Surface X-ray diffraction studies of the electrochemical interface

Abstract

This thesis describes the application of in-situ surface X-ray diffraction (SXRD) experiments to the study of electrochemical interfaces. Measurements performed at synchrotron radiation facilities are used to provide in-sight into the surface structure of electrodes and the electrochemical double layer. The impact of structural changes on electrochemical reactivity, and likewise the impact of electrochemical processes on electrode structure are discussed. Measurements of the Au (111) reconstruction in alkaline solution indicate that the presence of CO causes the partial lifting of the reconstruction; it is suggested that this leads to an increase in defects and this is the underlying reason for CO promoted gold catalysis. In-situ SXRD measurements with a non-aqueous electrolyte are presented, representing a technological advance in the study of electrochemical interfaces. Crystal truncation rods (CTRs) measured at the Pt (111) / non-aqueous acetonitrile interface are used to determine the structure of both the electrode surface and the electrolyte close to the interface. The results indicate that acetonitrile undergoes a potential dependant reorientation but, in the presence of molecular oxygen, the acetonitrile molecules close to the electrode are dissociated and therefore cannot reorient. Measurements of CTRs at the Pt (111) / electrolyte interface for several aqueous electrolytes are combined with CTRs measured in non-aqueous acetonitrile to explore the dependence of surface relaxation on adsorption. Fits to CTRs are also used to determine the double layer structure at aqueous Pt (111) / acetonitrile interfaces and how it varies with acetonitrile concentration. The results indicate that the acetonitrile adsorption increases with concentration and that the double layer region compresses.