XANES for solid-liquid interface
The idea of using liquid cells for various vacuum-based techniques is not a recent development. In the soft X-ray absorption spectroscopy (sXAS) community, this strategy has been explored extensively and utilized to study various ambient condition liquids. However, most of the reported experiments focused on X-ray fluorescence measurements, where the X-ray photons emitted after the relaxation of the core-holes are collected and analyzed. Because the mean free paths (MFP) of soft X-ray photons in liquids or solids are of the order of hundreds of nanometers or even micrometers, the information provided by fluorescence spectra is essentially bulk-sensitive. As well as fluorescence photons, the relaxation of core-holes also results in the emission of Auger and secondary electrons whose IMFP are typically of the order of 1 nm.
Recently, our group demonstrated that by using a specially designed liquid cell and collecting these secondary electrons, electrode/electrolyte interfaces can be characterized in situ and operando inside a regular XAS chamber.
Here a 50-200 nm Si3N4 membrane serves as an X-ray transparent window, which also separates the UHV environment of the chamber from the ambient environment inside the liquid cell. The materials of interest are deposited on the flat side of the Si3N4 membrane, which functions as both working electrode and secondary electron current collector.
For more details, please see the published work:
- Velasco-Velez, J.-J.; Wu, C. H.; Pascal, T. A.; Wan, L. F.; Guo, J.; Prendergast, D.; Salmeron, M., The structure of interfacial water on gold electrodes studied by x-ray absorption spectroscopy. Science 2014, 346 , 831-834. doi: 10.1126/science.1259437
- Wu, C. H.; Weatherup, R. S.; Salmeron, M. B., Probing electrode/electrolyte interfaces in situ by X-ray spectroscopies: old methods, new tricks. Phys. Chem. Chem. Phys. 2015, 17 (45), 30229-30239.
- Weatherup, Robert; Wu, Chenghao; Escudero, Carlos; Perez-Dieste, Virginia; Salmeron, Miquel., Environment-Dependent Radiation Damage in Atmospheric Pressure X-ray Spectroscopy. J. Phys. Chem. B, 2017, 122, 737–744. DOI: 10.1021/acs.jpcb.7b06397
- Cheng Hao Wu, Tod A. Pascal, Artem Baskin, Huixin Wang, Hai-Tao Fang, Yi-Sheng Liu, Jinghua Guo, David Prendergast, and Miquel B. Salmeron. Molecular scale structure of electrode-electrolyte interfaces: the case of platinum in aqueous sulfuric acid. J. Am. Chem. Soc. , 2018, 140 (47), pp 16237–16244. DOI: 10.1021/jacs.8b09743