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The interaction between ions and solvents in solution is a basic scientific issue that has received extensive attention in many important areas of national economy such as energy, catalysis, materials, medicine, and so on. For example, the recent emergence of water-based alkaline metal ion batteries uses a highly concentrated aqueous ion solution as an electrolyte, which is safer, more inexpensive, and more efficient than conventional ion batteries. A deep understanding of the interactions and correlations between ions in the solution and the surrounding water molecules is essential for a deep understanding of the molecular mechanisms of the electrochemical and charge transport efficiency at the electrode interface of the battery and the design of more efficient batteries. significance. Another example is the presence of various ionic ligands (eg, I-, etc.) in many homogeneous or solid-liquid heterogeneously catalyzed reaction systems. Reactions occurring in the same type of ion-pair functional motif can be changed from poisoning to promotion under different conditions. The various very different roles. The microscopic description of the structural causes of these effects is of great significance for understanding the functional mechanisms of the functional elements and their mutual cooperation mechanisms.
There is a very controversial basic question in the study of the ion effect of solution, namely how to understand the influence of cations on the dynamic behavior of water molecules. For this problem, different experimental methods often give different images. For example, for two very similar alkali metal ions, Na+ and K+, neutron scattering experiments have determined that they have similar structural damage to water, so they are thought to accelerate the rotational motion of water; while NMR and ultrafast lasers Spectrodynamic experiments have detected that Na+ will slow down and K+ will accelerate the rotation of water molecules. A deep understanding of this issue has become particularly important because of the significant role of these two alkali metal ions in energy, electrochemistry, and life sciences.
Under the auspices of the Chinese Academy of Science's Strategic Pilot Science and Technology Project and National Natural Science Foundation of China's Key and General Program, the Zhuang Kai Group of the State Key Laboratory of Structural Chemistry of the Institute of Physical Structure Research of the Chinese Academy of Sciences and the Ultrafast Laser Spectroscopy Experimental Team of Peking University Cooperation has theoretically explained the causes of the above-mentioned contradictory phenomena. On the basis of large-scale classical and quantum molecular dynamics simulations, combined with the Extended Ivanov Jump theoretical analytical model, they discovered that both ions accelerate the large-angle-jumping rotation of adjacent water molecules due to the destruction of hydrogen bonds in water. The sub-scattering results are consistent. On the other hand, they have different effects on the diffusion kinetics of water molecules: Na+ slows the diffusion of water, and K+ promotes this rotation, which is consistent with the kinetic experimental results. The above conclusions provide a reasonable picture for explaining the apparent contradiction between the two types of experimental observational assertions. The relevant research results are published in the Journal of Chemical Science (DOI:10.1039/C6SC03320B).
This work is the latest development of this research group in this direction since 2010. Previous research results include the combination of ultrafast spectroscopy experiments to find that ion clusters are still present even in the lower concentration of strong electrolyte solutions. The phenomenon of clustering (PNAS 108, 4737, 2011), and because of the subversive significance of this finding to the classic images in textbooks, was reported in the "Science" magazine monograph (DOI: 10.1126/science.331.6024.1495-a).
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