Measurement of the forward and back rate constants for electron transfer at the interface between two immiscible electrolyte solutions using scanning electrochemical microscopy (SECM): Theory and experiment |
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| Institution: | 1. Department of Physical Chemistry, Faculty of Chemistry, Warsaw University of Technology, Noakowskiego 3, 00-664 Warsaw, Poland;2. Thermodynamic Research Unit, School of Chemical Engineering, University of KwaZulu-Natal, Howard College Campus, King George V Avenue, Durban 4001, South Africa;1. Department of Physics, Science Faculty, Anadolu University, Eskişehir, 26470, Turkey;2. Department of Physics, Faculty of Sciences and Arts, Piri Reis University, 34940, İstanbul, Turkey;1. Department of Chemistry, Durham University, South Road, Durham DH1 3LE, UK;2. Chemical Crystallography, Department of Chemistry, Durham University, South Road, Durham DH1 3LE, UK;3. GlaxoSmithKline Pharmaceuticals, New Frontiers Science Park, Third Avenue, Harlow, Essex CM19 5AW, UK;1. Nanotechnology Research Laboratory, Department of Physics, Faculty of Science, University of Tabuk, Tabuk, Saudi Arabia;2. Department of Physics, Faculty of Education at Al-Mahweet, Sana’a University, Al-Mahweet, Yemen;3. Department of Physics, Faculty of Science, University of Jeddah, Jeddah, Saudi Arabia |
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| Abstract: | A new numerical model is developed for the scanning electrochemical microscopy (SECM) feedback mode for reversible electron transfer (ET) processes at the interface between two immiscible electrolyte solutions (ITIES). Results from this model were compared with data obtained using an earlier SECM feedback model in which the back reaction was not considered, to identify when the latter will be important. The dependence of the ET rate constant for the oxidation of 7,7,8,8-tetracyanoquinodimethane radical anion (TCNQ −) in 1,2-dichloroethane (DCE) by aqueous ferricyanide on the interfacial potential drop (Δwoφ) was studied using SECM. The Δwoφ value was varied by changing the concentration of NaClO4 in the aqueous phase while a fixed concentration of organic electrolyte, tetra-n-hexylammonium perchlorate, was used in the DCE phase. The results obtained were compared to earlier published studies on the forward reaction between TCNQ in DCE and aqueous ferrocyanide. Both the forward and back ET rate constants were found to depend strongly on the interfacial potential drop, with measured ET coefficients in the region of 0.5–0.6. A similar ET rate constant was observed at zero driving force for both the forward and back reactions. These experimental results suggest that the Butler–Volmer model applies to ET at the ITIES, when the driving force for the reaction is low, and under conditions of relatively high ionic strength in both the aqueous and organic phases. |
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