Reksten Anita Hamar, Russell Andrea E, Richardson Peter W, Thompson Stephen J, Mathisen Karina, Seland Frode, Sunde Svein
Department of Materials Science and Engineering, Norwegian University of Science and Technology (NTNU), NO-7491, Trondheim, Norway.
Phys Chem Chem Phys. 2020 Sep 14;22(34):18868-18881. doi: 10.1039/d0cp00217h. Epub 2020 Apr 14.
Iridium oxide powders with a surface area of more than 1 m g (4 m g from the H-UPD charge) and iridium-oxide crystallites less than 10 nm across were synthesized by heat treating gels formed from citric acid, ethylene glycol and dihydrogen hexachloroiridate(iv) in air. The characteristics of the resulting material was found to be strongly dependent on the heat-treatment step in the synthesis. A single heat-treatment of the gel resulted in a material with a substantial fraction of elemental iridium metal, i.e. iridium in oxidation state zero (Ir). Post-synthesis modification of the powder by potential cycling resulted in oxidation peaks consistent with the conversion of the metal phase to iridium oxide. Linear combination of the near-edge part of the X-ray absorption data (X-ray absorption near-edge spectroscopy, XANES) collected in situ during potential cycling and an analysis of the extended X-ray fine-structure (EXAFS) part of the spectrum showed that the overall metal fraction was not significantly affected by the cycling. The oxidation of the metal phase is therefore limited to a thin layer of oxide at the metal surface, and a significant part of the iridium is left inactive. A modification of the heat treatment procedure of the sample resulted in iridium oxide containing only insignificant amounts of elemental iridium metal.
通过在空气中热处理由柠檬酸、乙二醇和六氯铱酸（IV）二氢形成的凝胶，合成了表面积大于1平方米/克（氢欠电位沉积电荷为4平方米/克）且氧化铱微晶尺寸小于10纳米的氧化铱粉末。发现所得材料的特性强烈依赖于合成中的热处理步骤。对凝胶进行单次热处理会得到一种含有大量元素铱金属（即氧化态为零的铱，Ir）的材料。通过电位循环对粉末进行合成后改性，会产生与金属相转变为氧化铱一致的氧化峰。在电位循环过程中原位收集的X射线吸收数据（X射线吸收近边光谱，XANES）的近边部分的线性组合以及光谱扩展X射线精细结构（EXAFS）部分的分析表明，循环对整体金属含量没有显著影响。因此，金属相的氧化仅限于金属表面的一层薄氧化物，并且大部分铱保持无活性。对样品热处理程序的修改导致氧化铱仅含有极少量的元素铱金属。
