Abstract: This article describes the capabilities of coupled UHV-electrochemistry as a means to obtain the microscopic information of the electrode-solution interface. It presents the experimental aspects for sample preparation and surface analytical techniques and some selected studies of the recent results with single-crystal electrode surfaces; the phase transition for the reconstructed Au(100)-hex and Pt(100)-hex electrodes in the electrochemical cell and the structural study of the epitaxial growth of Pt on Ru(0001) and Ru(1010) surfaces as well as the growth of RuO2(100) on Ru(0001).

Key words: Electrochemistry, Electrode emersion, Electron diffraction, Structural transformation