Anodic response of cystine at highly roughened gold electrodes in perchloric acid media

This manuscript compares the anodic response of the disulfide moiety of cys tine at the preanodized surfaces of polished and highly roughened Au rotate d disk electrodes (RDEs). The purpose of this study is the determination of the effect that roughening the electrode surface has on the effective numb er of electrons passed during cystine oxidation. The apparent number of ele ctrons transferred during oxidation of cystine is ca. 10 eq mol(-1) at the highly roughened Au RDE as compared to ca. 6 eq mol(-1) at the polished Au RDE. The transfer of 10 eq mol(-1) corresponds to complete oxidation of the disulfide moiety in cystine to two moles of cysteine sulfonic acid. The sp ecific area of the roughened surface is concluded to be 5-7 times larger th an that of the polished surface on the basis of comparisons of double-layer charging currents, current for anodic evolution of O-2, and data obtained by atomic force microscopy (AEM). Therefore, the larger value of n(app) for the roughened electrode is attributed to the electrocatalytic benefit of a n increased specific surface area acting within a response mechanism that i s believed to involve coadsorption of the reactant, cystine, and hydroxyl r adicals generated by anodic discharge of H2O2.