Channel-Flow Cell for X-ray Absorption Spectroelectrochemistry

Abstract

X-ray absorption spectroscopy has the potential to provide valuable information not obtainable by other spectroscopic techniques on the structure of intermediates in electron-transfer reactions. Microfocused X-rays have been identified as powerful tools for probing the solution in the vicinity of the working electrode, and the design of an electrochemical flow cell suitable for such measurements is described. The flowing solution, found to be essential to remove any products of beam damage, is characterized by mapping X-ray absorption changes as a function of applied potential and position within the channel. [{Fe(η5-C5H5)(CO)(μ-SPh)}2], used as a model system, undergoes two reversible, one-electron oxidations giving rise to a shortening of the Fe−Fe distance and significant changes in X-ray absorption, making it an ideal compound for trial studies. Two-dimensional numerical modeling is used to rationalize the observed absorption changes and hence solution composition. Excellent agreement between calculated and observed changes in absorbance is found in the vicinity of the electrode although there are substantial differences where forced convection dominates mass transport. These experiments represent the first steps in demonstrating that the combination of microfocused X-rays with electrochemical flow cells has the potential to be a powerful technique for opening up new possibilities for studies of intermediates in electron-transfer reactions.

Homogeneously Catalyzed Electroreduction of Carbon Dioxide—Methods, Mechanisms, and Catalysts

“…With regard to operando spectroscopy, FTIR-SEC and UV–vis-SEC have been most widely used to study CO 2 -electroreduction mechanisms. The techniques for coupling of electrochemistry to Raman, , EPR, and X-ray spectroscopy , are in principle available and provide further potential for future studies in the field of CO 2 electroreduction.…”

Using XAS to monitor radiation damage in real time and post-analysis, and investigation of systematic errors of fluorescence XAS for Cu-bound amyloid-β

“…Frozen samples are used with low X-ray fluxes to control the effect of radiation damage. Electro-synthetic cells and flow cells have been used to obtain in situ XAFS of redox states of reactive species (Dewald et al, 1986;Milsmann et al, 2006;Wiltshire et al, 2009;Best et al, 2016). The collection of a sufficiently large number of quality measurements of samples of in situ electrochemically generated states for a considerable duration is a major challenge.…”

XAS spectroelectrochemistry: reliable measurement of X-ray absorption spectra from redox manipulated solutions at room temperature

“…Several approaches have been reported that allow in situ XAS measurements from samples in controlled redox states and these use methodologies that range from bulk electrosynthesis cells (typically of volume 1-10 ml) with largesurface-area electrodes (Dewald et al, 1986;Bae et al, 2001;Levina et al, 2004;Hennig et al, 2005;Milsmann et al, 2006;Takao et al, 2010) to channel-flow cells (Wiltshire et al, 2009) and cells optimized for the study of electrode transformations (McBreen et al, 1987;Nakanishi et al, 2014). While bulk electrosynthesis cells have been used to obtain XAS spectra, the long electrosynthesis period (typically > 10 min) makes them impracticable for the study of short-lived reactive species, or for samples, such as metalloproteins, that are only available in small quantities.…”

“…While bulk electrosynthesis cells have been used to obtain XAS spectra, the long electrosynthesis period (typically > 10 min) makes them impracticable for the study of short-lived reactive species, or for samples, such as metalloproteins, that are only available in small quantities. The channel-flow cell of Wiltshire and co-workers presents a narrow cross-section ($ 1 mm 2 ) and a flow rate of 200 mL h À1 would correspond to a residence time of the sample of $ 1s in a 50 mm focused beam (Wiltshire et al, 2009). However, the suitability of this approach is limited by the comparatively small extent of electrosynthesis able to be obtained under working conditions (5% conversion when using a 400 mm-wide ribbon electrode).…”