水在电化学界面上的模拟研究
Water at an electrochemical interface - a simulation study
摘要：
描述了离子水溶液中靠近模型金属电极界面的水的性质的分子动力学模拟的结果。在模拟中，电极表现为理想的可极化的亲水性金属，支持图像电荷与带电物质的相互作用，并且其相对于溶液保持恒定的电势，使得该模型是电化学界面的教科书表示，其中没有电流通过。我们展示了水是如何被强烈吸引并在电极表面有序。这种顺序与从电极界面的连续模型中可能想象的结构不同。此外，这种排序显著影响离子到达表面的概率。我们描述了伴随的运动和配置的水和离子的电极电位的函数，我们分析了离子大气波动的长度尺度。这些波动的统计取决于表面结构和离子强度。波动很大，足以使平均离子气氛是一个贫穷的描述符的水环境附近的金属表面。这一发现的电化学反应的描述的重要性进行检查，通过计算，直接从模拟，马库斯自由能分布的电极和溶液中的氧化还原物种之间的电荷转移，并比较结果与连续理论的预测。从电化学教科书描述的现象显着偏离被发现，其物理起源的特征在于从原子的角度的模拟。
英文摘要：
The results of molecular dynamics simulations of the properties of water in an aqueous ionic solution close to an interface with a model metallic electrode are described. In the simulations the electrode behaves as an ideally polarizable hydrophilic metal, supporting image charge interactions with charged species, and it is maintained at a constant electrical potential with respect to the solution so that the model is a textbook representation of an electrochemical interface through which no current is passing. We show how water is strongly attracted to and ordered at the electrode surface. This ordering is different to the structure that might be imagined from continuum models of electrode interfaces. Further, this ordering significantly affects the probability of ions reaching the surface. We describe the concomitant motion and configurations of the water and ions as functions of the electrode potential, and we analyze the length scales over which ionic atmospheres fluctuate. The statistics of these fluctuations depend upon surface structure and ionic strength. The fluctuations are large, sufficiently so that the mean ionic atmosphere is a poor descriptor of the aqueous environment near a metal surface. The importance of this finding for a description of electrochemical reactions is examined by calculating, directly from the simulation, Marcus free energy profiles for transfer of charge between the electrode and a redox species in the solution and comparing the results with the predictions of continuum theories. Significant departures from the electrochemical textbook descriptions of the phenomenon are found and their physical origins are characterized from the atomistic perspective of the simulations.
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