Structure-Potential Relationships of Electrochemical Interfaces by in situ Reflection Anisotropy Spectroscopy

• Applicant: Dr. Matthias May
• Subject Area: Physical Chemistry of Solids and Surfaces, Material Characterisation ; Theoretical Chemistry: Molecules, Materials, Surfaces
• Term: since 2020
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 434023472

The electrochemical double layer (EDL) with its adsorbed ions and strong electric fields is the central aspect of (photo)electrochemical energy conversion in the form of water splitting or batteries. Fundamental processes at this solid-liquid interface are, however, still not fully understood. Especially the microscopic description of the (electronic) structure as a function of the electrode potential in the electrolyte is hitherto only possible to a limited extent, both from an experimental and a theoretical point of view. This is where the present proposal comes in and will provide new insights by closely coupling experimental with theoretical spectroscopy.Understanding the microscopic behaviour of potential-dependent ion-adsorption processes from the electrolyte as well as reordering, oxidation or corrosion of the solid surface requires access to the EDL with high spatial and temporal resolution. The interpretation of experimental spectra in context of electronic structure modelling and subsequent derivation of theoretical spectra can significantly extend this understanding. The experimental access to the EDL at the required resolution and information depth is challenging and requires the use of complementary methods. The modelling of the electronic structure by density functional theory (DFT), on the other hand, faces the challenge to define the electrode potential under three-dimensional periodic boundary conditions and to describe the excited state quantitatively accurately for the spectroscopy.This is where reflection anisotropy spectroscopy (RAS) comes in as an in situ method for the study of electrochemical interfaces. The intrinsically very high spatial and adequate temporal resolution enables the access to surface reconstructions, band bending, dipoles, and electric fields in the EDL. As a differential spectroscopy of linear optical nature, it furthermore provides a direct link to the DFT-based model of the electronic structure with quantitative significance. Theoretical RAS is, however, not yet established for electrochemical systems, where a combination with molecular dynamics simulations is required, which is why this development will be a central aspect here. Initial reference systems for method development will be experiments on the semiconductors InP and Si in aqueous and organic electrolytes. These studies will be extended later on to further materials such as Mg. The close coupling of experiment and modelling will for one thing allow to gain a microscopic view of the EDL as a function of the potential from the experimental spectra. On the other hand, this strategy will provide a way to validate the applied theoretical approaches.The insights gained in the course of this project will both allow to design (photo)electrodes in a more controlled manner and set incentives for further developments towards an atomistic theory of electrochemistry.

• DFG Programme: Independent Junior Research Groups
• International Connection: Italy, United Kingdom, USA
• Major Instrumentation: RA Spektrometer
• Instrumentation Group: 5360 Meßgeräte für gestreutes und reflektiertes Licht, optische Oberflächen-Prüfgeräte
• Cooperation Partners: Dr. Conor Hogan; Professor Michiel Sprik, Ph.D.; Dr. Matt Watkins