Modeling of the electric double layer at metal oxide electrode/electrolyte interfaces with density functional theory based molecular dynamics

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Transition metal oxides play a prominent role in the design of new, efficient (photo) electrocatalysts demanded by the increased energy need and the related environmental issues in Germany and worldwide. Most earth-abundant metal oxides are only stable in alkaline solution (pH 14). Modeling and simulation of the electric double layer (EDL) formed by deprotonation of adsorbed water and hydroxide ions at the metal oxide electrode/electrolyte interfaces is therefore an integral part of optimizing the cost efficiency of energy conversion. However, the lack of a detailed atomistic understanding of metal oxide electrochemical interfaces under operating conditions considerably hampers progresses. Here, as the core objective of the project, I propose to develop and investigate the modeling of protonic EDL's using density functional theory (DFT) based molecular dynamics (MD) with explicit treatment of solvent. The focus will be on the dielectric properties of the EDL. As an example of high technological interest for photoelectrochemical energy conversion, we will study the protonic EDL at a model TiO2/electrolyte interface under the flatband conditions. By combining concepts of (single) electrode potentials in electrochemistry and Berry phase polarization in periodic systems for the first time, we expect to achieve a more realistic modeling of the EDL and ionic screening in the electrolytic solution. In particular, the proposed approach would enable us to charge the double layer at fixed chemical composition and compute the polarization as a new observable as well as the Helmholtz capacitance and the detailed spatial variation of the dielectric response in the double layer. This novel method will represent a considerable leap forward with respect to traditional continuum theories and current simplified atomistic supercell models. It would further lay down a valuable basis for future research towards a mechanistic understanding of the coupling of EDL with electrocatalytic processes, which is highly relevant for the design of efficient and economical electrocatalysts and photocatalysts.