Electrode-electrolyte polarized

However, these classical models neglect various aspects of the interface, such as image charges, surface polarization, and interactions between the excess charges and the water dipoles. Therefore, the widths of the electrode/electrolyte interfaces are usually underestimated. In addition, the ion distribution within the interfaces is not fixed, which for short times might lead to much stronger electric helds near the electrodes. 

Kunimatsu K, Seki H, Golden WG, Gordon JG II, Philpott MR. 1985b. Electrode/electrolyte interface study using polarization modulated FTIR reflection-adsorption spectroscopy. Surf Sci 158 596-608. 

Schematic representation of the experimental setup for an in situ IR study of the electrode-electrolyte interface is given in Fig. 1.5. From the radiation leaving the IR source only, the p-polarized light is used for the reflection-absorption experiment in...

The combination of surface enhanced Raman scattering (SERS) and infrared reflection absorption spectroscopy (IRRAS) provides an effective in-situ approach for studying the electrode-electrolyte interface. The extreme sensitivity to surface species of SERS is well known. By using polarization modulation of the infrared beam for IRRAS, the complete band shape is obtained without modulating the electrode potential. 

The polarized Electrode-Electrolyte and the reversible Solid-Electrolyte Interface... 

Comparison between the polarized electrode-electrolyte interface and the reversible (Al203) oxide-electrolyte interface. Surface tension (interfacial) tension, charge density and differential capacity, respectively, are plotted as a function of the rational potential vy (at pzc vy is set = 0) in the case of Hg and as a function of ApH (pH-pH ) in the case of Al203 (pH = pHpzc when a = 0). 

Activation polarization arises from kinetics hindrances of the charge-transfer reaction taking place at the electrode/electrolyte interface. This type of kinetics is best understood using the absolute reaction rate theory or the transition state theory. In these treatments, the path followed by the reaction proceeds by a route involving an activated complex, where the rate-limiting step is the dissociation of the activated complex. The rate, current flow, i (/ = HA and lo = lolA, where A is the electrode surface area), of a charge-transfer-controlled battery reaction can be given by the Butler—Volmer equation as... 

Ohmic polarization arises from the resistance of the electrolyte, the conductive diluent, and materials of construction of the electrodes, current collectors, terminals, and contact between particles of the active mass and conductive diluent or from a resistive film on the surface of the electrode. Ohmic polarization appears and disappears instantaneously (<10 s) when current flows and ceases. Under the effect of ohmic resistance, R, there is a linear Ohm s Law relationship between /and rj. 

As the redox reactions proceed, the availability of the active species at the electrode/electrolyte interface changes. Concentration polarization arises from limited mass transport capabilities, for example, limited diffusion of active species to and from the electrode surface to replace the reacted material to sustain the reaction. Diffusion limitations are relatively slow, and the buildup and decay take >10 s to appear. For limited diffusion the electrolyte solution, the concentration polarization, can be expressed as... 

Figure 48. Kenjo s ID macrohomogeneous model for polarization and ohmic losses in a composite electrode, (a) Sketch of the composite microstructure, (b) Description of ionic conduction in the ionic subphase and reaction at the TPB s in terms of interpenetrating thin films following the approach of ref 302. (c) Predicted overpotential profile in the electrode near the electrode/electrolyte interface, (d) Predicted admittance as a function of the electrode thickness as used to fit the data in Figure 47. (Reprinted with permission from refs 300 and 301. Copyright 1991 and 1992 Electrochemical Society, Inc. and Elsevier, reepectively.)...

When no current flows through the polarizing circuit and there is equilibrium at the test electrode/electrolyte interface, the potential difference, Ee, between the test and reference electrodes is given by... 

However, high electrolyte conductivity on its own does not necessarily guarantee low polarization in a solid state cell. Electrode/electrolyte inter-facial resistance must also be taken into account, and in contrast to the more familiar situation with conventional aqueous systems where the solid electrodes are uniformly wetted by the liquid electrolyte, the all-solid configuration of the cell may create non-uniform contact at the interfaces. Differential expansion and contraction of electrodes and electrolyte may lead to poor contact (and consequent high internal resistance due to low effective electrode/electrolyte interfacial area) or even to a complete open circuit during cell operation. The situation is even more serious with secondary cells, as illustrated schematically in Fig. 9.4, where the effects... 

When j0 is very small, the region corresponding to linear polarization may not be accessible because residual currents due to the oxidation and reduction of impurities may be larger than the currents due to the electrode reaction under consideration. In addition, the ohmic resistance at the electrode—electrolyte interface can only be neglected if it is much less than the polarization resistance. 

Protonation of 189 or the dianion 193 occurs at the sites of highest negative charge density, which however may be modulated by the electric field strength at the electrode/electrolyte interface via the polarity of the solvent 511 ... 

The calomel electrode. Calomel and other mercurous halides disproportionate in a number of organic solvents, and attempts to use the calomel electrode in polar aptotic solvents, have, for the most part, been unsuccessful. For this reason, it is not advisable to replace the aqueous electrolyte of an ordinary calomel reference electrode with an electrolyte dissolved in an aptotic solvent. 

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