Thermodynamic and electro-kinetic analyses of direct electron transfer (DET) and mediator-involved electron transfer (ME
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FEATURE ARTICLE
Thermodynamic and electro-kinetic analyses of direct electron transfer (DET) and mediator-involved electron transfer (MET) with the help of a redox electron mediator Su-Il Pyun 1 Received: 28 March 2020 / Revised: 17 July 2020 / Accepted: 21 July 2020 # Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract In this report, we conceptually distinguish direct electron transfer (DET) from mediator-involved (mediated) electron transfer (MET) in a glucose/oxygen-based fuel cell (FC) using an electrode potential/Fermi energy diagram. The anodic and cathodic overvoltages deviating from the equilibrium potential (the Fermi energy of redox electrons) were taken into account for the organic/inorganic redox couple and the mental experiments were performed during the trip of redox electrons through the interface between the anodic/cathodic organic/inorganic active mass and electrodes to propose electron transfer pathway. The proposed schema (inequality (MET) and equality in Fermi energy (DET)) should be experimentally corroborated by measurement of the electromotive force (emf). The MET is of technological significance in the presence of an electron mediator of the redox couple, despite a slightly narrower emf estimated between two electrodes by roughly 1 to 2 mV at most than the DET, in view of the thermodynamic and electro-kinetic viewpoints. Keywords Oxygen reduction . Electron mediator . Reversible reaction . Spontaneous reaction . Gaseous oxygen . Direct electron transfer (DET) . Mediated electron transfer (MET) . Fermi energy (electrochemical potential) of redox electrons . Gibbs free energy (chemical potential) . Oxidant (oxidized species) . Reductant (reduced species) . Electron donor . Electron acceptor
Introduction It is well known from the literature [1–3] that the transfer of electrons from one phase (substrate or microbe) to another phase such as an electrode proceeds mainly by two mechanisms in a glucose-based fuel cell (FC). One is mediatorinvolved (mediated) electron transfer (MET) in the presence of an electron mediator of the redox couple, and the other is direct electron transfer (DET) in the absence of an electron mediator of the redox couple or in a mediator-less state. The thermodynamic and electro-kinetic analyses of MET and DET “An original communication” as a contribution to “the Fritz Scholz birthday Festschrift issue” * Su-Il Pyun [email protected] 1
Munji-Campus of Korea Advanced Institute of Science & Technology, Corrosion and Interfacial Electrochemistry Research Room, R101, Research Building, #193 Munji-Ro, Yuseong-Gu, Daejeon 305-701, Republic of Korea
need to be supplemented. In special cases, the electron transfer for a redox reaction through the electrical double-layer with simultaneous transfer of cations is called the charge transfer reaction (“die Ladungsdurchtrittsreaktion”) [4]. The charge transfer reaction is preceded by diffusion through the electrolytic solution at the interface between the cathode of FC and the solution as well as at corroding metal
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