Visualization of Solvent Structures at Electrified Solid-Liquid Interfaces via Electrochemical Atomic Force Microscopy

Andrea Auer^a, Thorben Eggert^b, Nicolas G. Hörmann^b, Karsten Reuter^b, Franz J. Giessibl^c

^aInsitute of Physical Chemistry, University of Innsbruck, Austria

^bFritz-Haber-Institut der Max-Planck-Gesellschaft, Berlin, Germany

^cInstitute of Experimental and Applied Physics, University of Regensburg, Germany

Materials for Sustainable Development Conference (MATSUS)
Proceedings of MATSUS Fall 2024 Conference (MATSUSFall24)

#EEInt - Electrode-Electrolyte Interfaces in Electrocatalysis

Lausanne, Switzerland, 2024 November 12th - 15th

Organizers: Yu Katayama and Mariana Monteiro

Invited Speaker, Andrea Auer, presentation 111
DOI: https://doi.org/10.29363/nanoge.matsusfall.2024.111
Publication date: 28th August 2024

For the development of efficient electrochemical interfaces, which are vital for sustainable energy technologies, it is essential to accurately identify the molecular structure of the electric double layer, a critical region where all electrocatalytic reactions occur. While current electrochemical scanning probe microscopy techniques are effectively used to examine structural changes on an electrode surface, even under reaction conditions, they generally lack sensitivity to the solvent structure on the liquid side. Conversely, high-resolution atomic force microscopy (AFM) has demonstrated the ability to visualize the vertical arrangement of solvent molecules perpendicular to the surface, as shown, for example, in Ref. [1]. Nonetheless, there are only a limited number of studies that explore this capability with potential control in an operating electrochemical cell. In this study, we utilize electrochemical AFM equipped with stiff qPlus sensors[2,3] to investigate the potential-dependent solvent layering at clearly defined electrified solid-liquid interfaces with high spatial precision. Our experiments on Au(111) electrodes in various aqueous electrolytes demonstrate pronounced oscillatory shifts in frequency along the z-axis (normal to the surface plane). These shifts, influenced by the electrode's charge, the applied potential, and the specific ions present, are attributed to the layering of water and/or ions near the electrode surface. The observations are supported by corresponding atomistic molecular dynamics simulations.

References:

[1] Fukuma T.; Garcia R. Atomic- and Molecular-Resolution Mapping of Solid–Liquid Interfaces by 3D Atomic Force Microscopy. ACS Nano 2018 ,12, 11785–11797.

[2] Giessibl, F. J. The qPlus sensor, a powerful core for the atomic force microscope. Rev. Sci. Instrum. 2019, 90, 011101.

[3] Auer, A.; Eder, B.; Giessibl, F.J. Electrochemical AFM/STM with a qPlus sensor: A versatile tool to study solid-liquid interfaces. J. Chem. Phys. 2023, 159, 174201.

Acknowledgements:

A.A. gratefully acknowledges funding from the Alexander von Humboldt Foundation via the Research Fellowship Program. This research was funded in part by the Austrian Science Fund (FWF) 10.55776/COE5.

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