An in situ XAS study of high surface-area IrO2 produced by the polymeric precursor synthesis

Anita Hamar Reksten; Andrea E. Russell; Peter W. Richardson; Stephen J. Thompson; Karina Mathisen; Frode Seland; Svein Sunde

doi:10.1039/D0CP00217H

An in situ XAS study of high surface-area IrO₂ produced by the polymeric precursor synthesis†

Anita Hamar Reksten,‡^a Andrea E. Russell,

^b Peter W. Richardson,^b Stephen J. Thompson,^b Karina Mathisen,^c Frode Seland^a and Svein Sunde

*^d

Author affiliations

* Corresponding authors

^a Department of Materials Science and Engineering, Norwegian University of Science and Technology (NTNU), NO-7491, Trondheim, Norway

^b Department of Chemistry, University of Southampton, Southampton SO17 1BJ, England, UK

^c Department of Chemistry, Norwegian University of Science and Technology (NTNU), NO-7491 Trondheim, Norway

^d Department of Materials Science and Engineering, Norwegian University of Science and Technology (NTNU), NO-7491, Trondheim, Norway
E-mail: svein.sunde@ntnu.no
Fax: +47 7359 1105
Tel: +47 7359 4051

Abstract

Iridium oxide powders with a surface area of more than 1 m² g⁻¹ (4 m² g⁻² from the H-UPD charge) and iridium-oxide crystallites less than 10 nm across were synthesized by heat treating gels formed from citric acid, ethylene glycol and dihydrogen hexachloroiridate(IV) in air. The characteristics of the resulting material was found to be strongly dependent on the heat-treatment step in the synthesis. A single heat-treatment of the gel resulted in a material with a substantial fraction of elemental iridium metal, i.e. iridium in oxidation state zero (Ir⁰). Post-synthesis modification of the powder by potential cycling resulted in oxidation peaks consistent with the conversion of the metal phase to iridium oxide. Linear combination of the near-edge part of the X-ray absorption data (X-ray absorption near-edge spectroscopy, XANES) collected in situ during potential cycling and an analysis of the extended X-ray fine-structure (EXAFS) part of the spectrum showed that the overall metal fraction was not significantly affected by the cycling. The oxidation of the metal phase is therefore limited to a thin layer of oxide at the metal surface, and a significant part of the iridium is left inactive. A modification of the heat treatment procedure of the sample resulted in iridium oxide containing only insignificant amounts of elemental iridium metal.

This article is part of the themed collection: Synchrotron Radiation Techniques in Catalytic Science

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Article information

DOI: https://doi.org/10.1039/D0CP00217H
Article type: Paper
Submitted: 14 Jan 2020
Accepted: 27 Mar 2020
First published: 30 Mar 2020

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Phys. Chem. Chem. Phys., 2020,22, 18868-18881

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An in situ XAS study of high surface-area IrO₂ produced by the polymeric precursor synthesis

A. H. Reksten, A. E. Russell, P. W. Richardson, S. J. Thompson, K. Mathisen, F. Seland and S. Sunde, Phys. Chem. Chem. Phys., 2020, 22, 18868 DOI: 10.1039/D0CP00217H

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