Gouverneur Martin, Kopp Jakob, van Wüllen Leo, Schönhoff Monika
Institute of Physical Chemistry, University of Muenster, Corrensstraße 28/30, 48419 Münster, Germany.
Institute of Physics, Augsburg University, Universitätsstraße 1, 86159 Augsburg, Germany.
Phys Chem Chem Phys. 2015 Nov 11;17(45):30680-6. doi: 10.1039/c5cp05753a.
Charge transport in ionic liquids is a phenomenon of utmost interest for electrochemical (e.g. battery) applications, but also of high complexity, involving transport of ion pairs, charged clusters and single ions. Molecular understanding is limited due to unknown contributions of cations, anions and clusters to the conductivity. Here, we perform electrophoretic NMR to determine electrophoretic mobilities of cations and anions in seven different ionic liquids. For the first time, mobilities in the range down to 10(-10) m(2) V(-1) s(-1) are determined. The ionic transference number, i.e. the fractional contribution of an ionic species to overall conductivity, strongly depends on cation and anion structure and its values show that structurally very similar ionic liquids can have cation- or anion-dominated conductivity. Transference numbers of cations, for example, vary from 40% to 58%. The results further prove the relevance of asymmetric clusters like CationXAnionY, X ≠ Y, for charge transport in ionic liquids.
离子液体中的电荷传输是电化学（如电池）应用中极其重要的现象，但同时也具有高度复杂性，涉及离子对、带电簇和单离子的传输。由于阳离子、阴离子和簇对电导率的贡献未知，分子层面的理解受到限制。在此，我们进行了电泳核磁共振实验，以确定七种不同离子液体中阳离子和阴离子的电泳迁移率。首次测定了低至10^(-10) m^(2) V^(-1) s^(-1)范围内的迁移率。离子迁移数，即离子物种对总电导率的分数贡献，强烈依赖于阳离子和阴离子结构，其值表明结构非常相似的离子液体可能具有以阳离子或阴离子为主导的电导率。例如，阳离子的迁移数在40%至58%之间变化。结果进一步证明了像[阳离子X阴离子Y](X - Y)（X≠Y）这样的不对称簇在离子液体电荷传输中的相关性。
