Gajdek Dorotea, Olsson Pär A T, Blomberg Sara, Gustafson Johan, Carlsson Per-Anders, Haase Dörthe, Lundgren Edvin, Merte Lindsay R
Department of Materials Science and Applied Mathematics, Malmö University, SE-211 19 Malmö, Sweden.
NanoLund, Lund University, Box 118, SE-221 00 Lund, Sweden.
J Phys Chem C Nanomater Interfaces. 2022 Feb 24;126(7):3411-3418. doi: 10.1021/acs.jpcc.1c10284. Epub 2022 Feb 16.
We have used grazing incidence X-ray absorption fine structure spectroscopy at the cobalt K-edge to characterize monolayer CoO films on Pt(111) under ambient pressure exposure to CO and O, with the aim of identifying the Co phases present and their transformations under oxidizing and reducing conditions. X-ray absorption near edge structure (XANES) spectra show clear changes in the chemical state of Co, with the 2+ state predominant under CO exposure and the 3+ state predominant under O-rich conditions. Extended X-ray absorption fine structure spectroscopy (EXAFS) analysis shows that the CoO bilayer characterized in ultrahigh vacuum is not formed under the conditions used in this study. Instead, the spectra acquired at low temperatures suggest formation of cobalt hydroxide and oxyhydroxide. At higher temperatures, the spectra indicate dewetting of the film and suggest formation of bulklike CoO under oxidizing conditions. The experiments demonstrate the power of hard X-ray spectroscopy to probe the structures of well-defined oxide monolayers on metal single crystals under realistic catalytic conditions.
我们利用钴K边的掠入射X射线吸收精细结构光谱，对在环境压力下暴露于CO和O的Pt(111)上的单层CoO薄膜进行表征，目的是确定存在的Co相及其在氧化和还原条件下的转变。X射线吸收近边结构（XANES）光谱显示Co的化学状态有明显变化，在CO暴露下以2+状态为主，在富O条件下以3+状态为主。扩展X射线吸收精细结构光谱（EXAFS）分析表明，在本研究使用的条件下，在超高真空下表征的CoO双层并未形成。相反，在低温下采集的光谱表明形成了氢氧化钴和羟基氧化钴。在较高温度下，光谱表明薄膜发生去湿，并表明在氧化条件下形成块状CoO。这些实验证明了硬X射线光谱在实际催化条件下探测金属单晶上明确的氧化物单层结构的能力。
