Using X-Ray Absorption Spectroscopy to Understand Thin Film Electrocatalysts
CatLab Lectures 2024/25
- Date: Nov 1, 2024
- Time: 10:30 AM - 12:00 PM (Local Time Germany)
- Speaker: Dr. Marcel Risch
- Helmholtz-Zentrum Berlin
- Location: Building M, Richard-Willstätter-Haus, Faradayweg 10, 14195 Berlin
- Room: seminar room, 1st floor
- Host: HZB and FHI
- Contact: trunschk@fhi-berlin.mpg.de
The combination of electrochemical methods (EC) and X-ray absorption spectroscopy (XAS) is a powerful approach to understand electrocatalysis on an atomistic level. While electrochemistry registers electrons that are passed through the external circuit, the element-specific XAS can pinpoint the source or sink of these electrons, i.e. identify the electrochemically active element or elements under and given condition.
Additionally, the analysis of the extended X-ray absorption fine structure (EXAFS) encodes the local structure in the vicinity of the active elements, which works without the need for global long-range order in the studied material. While the combined EC-XAS approach is applicable to a very wide spectrum of matter from liquids to soft matter to crystals, I focus in this presentation on catalytic insight into thin films with width <100 nm with and without long-range order. XAS has high probing depth exceeding these film thicknesses multiple times. In order to improve the contribution from the surface where catalysis occurs, we measured either porous thin films with high surface area or atomically flat thin films in grazing incidence configuration or differential XAS. These recent results highlight that the electrocatalysts during or after catalyzing the oxygen evolution reaction (OER) differ significantly from the as- synthesized materials. In particular, I will highlight the role of Co(IV) for OER electrocatalysis and the in situ formation of a few monolayers of Ni oxyhydroxide on LaNiO3 as well as give an outlook on future operando investigations.