Forschungszentrum Jülich GmbH, Institute of Energy and Climate Research - Fundamental Electrochemistry (IEK-9), 52428, Jülich, Germany.
RWTH Aachen University, Institute of Technical and Macromolecular Chemistry, 52062, Aachen, Germany.
Chemphyschem. 2022 Jan 5;23(1):e202100602. doi: 10.1002/cphc.202100602. Epub 2021 Nov 3.
Choline-based electrolytes have been proposed as environmentally friendly and low-cost alternatives for secondary zinc air batteries. Choline acetate [Ch] [OAc] in protic (D O) and aprotic (DMSO-d ) solvents has been studied by means of concentration-dependent H NMR, viscosity, and density measurements. The viscosities have been calculated on the basis of the Jones-Dole equation and showed that the dominant contribution originates from short-range ion-solvent interactions. Site-specific association affinities were assigned from NMR chemical shift titrations. In DMSO-d , the hydroxyl group of choline was found to have the smallest dissociation constant followed by the methyl group of acetate. The corresponding Gibbs energies at low concentration were found to be in agreement with a solvent-separated ion pair (2SIP) configuration, whereas at concentrations above 300 mM, a solvent-shared ion pair (SIP) configuration was assigned. For [Ch] [OAc] in D O, association effects were found to be weaker, attributed to the high dielectric constant of the solvent. On time scales on the order of 100 ms, NMR linewidth perturbations indicated a change in the local rotational dynamics of the ions, attributed to short-range cation-solvent interactions and not to solvent viscosity. At 184 mM, 40 % of the cations in DMSO-d and 10 % in D O were found to exhibit short-range interactions, as indicated by the linewidth perturbations. It was found that at about 300 mM, the ions in DMSO-d exhibit a transition from free to collective translational dynamics on time scales on the order of 400 ms. In DMSO-d , both ions were found to be almost equally solvated, whereas in D O solvation of acetate was stronger, as indicated by the obtained effective hydrodynamic radii. For [Ch] [OAc] in DMSO-d , the results suggest a solvent-shared ion association with weak H-bonding interactions for concentrations between 0.3-1 M. Overall, the extent of ion association in solvents such as DMSO is not expected to significantly limit charge transport and hinder the performance of choline-based electrolytes.
胆碱基电解质已被提议作为替代二次锌空气电池的环保且低成本的选择。在质子（D O ）和非质子（DMSO-d ）溶剂中，通过浓度依赖性 1 H NMR、粘度和密度测量研究了乙酸胆碱[Ch][OAc]。根据琼斯-多莱方程计算了粘度，并表明主要贡献来自短程离子-溶剂相互作用。从 NMR 化学位移滴定中分配了特定位置的缔合亲和力。在 DMSO-d 中，发现胆碱的羟基具有最小的离解常数，其次是乙酸的甲基。在低浓度下发现相应的吉布斯能量与溶剂分离的离子对（2SIP）构型一致，而在浓度高于 300mM 时，分配给溶剂共享的离子对（SIP）构型。对于 D O 中的[Ch][OAc]，缔合效应较弱，归因于溶剂的高介电常数。在 100ms 左右的时间尺度上，NMR 线宽扰动表明离子局部旋转动力学发生变化，归因于短程阳离子-溶剂相互作用，而不是溶剂粘度。在 184mM 时，在 DMSO-d 中 40%的阳离子和 D O 中的 10%的阳离子被发现表现出短程相互作用，如线宽扰动所表明的那样。发现大约在 300mM 时，离子在 DMSO-d 中在 400ms 左右的时间尺度上从自由到集体平移动力学转变。在 DMSO-d 中，两种离子都被发现几乎同等地溶剂化，而在 D O 中乙酸盐的溶剂化更强，如所获得的有效水动力半径所表明的那样。对于 DMSO-d 中的[Ch][OAc]，结果表明在 0.3-1M 之间的浓度下存在具有弱氢键相互作用的溶剂共享离子缔合。总体而言，预计溶剂如 DMSO 中的离子缔合程度不会显著限制电荷传输并阻碍胆碱基电解质的性能。
