A voltammetric investigation of ethylamine oxidation at Ag, Au and Au80Ag20 electrodes in alkaline media

A voltammetric comparison is presented for the anodic response of ethylamin e 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 res ponse mechanisms at binary alloy electrodes that are not existent at electr odes made from the pure component metals. The primary anodic response for e thylamine at the Au RDE corresponds to oxidative desorption of reactant con comitantly with formation of surface oxide (AuO) during the positive potent ial scan. For the Ag RDE, ethylamine enhances the anodic wave corresponding to formation of surface oxide (Ag2O) during the positive scan; however, th e majority of this current enhancement is attributed to chemical stripping of Ag2O by the amine with formation of additional surface oxide. Evidence f or this anodic stripping mechanism includes rapid roughening of the electro de surface. The response for ethylamine obtained at the Au80Ag20 RDE is con cluded to correspond to the superposition of the response characteristic of Au electrodes with a response at the Ag sites that is dramatically differe nt from the response observed at the pure Ag RDE. Data obtained by X-ray ph otoelectron 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 thereb y preventing their dissolution from the Au80Ag20 electrode. The voltammetri c 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 mec hanisms to explain the ethylamine response at the Ag sites in the alloy ele ctrode.