Interplay of Chemical Reactions and Electricity

In electrochemistry, chemical processes interact with an external voltage. If energy is released, it can be harnessed, and we have a battery or fuel cell. If energy is consumed, it drives reactions and converts chemical substances (electrolysis, electrosynthesis).

The change from conventional to renewable energy supply and the rapid depletion of fossil resources caused much attention to electrochemistry in recent years. Energy storage and mobility require new, more efficient batteries. Electrolysis is crucial in enabling the change from fossil resources to renewables. Hence, further improvements in the field of electrochemistry are necessary.

Many electrochemical processes are not well understood. The reasons are, among other things, the short lifetimes of reactive intermediates and the complexity of the heterogeneous electron transfer from the electrode to the electrolyte. Both limit the experimental techniques that can be used to study electrochemical processes. For that purpose, simulations provide fundamental insights into the ongoing processes.

Example of a Pourbaix-type diagram. It provides the areas of stability of different reduced and protonated forms of a species. The data can be obtained experimentally or by simulations.

We aim to understand electrochemical processes occurring in electrolyte solutions using quantum chemistry as a molecular microscope. In doing so, we study chemical reactions at the atomic scale. Our research interest thereby spans both batteries and electrolysis.

The unifying element of our research activities is the development of novel concepts, which allow for a direct comparison of calculated properties from our models with experimental data (i.e., discharge curves, acid/base-, and redox properties), connecting simulation and experiment. Simultaneously, we aim to construct reliable models for electrochemical processes involved in batteries and electrolysis, providing fundamental insight at the atomic scale.

In battery research, we delve into novel cell systems, which command significant attention in a broad research community. At the atomic scale, we simulated the impact of ion mobility in sodium-sulfur cells and explored the dependency on ion mobility of electrolyte components such as the supporting electrolyte or innovative specialized electrolytes. Another focal area of interest involves examining the redox behavior of lithium-sulfur cells. In pursuit of that research objective, we model the entire discharge mechanism contingent upon various electrolytes and leverage the insights gained from these investigations to draw direct comparisons with experimental data, simulating discharge profiles.

Our primary research foci within electrolysis are electrocatalysis (i.e., electrocatalytic hydrogen evolution reaction) and organic electrosynthesis (e.g., the Kolbe reaction). As these reactions involve multiple proton- and electron-transfer steps, we develop a generalized method called Pourbaix-type diagrams, which allows for the combined study of a chemical system's acid/base- and redox characteristics. With that method, we can represent the thermodynamic and kinetic properties of the occurring chemical process. Additionally, a further generalization to a Lewis definition of acid/base chemistry and photoredox, as well as photoelectrochemistry, is possible.

We applied that method to metalloporphyrin catalysts for electrocatalytic hydrogen evolution reaction. Our investigations revealed the importance of considering the interdependence of proton and electron transfers and the non-innocent role of the supporting electrolytes.

Moreover, we studied the electrochemical trifluoromethylation of imidazoles as an exemplary reaction in the field of organic electrosynthesis. That reaction is not only of high synthetic value but also a readily chosen reaction for photoredox catalysis.

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