Development and application of in situ/operando soft X-ray transmission cells to aqueous solutions and catalytic and electrochemical reactions

In this review, we have demonstrated several applications of newly-developed in situ/operando liquid flow cells for the transmission XAS (X-ray absorption spectroscopy) measurement in the soft X-ray undulator beamline BL3U dedicated to the chemical application of UVSOR-III Synchrotron. The liquid layer is sandwiched between two thin membranes and its thickness is easily controllable to optimize the absorbance. Liquid samples are exchangeable in situ. Molecular spectra in liquid and gas phases are simultaneously measureable and it makes the energy calibration rather easy. By using a standard version of the liquid cells, we have investigated local structures of several aqueous solutions of alkali halides, methanol, pyridine, and acetonitrile. To observe catalytic and electrochemical reactions under realistic conditions, we have developed in situ/operando versions of the liquid cells. We have investigated local structures of the catalytic hydration reaction of cyanopyrazine under the temperature control and the electrochemical reaction of aqueous iron sulfate solutions using the built-in electrodes under the same scan rate as in cyclic voltammetry. We have discussed future perspectives of our in situ/operando liquid flow cells applied to XAS in the soft X-ray region.