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Nanoscopic Porous Iridium/Iridium Dioxide Superstructures (15 nm): Synthesis and Thermal Conversion by In Situ Transmission Electron Microscopy
Author(s) -
Pappert Kevin,
Loza Kateryna,
Shviro Meital,
Hagemann Ulrich,
Heggen Marc,
DuninBorkowski Rafal E.,
Schierholz Roland,
Maeda Takuya,
Kaneko Kenji,
Epple Matthias
Publication year - 2019
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201901623
Subject(s) - iridium , materials science , transmission electron microscopy , chemical engineering , sodium borohydride , nanoparticle , water splitting , porosity , hydrogen , particle (ecology) , nanotechnology , catalysis , chemistry , photocatalysis , composite material , organic chemistry , oceanography , geology , engineering
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.