Nanoscopic Porous Iridium/Iridium Dioxide Superstructures (15 nm): Synthesis and Thermal Conversion by In Situ Transmission Electron Microscopy

Kevin Pappert, Kateryna Loza, Meital Shviro, Ulrich Hagemann, Marc Heggen, Rafal E. Dunin-Borkowski, Roland Schierholz, Takuya Maeda, Kenji Kaneko, Matthias Epple

    Research output: Contribution to journalArticlepeer-review

    4 Citations (Scopus)

    Abstract

    Porous particle superstructures of about 15 nm diameter, consisting of ultrasmall nanoparticles of iridium and iridium dioxide, are prepared through the reduction of sodium hexachloridoiridate(+IV) with sodium citrate/sodium borohydride in water. The water-dispersible porous particles contain about 20 wt % poly(N-vinylpyrrolidone) (PVP), which was added for colloidal stabilization. High-resolution transmission electron microscopy confirms the presence of both iridium and iridium dioxide primary particles (1–2 nm) in each porous superstructure. The internal porosity (≈58 vol%) is demonstrated by electron tomography. In situ transmission electron microscopy up to 1000 °C under oxygen, nitrogen, argon/hydrogen (all at 1 bar), and vacuum shows that the porous particles undergo sintering and subsequent compaction upon heating, a process that starts at around 250 °C and is completed at around 800 °C. Finally, well-crystalline iridium dioxide is obtained under all four environments. The catalytic activity of the as-prepared porous superstructures in electrochemical water splitting (oxygen evolution reaction; OER) is reduced considerably upon heating owing to sintering of the pores and loss of internal surface area.

    Original languageEnglish
    Pages (from-to)11048-11057
    Number of pages10
    JournalChemistry - A European Journal
    Volume25
    Issue number47
    DOIs
    Publication statusPublished - Aug 22 2019

    All Science Journal Classification (ASJC) codes

    • Catalysis
    • Organic Chemistry

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