Kinetics of Heterogeneous Electron Transfer Reactions at the Externally Polarized Water/<i>o-</i>Nitrophenyl Octyl Ether Interface

Abstract

The heterogeneous electron transfer (ET) reactions between dimethylferrocenium (DiMFc+) or ferrocenium (Fc+) produced in situ in o-nitrophenyl octyl ether (NPOE) and hexacyanoferrite [Fe(CN)64−] in aqueous phase have been investigated by scanning electrochemical microscopy (SECM). The potential difference across the water/NPOE (W/NPOE) interface was controlled externally to maintain a certain driving force for the ET reactions. The standard kinetic rate constants (k120) for the above bimolecular ET reactions were measured to be 0.075 and 0.050 cm s−1 M−1 when DiMFc and Fc were employed as the respective organic reactants. The transfer coefficients (α) were calculated to be 1.09 and 1.62, respectively. Those abnormal values of α were analyzed and ascribed to the Frumkin effect (or diffuse layer effect) at both sides of the interfaces. Some of the previous reports are summarized and also analyzed based on the Frumkin effect. The possible effect of ion transfer on the ET process is discussed in detail.