On the Electrochemical Behavior and Passivation of Copper and Brass (Cu70∕Zn30) Electrodes in Concentrated Aqueous KOH Solutions

We report on the study of the electrochemical behavior of copper and brass electrodes in concentrated aqueous solutions. Passive films are formed on the surface of anodically polarized, pure polycrystalline copper and a alloy (α-brass), in aqueous 30% (7 M) and 45% (11.7 M) electrolyte solutions, at two characteristic potentials (corresponding to the two major anodic peaks in the voltammograms of these systems). The structure and composition of the films were determined by ex situ X-ray diffraction (XRD), in situ and ex situ micro-Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and atomic force microscopy (AFM). The formation of crystalline cubic , on the surface of Cu and electrodes in highly concentrated solutions, occurs at potentials above vs a standard hydrogen electrode (SHE). A porous passive layer is formed at potentials above vs SHE on pure Cu surfaces. In a solution, this surface layer consists of , while in a solution, the surface films comprise a structure with the as the inner layer. The anodic polarization of (α-brass) leads to a complete dezincification of the surface, at potentials vs SHE, in both electrolyte solutions. Porous surface layers are formed on brass at these anodic potentials and have duplex structure, , where the content increases with an increase in the concentration. At potentials vs SHE, the layer shows a preferential orientation of (020).