B02: Element-Specific Electronic, Magnetic and Local Geometric Structure Effects in Mixed Oxide Catalysts

Prof. Dr. Heiko Wende

Our main goal for the second funding period is the extension of our local, element-specific methodology to catalysts in the liquid phase. The aim is to improve the catalysts’ performance while also encompassing the shift to different material systems that have gained importance within the CRC during the first funding period.

To achieve this transition from dry powder samples to liquid phase systems, we will construct a cell to enable in operando Mössbauer measurements of the Fe-containing catalyst material. Building on the results of our preliminary experiments, we aim to optimize the construction of this cell to achieve maximum efficiency in terms of reducing the time required to record spectra, maximizing the signal to noise ratio, and ensuring minimum non-resonant absorption and stray signals thanks to the use of mesh counter electrodes. Our other main goal consists of the in-depth characterization of catalyst materials from research area C with our new 10 T magnet cryostat, permitting a much more precise and detailed determination of the distribution of ions across crystallographic sites (degree of inversion for spinel systems). This is of particular importance for Co-rich systems that are currently of high interest for catalysis, with dramatic changes in underlying magnetic properties being used as a probe for the improvement of catalytic activity. Our ability to produce well-ordered Co-oxide reference systems with our pulsed laser deposition (PLD) system will provide additional possibilities to achieve a more detailed understanding of the local geometric and structural properties, enabling further optimization when selecting appropriate synthesis methods and material compositions for an increased catalytic efficiency. These films, along with selected samples produced within the CRC, are also to be characterized in the soft X-ray regime, utilizing X-ray magnetic circular dichroism (XMCD) to perform element-specific measurements even on Fe-free systems, which is of notable interest for Co-oxide catalysts as well as V-doped Co-oxides.

(Figure: Schematic depiction of proposed operando cell for Mössbauer measurements, with a movable radiation source. The cell stack with electrolyte flow (blue), working electrodes (black) with nanoparticle catalyst coating (green) and mesh counter electrodes (red) in front of a proportional counter).