Atomic and molecular scale structural analysis of electrode/electrolyte interfaces

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The aim of this research project was to characterize the electrochemical interface at atomic and molecular scales in order to get deeper insight into the interface and reactions take place there. Surface-enhanced infrared absorption spectroscopy (SEIRAS) developed in our laboratory and scanning tunneling microscopy (STM) coupled with conventional electrochemical techniques were used to characterize the interface. Special attention was focused to dynamic behavior of the interface and reactions. A novel infrared spectroscopy technique that enables monitoring very fact electrode dynamics and kinetic have been developed for this purpose. The results obtained are summarized as follows :(1) Double-layer structure. It has long been assumed that water molecules at the electrochemical interface are isolated from the hydrogen-bonded network in the bulk and reorient with applied potential. This assumption was verified for the first time by using SEIRAS.The orientations deduced are different from … More those assumed in classical models and in accord with recent molecular dynamics simulations. We also found that the double-layer structure is largely changed by the coadsorption of supporting anions.(2)Electrode dynamics. We have succeeded for the first time in infrared and electrochemical simultaneous measurements, which enabled detailed investigation of electrode dynamics. Change in double-layer structure, charge-transfer between the electrode and adsorbed molecules, and several reactions were investigated.(3) Adsorption and desorption of molecules at the interface. Adstructures of a number of molecules on gold single-crystal electrodes were determined. The change in molecular structure by adsorption, two-dimensional phase transition in adlayers, physisorption-chemisorption transition, and potential-dependent reorientation were found for several molecules.(4) Correlation between the structure and functions of rnodified electrodes. Surface pKa values of self-assembled monolayers (SAMs) of aromatic thiols on gold electrodes were determined by SEIRAS.The acid-base property of SAMs was found to greatly influence the functions of the modified electrodes, such as the promotion activity toward heterogeneous electron-transfer between the electrode and cytochrome c. Less