI？fs模拟设计和数据分析明显不同于那些在以前的研究，预计会导致新的见解的依赖性的EDL结构的离子的性质和电极的极化/化学。有了这个，PI将阐明不同电容的机制？]在先前的实验中观察到的EDL的潜在关系和令人惊讶的离子特异性，这违背了现有的EDL模型。在亚纳米孔中的双电层的研究中，通过在具有精确定义的几何形状的孔中进行模拟，并通过同时计算双电层的微观结构和电容，PI的小组将首次自洽地测试关于限制和表面曲率对亚纳米孔中双电层电容的影响的先验假设，并阐明测试结果的潜在机制。总之，这些研究将极大地推进对离子液体中EDLs的基本理解，并朝着建立使用离子液体作为工作电解质的电化学系统的合理设计的知识基础迈出坚实的一步。更广泛的影响：该项目将与克莱姆森大学的教育活动密切相关。参加这个项目的学生将接触到不同的领域，如物理化学，原子建模和计算方法。本科生将通过PI家庭部门的荣誉研究计划参与研究。 各种资源，例如，克莱姆森大学的少数族裔招生计划将被用来从代表性不足的群体中招收学生参加这个项目。研究结果将被制作成海报/电影，向K-12学生介绍电能存储。将通过期刊出版物和在专业会议上的介绍传播研究成果。将开发和维护一个网站，重点介绍离子液体中EDLs的基本物理学及其在电化学系统中的作用。将通过正式和非正式渠道向目标受众宣传该网站。

0967175QiaoIonic liquids are a new class of electrolytes with many potentially high impact properties such as wide electrochemical windows, low vapor pressure, and excellent thermal stability. These properties offer distinct advantages in electrochemical applications such as solar cells and supercapacitors. In these potential applications, the electrical double layers (EDLs) at the interfaces of electrodes and ionic liquids play a critical role in determining the system performance. However, the knowledge on these EDLs is very limited: many fundamental issues such as the capacitance potential correlation and the capacitance of EDLs in ultrasmall nanopores are poorly understood at present. Such a limited understanding renders the design and optimization of electro-chemical systems using ionic liquids as electrolyte difficult, and thus prevents the potential of ionic liquids from being fully exploited. Therefore, it is critical to improve our understanding of the EDLs in ionic liquids. The objective of this research is to investigate the electrical double layers (EDLs) in ionic liquids using molecular dynamics simulations. Specifically, the PI will first study the EDLs at the interfaces of ionic liquids and planar electrodes to delineate how their structure and capacitance are affectedby the electrical/physicochemical properties of electrodes and ions. The EDLs in ionic liquids-filled sub-nanometer pores will then be studied to elucidate the synergistic effects of nano-confinement and surface curvature on the structure and capacitance of EDLs in these pores.Intellectual Merit: In the study of planar EDLs, a new picture for the EDLs in ionic liquids, i.e., the Ion-ion and ion-electrode correlations play a key role in determining the EDL structure, is proposed. This picture represents a paradigm shift from the prevalent EDL models, and is supported by compelling preliminary data. Guided by this new idea, the PI?fs simulation design and data analysis differ distinctly from those in prior research and are expected to lead to new insights into the dependence of EDL structure on the nature of ions and on the polarization/chemistry of electrodes. With this, the PI will elucidate the mechanism of the diverse capacitance?]potential relations and surprising ion specificity of EDL observed in previous experiments, which defy existing EDL models. In the study of EDLs in sub-nanometer pores, by doing simulations in pores with precisely defined geometry and by simultaneously computing the microstructure and capacitance of the EDLs, the PI's group will, for the first time, self-consistently test the prior hypotheses on effects of confinement and surface curvature on EDL capacitance in sub-nanometer pores, and elucidate the underlying mechanisms of the test result. Together, these researches will greatly advance the fundamental understanding of the EDLs in ionic liquids and make a firm step towards building the knowledge base for the rational design of electrochemical systems using ionic liquids as working electrolytes.Broader Impacts: The project will be tied intimately with the educational activities at Clemson University. Students participating in this project will be exposed to diverse fields such as physical chemistry, atomistic modeling and computational methods. Undergraduate students will be involved in the research through the Honors Research Program in the PI's home department. Various resources, e.g., the minority recruitment programs at Clemson University, will be utilized to recruit students from underrepresented groups to participate in this project. Research results will be developed into posters/movies to introduce electrical energy storage to K-12 students. Research will be disseminated through journal publications and presentations in professional conferences. A website centering on the fundamental physics of the EDLs in ionic liquids and their role in electrochemical systems will be developed and maintained. The website will be advertised to the target audience via formal and informal channels.