Interface between electrode and electrolyte

The electron transfer (ET) at the interface between electrode and electrolyte is central to an electrode reaction. Electrons pass through the interface. Macroscopically we observe a current i. 

Impedance spectroscopy a single interface. Draw the equivalent circuits for the following electrode/electrolyte interfaces, then derive their impedance expression and explain what their Cole-Cole plot will look like (a) An ideally polarizable interface between electrode and electrolyte, (b) An ideally nonpolarizable interface between electrode and electrolyte, (c) A real-life electrode/... 

Figure 3.2.1 Schematicpicture of the anode interface between electrode and electrolyte at which the OER takes place.

Precisely symmetrical models of aqueous electrode interfaces are often shown for educational purposes. Polar water molecules and positive ions are assembled in a repetitive array. In reality the array would be interrupted by impurities and irregularities, all thermally agitated. The precise achievement of a potential difference V , corresponding to Nernst s equation (4.1), would require microscopically uniform conditions at the interface between electrode and electrolyte, so as to avoid local variations of potential difference and circulating currents in the electrode. 

For the oxidation reaction Ag - e Ag, it is assumed that an ion crosses the interface between electrode and electrolyte. As in the precee-dingly described case, an activation energy, depending on the electrode potential, is necessary and the current-potential relation is given by the Butler Volmer relation ... 

Figure 6.19. In the Daniell cell the electrode pair Zn-Cu is in conductive electrolytic contact through a porous wall thus, the same electric potential in both of the electrolytes is ensured. Since the potential difference over the interface between electrode and electrolyte is different for the Zn electrode and the Cu electrode, an electrochemical potential difference ofV os. 1.10 volt arises between the electrodes in the unloaded cell.

Figure 6.25. Physical significance of a galvanic cell for a cell with an active Zn-anode and an active Cu cathode. It shall be noted that electrochemical cell reactions are always connected with the interface between electrode and electrolyte.

Molecular-level SOFC models aim to understand (i) the kinetics of the reaction at the interface between electrode and electrolyte, (ii) the conduction process in the electrolyte, and (iii) the conduction process in the electrodes. Catalytic activity at TPB, activation energy for oxygen ion transport, and surface exchange current are application examples for such models. 

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