ИСТИНА

The dispute about the exact and correct mechanism of the electron transfer (ET) reactions at liquid-liquid interfaces (LLIs) has lasted for decades. In early days, these reactions were thought to be truly heterogeneous ET, as suggested by Samec et al..[1] Redox couples, namely K3/4[Fe(CN)6] in water and ferrocene (Fc+/0) in the organic phase, supposed to react only at the interface where electron transfer reactions occurred. Then, it was postulated by Kihara et al.,[2] Osakai et al.[3] and Katano et al.[4] that one of the reactant can, in fact, partition to the adjoint phase. Thus, it opened a new page of a homogenous ET mechanism associated with ion transfer reactions. In latter case, the measured current was not always due to a heterogeneous ET but rather due to the preceding or following ion transfer reaction. However, during long time contradicted data has been accumulated, which did not help to resolve the question about the correct mechanism of ET at LLIs. We address the present work to revisit this topic. We summarized our experience in electrochemical studies of redox reaction at LLIs, nanofilm preparation and redox catalysis at LLIs [5,6] and apply a finite element simulation approach to analyze recorded cyclic voltammograms (CVs). CVs were obtained at water-trifluorotoluene interface with the same redox couples, as used before, K3/4Fe(CN)6 and Fc+/0. Also, we showed how electron transfer pathways may alter after addition of an adsorbed gold nanoparticle film, improving the kinetics of the interfacial reactions. The current simulation results indicated that the electron transfer between Fc0 in the organic phase and K3Fe(CN)6 in the aqueous phase took place by the potential independent homogeneous reaction on the aqueous side of the cell. In this case, the observed potential dependence of the current stemmed from the concomitant ion transfer reaction of ferrocenium (Fc+). In the presence of the interfacial gold nanofilm the electron transfer took place by a bipolar mechanism where the electrons were shuttled through the metallic nanofilm. As the conclusion, this work showed that a more relevant question to ask is: Can the electron transfer reaction be considered as independent of the applied potential? The answer is most likely: Yes. References: [1] Z. Samec, V. Mareček, J. Weber, Detection of an electron transfer across the interface between two immiscible electrolyte solutions by cyclic voltammetry with four-electrode system, J. Electroanal. Chem. Interfacial Electrochem. 96 (1979) 245–247. doi:10.1016/S0022-0728(79)80382-4. [2] S. Kihara, M. Suzuki, K. Maeda, K. Ogura, M. Matsui, Z. Yoshida, The electron transfer at a liquid / liquid interface studied by current-scan polarography at the electrolyte dropping electrode, J. Electroanal. Chem. Interfacial Electrochem. 271 (1989) 107–125. doi:10.1016/0022-0728(89)80068-3. [3] H. Hotta, S. Ichikawa, T. Sugihara, T. Osakai, Clarification of the Mechanism of Interfacial Electron-Transfer Reaction between Ferrocene and Hexacyanoferrate(III) by Digital Simulation of Cyclic Voltammograms, J. Phys. Chem. B. 107 (2003) 9717–9725. doi:10.1021/jp035058p. [4] H. TATSUMI, H. KATANO, Cyclic Voltammetry of the Electron Transfer Reaction between Bis(cyclopentadienyl)iron in 1,2-Dichloroethane and Hexacyanoferrate in Water, Anal. Sci. 23 (2007) 589–591. doi:10.2116/analsci.23.589. [5] E. Smirnov, P. Peljo, M.D. Scanlon, H.H. Girault, Interfacial Redox Catalysis on Gold Nanofilms at Soft Interfaces, ACS Nano. 9 (2015) 6565–6575. doi:10.1021/acsnano.5b02547. [6] E. Smirnov, P. Peljo, M.D. Scanlon, H.H. Girault, Gold Nanofilm Redox Catalysis for Oxygen Reduction at Soft Interfaces, Electrochim. Acta. (2015). doi:10.1016/j.electacta.2015.10.104.