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Assessing Optical and Electrical Properties of Highly Active IrOx Catalysts for the Electrochemical Oxygen Evolution Reaction via Spectroscopic Ellipsometry

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Velasco Vélez,  Juan
Inorganic Chemistry, Fritz Haber Institute, Max Planck Society;
Department of Heterogenous Reactions, Max Planck Institute for Chemical Energy Conversion;

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Citation

Sachse, R., Pflüger, M., Velasco Vélez, J., Sahre, M., Radnik, J., Bernicke, M., et al. (2020). Assessing Optical and Electrical Properties of Highly Active IrOx Catalysts for the Electrochemical Oxygen Evolution Reaction via Spectroscopic Ellipsometry. ACS Catalysis, 10(23), 14210-14223. doi:10.1021/acscatal.0c03800.


Cite as: http://hdl.handle.net/21.11116/0000-0007-A333-7
Abstract
Efficient water electrolysis requires highly active electrodes. The activity of corresponding catalytic coatings strongly depends on material properties such as film thickness, crystallinity, electrical conductivity, and chemical surface speciation. Measuring these properties with high accuracy in vacuum-free and non-destructive methods facilitates the elucidation of structure–activity relationships in realistic environments. Here, we report a novel approach to analyze the optical and electrical properties of highly active oxygen evolution reaction (OER) catalysts via spectroscopic ellipsometry (SE). Using a series of differently calcined, mesoporous, templated iridium oxide films as an example, we assess the film thickness, porosity, electrical resistivity, electron concentration, electron mobility, and interband and intraband transition energies by modeling of the optical spectra. Independently performed analyses using scanning electron microscopy, energy-dispersive X-ray spectroscopy, ellipsometric porosimetry, X-ray reflectometry, and absorption spectroscopy indicate a high accuracy of the deduced material properties. A comparison of the derived analytical data from SE, resonant photoemission spectroscopy, X-ray absorption spectroscopy, and X-ray photoelectron spectroscopy with activity measurements of the OER suggests that the intrinsic activity of iridium oxides scales with a shift of the Ir 5d t2g sub-level and an increase of p–d interband transition energies caused by a transition of μ1-OH to μ3-O species.