Prado Desiree Mae, Gonzaga Aaron Niño, Carter Brady, Burda Clemens
Department of Chemistry, Case Western Reserve University, Cleveland, OH, 44106, USA.
Novasina AG, 2810 S UT-66, Morgan, UT, 84050, USA.
Chemistry. 2025 Apr;31(24):e202500717. doi: 10.1002/chem.202500717. Epub 2025 Mar 30.
The presence of water in nonaqueous deep eutectic solvent (DES) electrolytes has been debated in recent years, with efforts ranging from its complete removal to willful addition. It was shown that controlled amounts of water can be beneficial, as it not only enhances the physicochemical properties of these electrolytes but also has no significant detrimental effects on their electrochemical stability. Despite these advantages, there is still limited understanding of how water interacts with DES systems at the molecular level. This study examines the water activity in ethylene glycol and glycerol, as well as their binary mixtures with choline chloride to form the DESs ethaline and glyceline, respectively. In this work, we show that the high electrochemical stability of glyceline is related to its lower water activity compared to ethaline and can be attributed to the robust H-bonding network formed by the three hydroxyl groups of glycerol. Its 3D H-bond network effectively integrates water molecules within its solvent structure, reducing degradation and maintaining stability at higher water contents. The deviations from the ideal Raoult's law behavior are reflected in the water activity and activity coefficients, which highlight the intricate H-bond interactions within DES-water mixtures. Water acts like a lubricant within the more viscous DES mixtures without being detrimental to their electrochemical performance. The presented results emphasize the necessity of customizing DES-water compositions to enhance their performance as electrolytes, especially in flow battery applications where electrochemical stability, ionic conductivity, and fluidity are of utmost importance.
近年来，非水型深共熔溶剂（DES）电解质中水分的存在一直存在争议，人们采取了从完全去除到有意添加等各种措施。研究表明，控制适量的水可能有益，因为它不仅能增强这些电解质的物理化学性质，而且对其电化学稳定性没有显著的不利影响。尽管有这些优点，但在分子水平上，人们对水与DES体系如何相互作用的了解仍然有限。本研究考察了乙二醇和甘油中的水活度，以及它们与氯化胆碱形成DESs（分别为乙盐和甘油盐）的二元混合物中的水活度。在这项工作中，我们表明，与乙盐相比，甘油盐的高电化学稳定性与其较低的水活度有关，这可归因于甘油的三个羟基形成的强大氢键网络。其三维氢键网络有效地将水分子整合到其溶剂结构中，减少降解并在较高水含量下保持稳定性。与理想拉乌尔定律行为的偏差反映在水活度和活度系数中，这突出了DES-水混合物中复杂的氢键相互作用。在更粘稠的DES混合物中，水起到了润滑剂的作用，而不会对其电化学性能产生不利影响。给出的结果强调了定制DES-水组合物以提高其作为电解质性能的必要性，特别是在液流电池应用中，电化学稳定性、离子导电性和流动性至关重要。
