A Voltammetric Investigation of Ethylamine Oxidation at Ag, Au and Au 80 Ag 20 Electrodes in Alkaline Media

Abstract

A voltammetric comparison is presented for the anodic response of ethylamine at Ag, Au and Au80Ag20 rotated disk electrodes (RDEs) in carbonate buffer (pH 11.2). This study is part of a systematic search for unique anodic response mechanisms at binary alloy electrodes that are not existent at electrodes made from the pure component metals. The primary anodic response for ethylamine at the Au RDE corresponds to oxidative desorption of reactant concomitantly with formation of surface oxide (AuO) during the positive potential scan. For the Ag RDE, ethylamine enhances the anodic wave corresponding to formation of surface oxide (Ag2O) during the positive scan; however, the majority of this current enhancement is attributed to chemical stripping of Ag2O by the amine with formation of additional surface oxide. Evidence for this anodic stripping mechanism includes rapid roughening of the electrode surface. The response for ethylamine obtained at the Au80Ag20 RDE is concluded to correspond to the superposition of the response characteristic of Au electrodes with a response at the Ag sites that is dramatically different from the response observed at the pure Ag RDE. Data obtained by X-ray photoelectron spectroscopy (XPS) indicate that the surface composition of the Au80Ag20 electrode does not change as a result of exposure to ethylamine. Therefore, it is apparent that the Au matrix stabilizes the Ag atoms thereby preventing their dissolution from the Au80Ag20 electrode. The voltammetric response for ethylamine at the Ag sites observed during the positive scan is independent of rotational velocity; however, for the negative scan, an inverse Levich behavior is observed. Consideration is given to possible mechanisms to explain the ethylamine response at the Ag sites in the alloy electrode.