Inorganic Functional Materials Research Institute, National Institute of Advanced Industrial Science and Technology (AIST), Ikeda, Osaka 563-8577, Japan.
Department of Chemistry, School of Science and Technology, Kwansei Gakuin University, Sanda, Hyogo 669-1337, Japan.
J Chem Phys. 2019 Sep 14;151(10):104704. doi: 10.1063/1.5113738.
Hydration of monovalent (Li, Na, K, and Cs) and divalent (Mg, Ca, Sr, and Ba) cations on a cathode surface was studied by a classical molecular dynamics simulation. The potential of mean force (PMF) for each cation species was calculated as a function of the distance from the cathode surface, and the potential barriers for dehydrating the first and second hydration shells near the cathode surface were estimated. The positions of the minimum of the PMF closest to the cathode surface were found to be in the order Li < Na < Mg < Ca < Sr < Ba < K < Cs. It was found that Li, Mg, Ca, Sr, and Ba ions are most likely doubly hydrated when they are adsorbed on the cathode surface without an applied voltage, whereas Na, K, and Cs ions are most likely singly hydrated at room temperature. On the other hand, when a voltage of 1 V was applied to the electrodes, all the cation species that we studied appeared most likely to be singly hydrated on the cathode surface. The depths of the potential well closest to the cathode surface under an applied voltage of 1 V were found to be in the order Ba < Sr < Ca < Mg for the divalent cations and Li < Na < K < Cs for the monovalent cations in the set of models that we used. These orders coincide with the Hofmeister series from the kosmotropic to the chaotropic.
通过经典分子动力学模拟研究了一价（Li、Na、K 和 Cs）和二价（Mg、Ca、Sr 和 Ba）阳离子在阴极表面的水合作用。计算了每种阳离子物种的平均力势（PMF）随距离阴极表面的函数关系，并估计了靠近阴极表面的第一层和第二层水合壳脱水的势垒。发现最接近阴极表面的 PMF 最小值的位置按 Li < Na < Mg < Ca < Sr < Ba < K < Cs 的顺序排列。结果表明，在没有外加电压的情况下，当这些离子被吸附在阴极表面时，Li、Mg、Ca、Sr 和 Ba 离子最有可能双水合，而在室温下，Na、K 和 Cs 离子最有可能单水合。另一方面，当电极施加 1 V 的电压时，我们研究的所有阳离子物种在阴极表面最有可能单水合。发现施加 1 V 电压时最接近阴极表面的势阱深度按 Ba < Sr < Ca < Mg 的顺序排列，对于二价阳离子，而对于一价阳离子，则按 Li < Na < K < Cs 的顺序排列。这些顺序与从亲核性到亲脂性的豪夫迈斯特序列一致。
