| Institution: | 1. Inorganic Chemistry and Center for Nanointegration Duisburg-Essen (CeNIDE), University of Duisburg-Essen, Universitätsstr. 5–7, 45117 Essen, Germany
These authors contributed equally to this work.;2. Institute of Energy and Climate Research, Electrochemical Process Engineering (IEK-3), Forschungszentrum Jülich GmbH, 52425 Jülich, Germany;3. Interdisciplinary Center for Analytics on the Nanoscale (ICAN) and Center for Nanointegration Duisburg-Essen (CENIDE), University of, Duisburg-Essen, Carl-Benz-Strasse 199, 47057 Duisburg, Germany;4. Ernst Ruska-Centre for Microscopy and Spectroscopy with Electrons, Forschungszentrum Jülich GmbH, 52425 Jülich, Germany;5. Institute of Energy and Climate Research, Fundamental Electrochemistry (IEK-9), Forschungszentrum Jülich GmbH, 52425 Jülich, Germany;6. Department of Materials Science and Engineering, Kyushu University, 744, Motooka, Nishi, Fukuoka, 819-0395 Japan;7. Inorganic Chemistry and Center for Nanointegration Duisburg-Essen (CeNIDE), University of Duisburg-Essen, Universitätsstr. 5–7, 45117 Essen, Germany |
| 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. |
