Strategies for the analysis of the elemental metal fraction of Ir and Ru oxides via XRD, XANES, and EXAFS

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

doi:10.1039/c9cp01758e

Strategies for the analysis of the elemental metal fraction of Ir and Ru oxides via XRD, XANES, and EXAFS

Phys Chem Chem Phys. 2019 Jun 21;21(23):12217-12230. doi: 10.1039/c9cp01758e. Epub 2019 Jun 3.

Authors

Anita Hamar Reksten¹, Andrea E Russell², Peter W Richardson², Stephen J Thompson², Karina Mathisen³, Frode Seland¹, Svein Sunde⁴

Affiliations

¹ Department of Materials Science and Engineering, Norwegian University of Science and Technology (NTNU), NO-7491, Trondheim, Norway.
² Department of Chemistry, University of Southampton, Southampton SO17 1BJ, England, UK.
³ Department of Chemistry, Norwegian University of Science and Technology (NTNU), NO-7491 Trondheim, Norway.
⁴ Department of Materials Science and Engineering, Norwegian University of Science and Technology (NTNU), NO-7491, Trondheim, Norway. svein.sunde@ntnu.no.

PMID: 31157341
DOI: 10.1039/c9cp01758e

Abstract

Iridium and ruthenium oxide are active electrocatalysts for oxygen evolution. The relation between preparation method, structure, and behavior of mixed oxides of iridium and ruthenium are of interest in order to obtain active and stable catalysts. In this work the structure of mixed Ru-Ir oxides synthesized by the polymeric precursor method, which involves the formation of a gel containing the metal precursors and subsequent heat-treatment in air, was studied for the Ir_xRu_1-xO₂ system. An in-depth analysis of X-ray diffraction (XRD) and X-ray absorption (XAS) data, including EXAFS and linear combination of XANES, shows that the polymeric precursor synthesis method is capable of providing an intimate mixing of Ir and Ru in the catalyst. In addition to the oxide phase, metal phases, i.e. with Ru or Ir or both in oxidation state zero (Ir(fcc) and Ru(hcp)), were also found in the product materials. Facing complex structures such as some of those synthesized here, we have shown that a representation of shells with more than one atom type are efficiently represented using mixed sites, i.e. including scattering contributions from several elements in a site corresponding to a partial occupancy of the site by these elements, this method forming a very efficient basis for analyzing EXAFS data.