Mechanisms of adsorbate diffusion at electrochemical interfaces

电化学界面吸附物扩散机制

• 批准号: 504552981
• 负责人: Professor Dr. Olaf Magnussen
• 金额: --
• 依托单位: Institut für Experimentelle und Angewandte Physik
• 依托单位国家: 德国
• 项目类别: Research Grants
• 资助国家: 德国
• 项目状态: 未结题
• 来源: https://gepris.dfg.de/gepris/projekt/504552981?language=en
• 关键词: Mechanisms; adsorbate; diffusion; electrochemical; interfaces

The diffusion of adsorbates on electrode surfaces in contact with aqueous electrolytes is a central elementary process in many electrochemical reactions but is still poorly understood. It is known that the high electric fields and the presence of coadsorbed species strongly influence surface transport at electrochemical interfaces. This results in a pronounced potential dependence of the diffusion rates and in a complex influence of the electrolyte composition. In particular chemisorbed anions, which are widespread in natural and technological systems, affect surface diffusion distinctly. As shown in our previous work, these effects are currently unpredictable and often surprising. In some cases, the anion species can even determine the sign of the potential dependence. In this project, we propose to address the role of anions in surface diffusion by combining in situ atomic-resolution microscopic studies with ab initio calculations. Experimentally, we will determine the diffusion rates quantitatively as a function of potential by direct observations of the adsorbates’ motion with high-speed scanning tunneling microscopy. Density functional theory will be used to calculate the energy barriers of different diffusion pathways and the associated surface dipole moment changes, which provide a measure for the influence of the electric field, i.e., for potential effects. We will apply these methods to well-defined electrochemical systems: sulfide and methyl thiolate diffusion on halide-covered (100) surfaces of gold, silver, and copper. With this approach, we aim to clarify the following specific questions: What is the influence of the halide coadsorbate coverage on the adsorbate’s surface mobility? Why does the diffusion rate increase with potential in the presence of a disordered mobile halide layer, whereas it decreases in the potential regime of ordered adlayers at saturation coverage. How does the type of structural order in the halide adlayer affects the potential-dependence and the mechanisms of surface diffusion? Can anisotropic diffusion be induced this way and tuned by the potential? What is the origin of the halide-dependent inversion of the potential dependence of sulfide diffusion on Cu(100)? Can this effect be also observed in other adsorbate systems and is it related to a halide-induced change in the diffusion mechanism? What is the role of water in the diffusion process?We will address these questions by studies of carefully selected systems, including studies of halide-free reference systems. The obtained results should resolve current mysteries in surface transport at electrochemical interfaces by providing insights into the microscopic diffusion mechanisms. This will contribute to a better fundamental understanding of these important elementary processes and thus provides a basis for tuning surface transport in electrochemical reactions by the potential and additives.

在许多电化学反应中，吸附物在与电解液接触的电极表面的扩散是一个中心的基本过程，但人们对此仍知之甚少。众所周知，高电场和共吸附物种的存在对电化学界面的表面传输有很大的影响。这导致了扩散速率的显著的潜在依赖性以及电解液成分的复杂影响。尤其是化学吸附的阴离子，广泛存在于自然和技术体系中，对表面扩散有明显的影响。正如我们之前的工作所显示的，这些影响目前是不可预测的，而且往往令人惊讶。在某些情况下，阴离子物种甚至可以决定潜在依赖的标志。在这个项目中，我们建议通过结合原位原子分辨微观研究和从头计算来研究阴离子在表面扩散中的作用。在实验上，我们将通过用高速扫描隧道显微镜直接观察吸附物的运动来定量地确定作为势的函数的扩散速率。密度泛函理论将被用来计算不同扩散路径的能垒和与之相关的表面偶极矩变化，这为电场的影响，即势效应提供了一个量度。我们将把这些方法应用于明确定义的电化学系统：硫化物和甲硫醚在金、银和铜的卤化物覆盖的(100)表面上的扩散。通过这种方法，我们的目标是澄清以下具体问题：卤化物共吸附的覆盖度对吸附物的表面流动性有什么影响？为什么在无序流动卤化物层存在的情况下，扩散速率随势的增加而增加，而在饱和覆盖的有序附层的势区，扩散速率则减小。卤化物层中结构有序的类型如何影响表面扩散的势依赖性和机制？各向异性扩散能以这种方式被诱导并被势能调谐吗？硫化物扩散对铜(100)势能依赖性的卤化物依赖反转的来源是什么？这种影响是否也能在其他吸附体系中观察到？它是否与卤化物引起的扩散机制改变有关？水在扩散过程中的作用是什么？我们将通过对精心挑选的体系的研究，包括对无卤化物参比体系的研究，来解决这些问题。通过对微观扩散机制的洞察，所获得的结果应该能够解开电化学界面表面传输中的当前谜团。这将有助于更好地从根本上理解这些重要的基本过程，从而为通过电势和添加剂调节电化学反应中的表面传输提供基础。