Ionic Charge Transport and Molecular Reorientation in Deep Eutectic Solvents studied by Dielectric Spectroscopy and Nuclear Magnetic Resonance

电解质是能量储存和转换装置如电池、燃料电池或超级电容器的基本组分。太阳能和风能的不连续可用性以及电动汽车的未来成功需要显着推进这些技术。因此，寻找更好的电解质是确保未来可持续能源供应的关键。一类有前途的新型电解质是深共熔溶剂（DES），与其他材料相比，其在易于制备、低成本、可持续性和生物相容性方面具有上级优势。DES通常由盐和分子氢键供体组成。两种组分的混合产生典型的共晶熔点降低，使DES在室温下为液体。这可以将盐转化为液体电解质，否则在室温下是结晶的。如对于低共熔混合物经常发现的，当足够快地冷却时，DES倾向于表现出玻璃化转变。了解DES中的离子传输机制是促进其在电化学应用方面优化的重要目标。在本项目中，将使用介电谱（DS）和核磁共振（NMR）研究DES的离子电荷传输和玻璃形成性能，并辅以流变学和量热测量。DS对离子的平移位移以及偶极分子的重定向运动敏感，其中两种动力学可以耦合。NMR能够通过采用合适的核探针和同位素异构体以混合伴侣特异性方式检测两种动力学。因此，NMR理想地补充DS，其覆盖异常宽的动态范围，但不提供这样的选择性信息。此外，这些方法的组合也是理想的调查玻璃化冻结的离子和分子动力学，因为它们可以提供有关这些动态的玻璃化transition.It的过程中的连续减慢的详细信息是本项目的目标，以实现更好地理解的微观机制，支配在DES的离子电荷传输。特别是，我们希望探索到目前为止，往往被忽视的重定向运动在这些材料和平移离子动力学的相关性。在其他类型的离子导体中，分子重新取向被认为是通过旋转门机制打开离子电荷传输的途径。我们的目的是澄清这是否也可以发挥作用的DES。此外，我们计划研究的唯一稀疏调查的玻璃化转变和玻璃化性质的DES详细。特别是，它需要澄清的玻璃化温度和典型的非Arrhenius玻璃动力学影响离子电荷输运在DES。

Electrolytes are essential components of energy-storage and -conversion devices such as batteries, fuel cells or supercapacitors. The non-continuous availability of solar and wind energy and a future success of electromobility require to advance these technologies significantly. Finding better electrolytes, thus, is key to ensuring tomorrow's sustainable energy supply. A promising new class of electrolytes are deep eutectic solvents (DESs), which are superior compared to other materials concerning ease of preparation, low cost, sustainability and biocompatibility. DESs are commonly composed of a salt and a molecular hydrogen-bond donor. The mixing of the two components generates the typical eutectic melting-point reduction, rendering DESs liquid at room temperature. This can transform salts, that otherwise are crystalline at room temperature, to liquid electrolytes. As often found for eutectic mixtures, DESs tend to exhibit a glass transition when cooled sufficiently fast. To understand the ionic transport mechanism in DESs is an important goal to facilitate their optimization with respect to electrochemical applications.Within the present project, the ionic charge-transport and glass-forming properties of DESs shall be investigated using dielectric spectroscopy (DS) and nuclear magnetic resonance (NMR), supplemented by rheological and calorimetric measurements. DS is sensitive to the translational displacements of the ions as well as to the reorientational motions of the dipolar molecules, where the two dynamics can be coupled. NMR is able to detect both dynamics in a mixing-partner-specific manner by employing suitable nuclear probes and isotopomers. Thus, NMR ideally complements DS, which covers an exceptionally broad dynamic range but does not provide such selective information. Moreover, the combination of these methods is also ideal to investigate the glassy freezing of the ionic and molecular dynamics as they can provide detailed information concerning the continuous slowing down of these dynamics in the course of the glass transition.It is the goal of the present project to achieve a better understanding of the microscopic mechanisms that govern the ionic charge transport in DESs. Especially, we wish to explore the so-far often neglected reorientational motion in these materials and its relevance for the translational ion dynamics. In other classes of ionic conductors, the molecular reorientation was, suggested to open pathways for the ionic charge transport via a revolving-door-like mechanism. We aim at clarifying whether this may also play a role for DESs. Moreover, we plan to study the only sparsely investigated glass transition and the glassy properties of DESs in detail. Especially, it needs to be clarified how the glass temperature and the typical non-Arrhenian glassy dynamics affect the ionic charge transport in DESs.