Surface dynamics at electrochemical interfaces
1Institute of Experimental and Applied Physics, Kiel University, 24098 Kiel, Germany
Electrochemical interfaces are the key to many current and emerging technologies, for example in energy storage or micro-/nanofabrication. All of these applications involve atomic-scale processes on the electrode surface, such as the surface diffusion and mutual interactions of the atomic and molecular species, participating in the reactions. However, in contrast to adsorbate dynamics at solid surfaces under vacuum conditions, understanding of the surface dynamics at these complex interfaces is still rudimentary. Many aspects of the elementary dynamic events at electrochemical interface are unclear, for example: How is the motion of atoms across the surface affected by the presence of the electrolyte, in particular by coadsorbed species? Which role does the strong electric field at electrochemical interfaces play? What kinds of interactions between adsorbed species on the electrode surface exist, how strong are they, and what is their distance dependence? How do these effects influence electrochemical reactivity and the results of electrochemical reactions, e.g. the morphology of electrochemically deposited films?
A direct and powerful way to clarify such phenomena are direct observations of the atomic motion at the interface, provided the employed technique has a sufficient high spatial and temporal resolution for such studies. In the talk, I will discuss in situ studies of surface transport at electrochemical interfaces by high-speed scanning tunneling microscopy (Video-STM), which allows direct observations of the atomic-scale dynamics. By detailed statistical analysis, quantitative data on the diffusion barriers and interaction energies is obtained from these video data, providing insight into the role of the electrode potential and coadsorbed species. As examples, I will discuss the diffusion of isolated anionic, cationic, and organic adsorbates on noble metal electrodes as well as the interactions between identical and different adsorbate species [1-6]. These studies reveal a very strong dependence of the tracer diffusion of these adsorbates on the electrode potential, leading to changes in mobility over several orders of magnitude. Furthermore, coadsorbed anions can have a huge influence, leading to fundamentally different behavior even in systems, in which the adsorbate layers have identical structure.
To demonstrate the relevance of these observations for interfaces processes under technologically relevant conditions, case studies of electrochemical Au and Cu deposition by in situ x-ray surface scattering will be discussed [7-9]. They reveal surprising differences between Au and Cu electrodeposition, specifically an inverse potential dependence, demonstrating the pronounced influence of surface active coadsorbates on real-life electrode reactions.
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