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Abstract

For heterogeneous (electro)catalysis, the catalytic properties of a material are foremost determined by its structure and composition at the interface between the catalyst and the reaction environment. However, both the structure and composition are not static factors, but parameters that respond dynamically to their environment. A deeper understanding of these dynamic processes is therefore required to be able to, in turn, make targeted improvements to electrocatalytic materials. Here, three projects are presented that each address the surface alterations that result from specific catalyst functionalization and activation treatments. First, we show the oxidation of Cu(100) and Cu(111) surfaces via a low-pressure O₂-plasma treatment, investigated by scanning tunneling microscopy, x-ray spectroscopy and low energy electron diffraction. We traced the evolution of Cu, Cu₂O and CuO and the surface structure over time and found that the surface orientation plays a critical role in the time-dependent oxidation process. The results show that initial surface reconstruction is accompanied by island growth, coalescencing into a thin layer for longer exposure times. The composition trace reveals an initial Cu₂O overlayer until eventually a thicker CuO is grown on top of it. The second study investigates the effects of a pulsed potential on the surface morphology of a Cu(100) single crystal. The stepped surface of a UHV-prepared crystal experiences large alterations in the form of cubic protrusions evolving during the pulsed potential in a certain potential window, resulting in a reconstructed surface and highly reactive structural motifs. We also identified key potentials and pulse durations and their corresponding structural changes to allow for separation of morphological from oxidation state effects in future studies. In the final project, nuclear resonant inelastic X-ray scattering (NRIXS) and X-ray absorption fine-structure spectroscopy (XAFS) measurements were employed to gain insight into the dynamic structure and surface composition of FeCu and FeAg nanoparticles under CO₂RR conditions. We also extracted their correlations with the catalytic activity and selectivity. The formation of a core-shell structure during CO₂RR for FeAg NP was inferred from the phonon density of states (PDOS), extracted from NRIXS data, and XAFS measurements.