A catalyst-coated mesoporous carbon–membrane electrode assembly for in situ soft X-ray XPS and NEXAFS studies of electrocatalytic interfaces

Counter, J. J. C. ORCID: https://orcid.org/0000-0001-8085-2972, Kumar, S. ORCID: https://orcid.org/0000-0002-1352-9945, Zalitis, C. M. ORCID: https://orcid.org/0000-0001-9139-2254, Clapp, M., Large, A. I. ORCID: https://orcid.org/0000-0001-8676-4172, Grinter, D. C. ORCID: https://orcid.org/0000-0001-6089-119X, van Spronsen, M. A. ORCID: https://orcid.org/0000-0002-5136-2816, Ferrer, P. ORCID: https://orcid.org/0000-0001-9807-7679, Karagoz, B., Erden, T. E., Bennett, R. A. ORCID: https://orcid.org/0000-0001-6266-3510 and Held, G. ORCID: https://orcid.org/0000-0003-0726-4183 (2026) A catalyst-coated mesoporous carbon–membrane electrode assembly for in situ soft X-ray XPS and NEXAFS studies of electrocatalytic interfaces. ACS Electrochemistry. ISSN 2997-0571 doi: 10.1021/acselectrochem.5c00554

Abstract/Summary

In situ soft X-ray spectroscopy provides direct insight into the electronic structure of electrocatalysts under realistic reaction conditions but remains technically challenging due to the need to combine aqueous electrochemistry with ultra-high-vacuum detection. Here, we present a mesoporous carbon–membrane working electrode assembly (WEA) that enables window-free in situ XPS and NEXAFS measurements during electrochemical reactions. The design integrates a Nafion proton-exchange membrane with a mesoporous carbon–ionomer contact layer and a thin IrOx catalyst layer, providing continuous electronic and protonic pathways and stable hydration through the membrane. By tuning the chamber water vapor pressure to 8 mbar, the WEA maintains a nanometer-thin water layer sufficient for the oxygen evolution reaction (OER) while preserving photoelectron detection efficiency. A robust peristaltic pump integrated with an alumina-bed water vapor dosing system maintains steady-state hydration at 6–10 mbar with <±0.1 mbar variation, enabling reproducible in situ spectra over extended periods. In situ Ir 4f and O 1s XPS reveal oxidation of Ir3+/Ir4+ to Ir4+/Ir5+ and dynamic changes in hydroxyl and lattice oxygen species, while O K-edge NEXAFS identify the formation of potential-stabilized μ2–O and μ1–O oxygen ligand species at OER. The WEA thus provides a quantitative, window-free platform for probing electrochemical interfaces under near-ambient conditions and establishes a general methodology for in situ soft X-ray studies of functional electrocatalysts, closely resembling the architecture and operation of industrial membrane-based water electrolyzers. This approach establishes a reliable methodology for coupling electrochemistry with the element specific soft X-ray spectroscopy under realistic reaction conditions.

Item Type	Article
URI	https://centaur.reading.ac.uk/id/eprint/129144
Identification Number/DOI	10.1021/acselectrochem.5c00554
Refereed	Yes
Divisions	Life Sciences > School of Chemistry, Food and Pharmacy > Department of Chemistry
Publisher	American Chemical Society
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