Channel-Flow Cell for X-ray Absorption Spectroelectrochemistry

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(eta(5)-C5H5)(CO)(mu-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.