The development of continuum solvation models entailed two sub-projects. First, I have worked on the implementation and the validation of a hierarchy of electrolyte models. I have tested their ability to reproduce a representative experimental observable that is very sensitive on the details of the diffuse layer. Results suggest that only the most elaborate among the tested models is able to qualitatively reproduce all the experimentally-observed features. Second, I have collaborated in the development and implementation of a continuum-solvation technique that allows to deal with porous and open structures, enabling the treatment of a wide class of extended systems in combination with implicit solvation. This strategy guarantees that pockets that are smaller than a solvent molecule remain dielectric free.
The application of the developed continuum-solvation models entailed four sub-projects. The first sub-project involved a collaboration with the experimental group of Dr Katrin Domke (Max Planck Institute for Polymer Research, Mainz). In the collaboration, we targeted a prototypical electrochemical reaction. From the comparison between computed vibrational frequencies and Raman shifts obtained through operando experiments, we have identified some intermediates on the metal electrode surface that are likely to take part in the reduction process. In a second sub-project, we have worked in close collaboration with the group of Prof. Yang Shao-Horn (MIT) on a highly-relevant electrocatalytic process, i.e. the CO2 reduction reaction. Three catalyst materials have been considered and theoretically-computed surface-enhanced infrared absorption cross-sections compared to corresponding operando experiments. CO adsorbates have been identified on the Pt and Au surfaces, while various adsorbates have been observed on Cu. The third subproject focused on another highly-relevant process, i.e. the oxygen evolution reaction. Iridium oxide (IrO2) is the reference catalyst for this process, and for this reason extensive experimental work has been conducted on this system. Simulations of operando X-ray absorption near-edge structure (XANES) spectra have been carried out and compared to available experimental data. The comparison supports the formation of electron-deficient surface oxygen species in the OER-relevant voltage regime. Furthermore, surface hydroxyl groups are suggested to be progressively oxidized at larger potentials, giving rise to a shift in the Ir absorption cross-section that qualitatively agrees with measurements. In a final sub-project, an additional application of the continuum solvation models that is not directly related to electrochemistry has been developed. In particular, the use of a continuum embedding has been found effective in stabilizing negatively-charged configurations of isolated systems. Note that such configurations are typically predicted to be unbound by standard functionals in DFT.
The main form of dissemination has been represented by publications in scientific journals. In order to make the results of the project broadly available to any interested researcher the articles’ preprints have been made available through a public repository (arXiv). I have participated to the spring meeting of the German Physical Society (DPG), presenting the results of this project in the focus session “Frontiers of Electronic Structure: Focus on the Interface Challenge”. I have also been invited to give a MARVEL Junior Seminar at EPFL, where I had the chance to disseminate results to young researchers from diverse scientific backgrounds. The slides of the presentations have been made publicly available through the ResearchGate platform. All the scientific software implementations have been made publicly available through the GitHub and GitLab ENVIRON repositories, and corresponding updates published on the ENVIRON website (www.quantum-environment.org).
