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 KOHsolutions. Passive films are formed on the surface of anodically polarized, pure polycrystalline copper and a Cu-30Znalloy (α-brass), in aqueous 30% (7 M) and 45% (11.7 M) KOHelectrolyte 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 Cu2O, on the surface of Cu and Cu-30Znelectrodes in highly concentrated KOHsolutions, occurs at potentials above −400mVvs a standard hydrogen electrode (SHE). A porous passive layer is formed at potentials above −150mVvs SHE on pure Cu surfaces. In a 30%KOHsolution, this surface layer consists of Cu(OH)2, while in a 45%KOHsolution, the surface films comprise a Cu2O∕Cu(OH)2structure with the Cu2Oas the inner layer. The anodic polarization of Cu-30Zn(α-brass) leads to a complete dezincification of the surface, at potentials −350mVvs SHE, in both electrolyte solutions. Porous surface layers are formed on brass at these anodic potentials and have duplex structure, Cu2O∕Cu(OH)2, where the Cu(OH)2content increases with an increase in the KOHconcentration. At potentials −150mVvs SHE, the Cu(OH)2layer shows a preferential orientation of (020).