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Probing catalytic surfaces by correlative scanning photoemission electron microscopy and atom probe tomography

MPS-Authors
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Schweinar,  Kevin
Atom Probe Tomography, Microstructure Physics and Alloy Design, Max-Planck-Institut für Eisenforschung GmbH, Max Planck Society;

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Nicholls,  Rachel L.
Inorganic Chemistry, Max Planck Institute for Chemical Physics of Solids, Max Planck Society;
Research Department Schlögl, Max Planck Institute for Chemical Energy Conversion, Max Planck Society;

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Rajamathi,  Catherine R.
Research Department Schlögl, Max Planck Institute for Chemical Energy Conversion, Max Planck Society;

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Raabe,  Dierk
Microstructure Physics and Alloy Design, Max-Planck-Institut für Eisenforschung GmbH, Max Planck Society;

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Greiner,  Mark
Research Department Schlögl, Max Planck Institute for Chemical Energy Conversion, Max Planck Society;

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Citation

Schweinar, K., Nicholls, R. L., Rajamathi, C. R., Zeller, P., Amati, M., Gregoratti, L., et al. (2020). Probing catalytic surfaces by correlative scanning photoemission electron microscopy and atom probe tomography. Journal of Materials Chemistry A, 8(1), 388-400. doi:10.1039/c9ta10818a.


Cite as: https://hdl.handle.net/21.11116/0000-0007-D38C-D
Abstract
The chemical composition and the electronic state of the surface of alloys or mixed oxides with enhanced electrocatalytic properties are usually heterogeneous at the nanoscale. The non-uniform distribution of the potential across their surface affects both activity and stability. Studying such heterogeneities at the relevant length scale is crucial for understanding the relationships between structure and catalytic behaviour. Here, we demonstrate an experimental approach combining scanning photoemission electron microscopy and atom probe tomography performed at identical locations to characterise the surface's structure and oxidation states, and the chemical composition of the surface and sub-surface regions. Showcased on an Ir-Ru thermally grown oxide, an efficient catalyst for the anodic oxygen evolution reaction, the complementary techniques yield consistent results in terms of the determined surface oxidation states and local oxide stoichiometry. Significant chemical heterogeneities in the sputter-deposited Ir-Ru alloy thin films govern the oxide's chemistry, observed after thermal oxidation both laterally and vertically. While the oxide grains have a composition of Ir0.94Ru0.06O2, the composition in the grain boundary region varies from Ir0.70Ru0.30O2 to Ir0.40Ru0.60O2 and eventually to Ir0.75Ru0.25O2 from the top surface into the depth. The influence of such compositional non-uniformities on the catalytic performance of the material is discussed, along with possible engineering levers for the synthesis of more stable and reactive mixed oxides. The proposed method provides a framework for investigating materials of interest in the field of electrocatalysis and beyond.