Pappert Kevin, Loza Kateryna, Shviro Meital, Hagemann Ulrich, Heggen Marc, Dunin-Borkowski Rafal E, Schierholz Roland, Maeda Takuya, Kaneko Kenji, Epple Matthias
Inorganic Chemistry and Center for Nanointegration Duisburg-Essen (CeNIDE), University of Duisburg-Essen, Universitätsstr. 5-7, 45117, Essen, Germany.
Institute of Energy and Climate Research, Electrochemical Process Engineering (IEK-3), Forschungszentrum Jülich GmbH, 52425, Jülich, Germany.
Chemistry. 2019 Aug 22;25(47):11048-11057. doi: 10.1002/chem.201901623. Epub 2019 Aug 1.
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.
通过在水中用柠檬酸钠/硼氢化钠还原六氯铱酸钠（+IV），制备了直径约15 nm的多孔颗粒超结构，其由铱和二氧化铱的超小纳米颗粒组成。水分散性多孔颗粒含有约20 wt%的聚（N-乙烯基吡咯烷酮）（PVP），添加它是为了实现胶体稳定化。高分辨率透射电子显微镜证实每个多孔超结构中都存在铱和二氧化铱初级颗粒（1-2 nm）。电子断层扫描显示了内部孔隙率（≈58 vol%）。在氧气、氮气、氩气/氢气（均为1 bar）和真空环境下，在高达1000 °C的原位透射电子显微镜观察表明，多孔颗粒在加热时会发生烧结并随后压实，这个过程在约250 °C开始，在约800 °C完成。最后，在所有四种环境下都获得了结晶良好的二氧化铱。由于孔隙烧结和内表面积损失，所制备的多孔超结构在电化学水分解（析氧反应；OER）中的催化活性在加热后大幅降低。
