Cu(110) Surface in Hydrochloric Acid Solution: Potential Dependent Chloride Adsorption and Surface Restructuring

Using cyclic voltammetry (CV), reflectance anisotropy spectroscopy (RAS), and in situ electrochemical scanning tunneling microscopy (EC-STM), we have studied the structure and structural transitions at a Cu(110) electrode surface in 10 mM HCl solution as a function of the applied electrode potential. While at potentials lower than −550 mV vs Ag/AgCl the in situ STM images reveal the adsorbate-free, unreconstructed structure of the Cu(110) surface, at increasing potential ≥ −550 mV chloride adsorption, as indicated by CV, leads first to the formation of grooves followed by the growth of added stripes. Both are aligned in the [001] direction as shown by EC-STM—and supported by ex situ low energy electron diffraction (LEED)—and are the result of a severe but fully reversible restructuring of the surface. This faceting is accompanied by an optical anisotropy peak in RAS centered at about 500 nm (2.48 eV), having a maximum when the linearly polarized light is aligned along the [11̅0] direction, i.e., perpendicular to the stripes detected with in situ STM under the same conditions. By cycling the electrode potential through a full cyclic voltammogram and monitoring simultaneously the RAS signal we obtain a hysteresis-like curve which supports a two-step kinetics of the restructuring process in agreement with the CV and STM data. The investigations demonstrate the power of combined RAS and in situ STM measurements to shine light on potential-driven processes at metal–electrolyte interfaces.