Catalysis for Energy Conversion
Abstract
The development of catalysts for the electrochemical synthesis of energy carriers is the subject of intensive research. The most common reaction in this context is splitting of water into H2 and O2. Technically, this reaction is already feasible at a large scale but it still suffers from a significant lack in efficiency due to the high overpotential for the anodic oxygen evolution reaction. Furthermore, scarce and expensive metals (Pt, Ru, Ir) are needed in state of the art proton-exchange membrane electrolyzers. Common candidates for replacement discussed in the literature are transition metal and f-group oxides but also homogeneous catalysts comprising a transition metal coordinated by porphyrines, terpyridines or other ligands have been considered. These screenings are complicated by the fact that even fundamental properties such as the reaction mechanism of the oxygen evolution reaction are still under discussion.
Besides the generation of H2 also the direct synthesis of alcohols and hydrocarbons through electrochemical CO2 reduction has been considered. This process is an appealing alternative to water splitting since it offers direct access to energy carriers which can be stored more easily and also provides an interesting route to valuable chemicals and precursors for organic synthesis. Taking for example CO2 reduction, the most commonly considered materials are for example transition metals like Cu or Ag or homogeneous catalysts such as transition metal porphyrin and phthalocyanine. However, despite intensive research, CO2 reduction is still far from being realized at a technical scale. Common problems comprise for example a low efficiency due to high overpotentials and a lack of product selectivity partly owing to the competition with the much more efficient H2 evolution reaction.
This project will contribute to the development of catalysts for the electrochemical and photochemical generation of renewable energy carriers through density functional theory (DFT) and time-dependent density functional theory (TD-DFT) modeling. This will be complemented by ab-initio molecular dynamics simulations (AIMD) to include a proper description of the solvation shell if deemed necessary. The most likely reaction paths may be extracted either from micro-kinetic modeling or kinetic Monte-Carlo simulations. Contrary to most other research groups, we will focus equally on homogeneous, solid-state and photocatalysts. This will enable us to identify similarities and differences between the different approaches for water splitting and CO2 reduction. Typical systems considered by us will for example comprise transition and f group metal oxides (MnOx, CoOx, IrOx, RuOx, CeOx, etc.) or homogeneous (photo-)catalysts (Ru, Co, Fe, Ir, etc. + porphyrin, phthalocyanine, terpyridine) Initial stages of the project will focus on generating a detailed mechanistic understanding of the reaction paths for the considered reactions. This understanding is then used to identify design criteria for improved catalysts and perform screening studies. The screening results will be analyzed using for example linear scaling relationships and volcano plots.
