An in situ XAS study of high surface-area IrO2 produced by the polymeric precursor synthesis. Issue 34 (14th April 2020)

• Record Type: Journal Article
• Authors: Reksten, Anita Hamar; Russell, Andrea E.; Richardson, Peter W.; Thompson, Stephen J.; Mathisen, Karina; Seland, Frode; Sunde, Svein
• Is Part Of: Physical chemistry chemical physics. Volume 22:Issue 34(2020)
• Page Start: 18868
• Page End: 18881
• Publication Date: 2020-04-14
• Subjects: Chemistry, Physical and theoretical -- Periodicals; 541.3
• DOI: 10.1039/d0cp00217h
• Languages: English
• ISSNs: 1463-9076

Abstract

Abstract : In situ XAS measurements show that iridium oxide electrocatalysts manufactured by the polymeric precursor synthesis method contain a significant fraction of elemental iridium metal and that potential cycling only oxidises a thin layer of the elemental component of the composite. Abstract : Iridium oxide powders with a surface area of more than 1 m 2 g −1 (4 m 2 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 (Ir 0 ). 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.