How the anisotropy of surface oxide formation influences the transient activity of a surface reaction

P Winkler,J Zeininger,G Rupprechter,Y Suchorski,L Gregoratti,M Stöger-Pollach,M Amati,P Zeller

doi:10.1038/s41467-020-20377-9

P Winkler, J Zeininger + Show 6 more

Open Access

https://doi.org/10.1038/s41467-020-20377-9

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Abstract

Scanning photoelectron microscopy (SPEM) and photoemission electron microscopy (PEEM) allow local surface analysis and visualising ongoing reactions on a µm-scale. These two spatio-temporal imaging methods are applied to polycrystalline Rh, representing a library of well-defined high-Miller-index surface structures. The combination of these techniques enables revealing the anisotropy of surface oxidation, as well as its effect on catalytic hydrogen oxidation. In the present work we observe, using locally-resolved SPEM, structure-sensitive surface oxide formation, which is summarised in an oxidation map and quantitatively explained by the novel step density (SDP) and step edge (SEP) parameters. In situ PEEM imaging of ongoing H2 oxidation allows a direct comparison of the local reactivity of metallic and oxidised Rh surfaces for the very same different stepped surface structures, demonstrating the effect of Rh surface oxides. Employing the velocity of propagating reaction fronts as indicator of surface reactivity, we observe a high transient activity of Rh surface oxide in H2 oxidation. The corresponding velocity map reveals the structure-dependence of such activity, representing a direct imaging of a structure-activity relation for plenty of well-defined surface structures within one sample.

Highlights

Scanning photoelectron microscopy (SPEM) and photoemission electron microscopy (PEEM) allow local surface analysis and visualising ongoing reactions on a μm-scale
The surface oxidation of Rh and the structure of the resulting surface oxides has been previously studied via various experimental methods, focusing on well-defined Rh single crystal surfaces of mainly low
After oxidation at T = 623 K, pO2 = 2.5 × 10−4 mbar, t = 90 min, i.e., under conditions similar to those reported for trilayer oxide growth on single crystals[7,11,12], local X-ray photoelectron spectroscopy (XPS) spectra were measured for a 0.13 μm diameter spot on each 8 × 8 μm[2] sample area by scanning photoelectron microscopy (SPEM)

Summary

Introduction

Scanning photoelectron microscopy (SPEM) and photoemission electron microscopy (PEEM) allow local surface analysis and visualising ongoing reactions on a μm-scale. The very same Rh sample was used in the EBSD, SPEM and PEEM experiments, and even the same field of view was monitored, allowing a direct correlation between the local crystallographic structure and SPEM and PEEM data of local oxidation and reaction kinetics, respectively.

Results

Conclusion