Infrared Spectroscopic imaging of reactions at solid-liquid interfaces

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This project aimed to image chemical reactions that propagate two dimensionally over solid surfaces in solution by using infrared spectroscopy. Different from conventional optical microscope, two dimensional distributions of chemical species involved in the reactions can be imaged by plotting the intensity or frequency of a molecular vibration characteristic to each species. To realize the IR imaging, a 64 x 64 multi-channel MCT detector (Focal Plane Analyzer, FPA) was used. The target we have interested in is fast reactions of adsorbed monolayers and an experimental difficulty of the present approach is the very low IR absorption. To overcome this problem, surface-enhanced infrared absorption spectroscopy (SEIRAS) developed in this laboratory was couple. After great efforts, we have succeeded in imaging the spatial distribution of CO adsorbed on Pt electrodes (including patterned electrodes) and demonstrated the usefulness of this approach. However, we have not yet succeeded in monitoring spatially and temporally oscillating patterns that are expected to be formed under galvanostatic or potentiostatic electro-oxidation of formic acid due to the low signal-to-noise ratio of the image and the slow data transfer rate from the FT-IR spectrometer to the controlling computer (the data size of one image is a few GB). This problem will be removed in future by modifying the electronics of the spectrometer.In parallel, we investigated the mechanisms of several catalytic reactions at the electrochemical interface, such as hydrogen evolution reaction on Pt and Ag, electro-oxidation of small organic molecules (CO, methanol, formaldehyde, formic acid, and dimethyl eter). The most notable achievement in this series of study is that electrooxidation of small organic molecules occurs through formate species adsorbed on the surface. The mechanism of each reaction was examined in detail by IR spectroscopy.