A Thin-Layer Electrochemical Cell for Infrared Spectroscopic Measurements of the Electrode/Electrolyte Interface

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Abstract
A thin-layer electrochemical cell which allows for the convenient measurement of infrared reflection-absorption spectra (IRRAS) of the electrode/electrolyte interphase has been designed and built. In order to minimize the thickness of the electrolyte in front of the electrode surface, one mounts the working electrode on the end of a piston so that it can be pressed against an infrared window. Infrared radiation is then reflected from the electrode surface via the infrared window without experiencing severe attenuation due to the electrolyte. Contaminants are minimized by the machining of both the cell body and piston from an inert fluorocarbon plastic. Calcium fluoride was chosen as the window material because of its transparency, its low refractive index, and its low solubility in aqueous electrolyte. The use of this cell in a Fourier transform infrared reflection-absorption spectrometer utilizing polarization modulation is described. The IRRAS spectra obtained from this cell have been analyzed with the use of the generalized Fresnel equations for stratified media. Some of the computational results for the water/silver electrode interphase are used to interpret the measured spectra of water near the electrode. The discussion includes infrared intensity distributions in aqueous media and their influence on the IRRAS measurement.