Counter Cations Affect Transport in Aqueous Hydroxide Solutions with Ion Specificity
Counter Cations Affect Transport in Aqueous Hydroxide Solutions with Ion Specificity
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DOI：
10.1021/jacs.8b13458
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发表时间：
2019-05-01
影响因子：
15
通讯作者：
Cremer, Paul S.
中科院分区：
文献类型：
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作者：
Drexler, Chad I.;Miller, Tierney C.;Cremer, Paul S.
氢氧化物和氢离子在水溶液中的异常高迁移率与质子转移和结构扩散有关。然而，在这些溶液中，反离子的作用通常被认为是微不足道的。在这里，我们探索碱金属反阳离子对氢氧化物溶剂化和迁移率的影响。阻抗测量表明，相对于钠和钾，锂会减弱氢氧化物的迁移率。这些结果被从头算分子动力学模拟和实验振动水合壳层光谱所解释，它们揭示了与其他阳离子相比，OH-和Li+之间更强的离子配对。水化壳层光谱和理论振动频率计算共同表明，锂离子和钠离子对氢氧化物上氢键贡献的水质子离域有不同的影响。具体地说，与钠相比，锂导致了质子离域的增强。然而，质子离域和整个扩散过程并不一定相关。
The anomalously high mobility of hydroxide and hydronium ions in aqueous solutions is related to proton transfer and structural diffusion. The role of counterions in these solutions, however, is often considered to be negligible. Herein, we explore the impact of alkali metal counter cations on hydroxide solvation and mobility. Impedance measurements demonstrate that hydroxide mobility is attenuated by lithium relative to sodium and potassium. These results are explained by ab initio molecular dynamics simulations and experimental vibrational hydration shell spectroscopy, which reveal substantially stronger ion pairing between OH- and Li+ than with other cations. Hydration shell spectra and theoretical vibrational frequency calculations together imply that lithium and sodium cations have different effects on the delocalization of water protons donating a hydrogen bond to hydroxide. Specifically, lithium leads to enhanced proton delocalization compared with sodium. However, proton delocalization and the overall diffusion process are not necessarily correlated.