An unusual electron-transfer behavior of ferrocene in aqueous microemulsion systems

The electrochemical behavior of ferrocene in an aqueous microemulsion (pentan-1-ol/sodium dodecyl sulfate (SDS)/aq. H₂SO₄) has been studied using an ultramicroelectrode. Contrary to the generally expected reversible peak, the experiments show the presence of a second oxidation peak during the reverse scan at low scan rates where the peak corresponding to ferricinium ion reduction is nearly absent along with the unanticipated appearance of a current dip. These observations are rationalized using a novel type of coupling between heterogeneous (electrochemical) and homogeneous (chemical) electron transfer processes. The composition of the medium, especially the acid concentration, affects the electron transfer of the solubilized probe and there exists a threshold acid concentration for achieving maximum anodic peak current.