Chemical Insights into the Formation of Colloidal Iridium Nanoparticles from In Situ X-ray Total Scattering: Influence of Precursors and Cations on the Reaction Pathway

Jette K. Mathiesen, Jonathan Quinson*, Sonja Blaseio, Emil T.S. Kjær, Alexandra Dworzak, Susan R. Cooper, Jack K. Pedersen, Baiyu Wang, Francesco Bizzotto, Johanna Schröder, Tiffany L. Kinnibrugh, Søren B. Simonsen, Luise Theil Kuhn, Jacob J.K. Kirkensgaard, Jan Rossmeisl, Mehtap Oezaslan, Matthias Arenz, Kirsten M.Ø. Jensen*

*Corresponding author for this work

Research output: Contribution to journalJournal articleResearchpeer-review


Iridium nanoparticles are important catalysts for several chemical and energy conversion reactions. Studies of iridium nanoparticles have also been a key for the development of kinetic models of nanomaterial formation. However, compared to other metals such as gold or platinum, knowledge on the nature of prenucleation species and structural insights into the resultant nanoparticles are missing, especially for nanoparticles obtained from IrxCly precursors investigated here. We use in situ X-ray total scattering (TS) experiments with pair distribution function (PDF) analysis to study a simple, surfactant-free synthesis of colloidal iridium nanoparticles. The reaction is performed in methanol at 50 °C with only a base and an iridium salt as precursor. From different precursor salts─IrCl3, IrCl4, H2IrCl6, or Na2IrCl6─colloidal nanoparticles as small as Ir∼55 are obtained as the final product. The nanoparticles do not show the bulk iridium face-centered cubic (fcc) structure but show decahedral and icosahedral structures. The formation route is highly dependent on the precursor salt used. Using IrCl3 or IrCl4, metallic iridium nanoparticles form rapidly from IrxClyn- complexes, whereas using H2IrCl6 or Na2IrCl6, the iridium nanoparticle formation follows a sudden growth after an induction period and the brief appearance of a crystalline phase. With H2IrCl6, the formation of different Irn (n = 55, 55, 85, and 116) nanoparticles depends on the nature of the cation in the base (LiOH, NaOH, KOH, or CsOH, respectively) and larger particles are obtained with larger cations. As the particles grow, the nanoparticle structure changes from partly icosahedral to decahedral. The results show that the synthesis of iridium nanoparticles from IrxCly is a valuable iridium nanoparticle model system, which can provide new compositional and structural insights into iridium nanoparticle formation and growth.
Original languageEnglish
JournalJournal of the American Chemical Society
Issue number3
Pages (from-to)1769-1782
Number of pages14
Publication statusPublished - 2023

Bibliographical note

We are grateful for funding from the Villum Foundation through a Villum Young Investigator Grant (VKR00015416). Funding from the Danish Ministry of Higher Education and Science through the SMART Lighthouse is gratefully acknowledged. We acknowledge support from the Danish National Research Foundation Center for High Entropy Alloy Catalysis (DNRF 149). M.A. received funding from the Swiss National Science Foundation (SNSF) via the project no. 200021 184742. The Danish Research Council is acknowledged for covering travel expenses in relation to the synchrotron experiment (DanScatt).


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