Structure of the Electrochemical Interface: Ag(hkl) in an Alkaline Electrolyte

The structure of the electrochemical double layer at the interface between Ag(hkl) electrodes and 0.1 M NaOH electrolyte has been probed using in situ surface X-ray diffraction (SXRD) measurements. The three low-index Ag(hkl) surfaces were prepared and characterized under ultra-high vacuum (UHV) conditions before being transferred into the electrochemical environment. Crystal truncation rod (CTR) measurements were made at negative potentials (just negative of the pzc), where there is no specific adsorption onto the electrode surfaces, and at more positive potentials, where hydroxide species is specifically adsorbed. The measurements quantify the relaxation at the metal electrode surfaces and, through the specular CTR, give information about layering on the electrolyte side of the interface. Strong layering effects are observed on the Ag(111) and Ag(110) surfaces, whereas on Ag(001) the layering is much weaker and we attribute this to the symmetry mismatch to the adsorbing water network. The effect of saturating the electrolyte with carbon monoxide (CO) was also examined, and structural changes were only observed on the Ag(110) surface. The changes observed suggest a stabilization of a coadsorbed CO-OH adlayer due to charge redistribution that delays the onset of CO oxidation.