Double layer effects resistance

The total capacitance in the walls of the pores is given by C, = c,L. This capacitance is attributed to double-layer effects, so it is usually a function of the potential. It can also be used to describe the space-charge polarization at the semiconductor-liquid junction if the spatial distribution of electrical charge as a function of potential is known. An ideally polarizable interface with charge transfer can be described by considering the charge transfer as a resistance, ret, which goes in parallel to the capacitance so that the impedance element yields an impedance such as ... 

ABSTRACT. The effect of the electrolyte concentration and solvent on the electrochemical oxidation of Cr(CO)6 at microelectrodes has been investigated. It is shown that reproducible data are obtained in media without the deliberate addition of electrolyte or in very resistive solvents such as toluene. The voltammetric realises are interpreted in the light of ohmic drop, migration, kinetics and double layer effects. 

Some examples of the distortion of the polarization curves by the double-layer effect are shown in Fig. 3. Two generalizations can be made. First, the overall appearance of the polarization curves remains normal even when the double-layer effect causes a change of several orders of magnitude in the current density. More noticeable distortion, such as strong curvature or a maximum, appears only in extreme cases, and even then it may be mistaken for other effects, such as insufficient solution resistance compensation, diffusional limitations, or passivation. Therefore, significant errors can exist in the corrosion measurements without any obvious indication in the experimental polarization curves. Second, the double-layer effect changes the slope of the Tafel lines more drastically than the corrosion current density determined from the intersection of the Tafel lines. 

The error of the idealized polarization-resistance technique can be calculated from Eq. (26). The error, presented in Fig. 9, can be expressed as a function of two dimensionless parameters that include all variables [( o)c /2.3v i r][6 6 /(6 -hfe )] and d(j>2ldE. Parts of the curves are shown with a dotted line, indicating the conditions under which the polarization curve of the corroding metal is distorted by the double-layer effect to such a degree that this becomes obvious to the experimenter. As described in Section III.2, the overall appearance of the polarization curves often remains normal even when the double-layer effect causes a significant error in the corrosion measurements. However, under extreme conditions the effect becomes obvious. The dotted lines in Fig. 9 indicate the conditions for which the polarization curve is... 

Figure 9. Error in corrosion current density due to the neglect of double-layer effect for idealized polarization-resistance technique. ...

Figure 12. Error in corrosion current density due to the neglect of double-layer effect for a corrosion system with oxygen reduction (solid lines) or hydrogen evolution (dashed lines) as the cathodic process for idealized polarization-resistance technique. = 0.03 V, = 0.12 V, 1 1 electrolyte, Ch-2S ii cm (zo) /v = 0.0 (solid) or =1.0 (dashed). ...

Figure 8.13. (a) Cyclic voltammetric investigation of the Ir02/YSZ interface (inset shows the circuit used to model the data)19 and (b) Effect of catalyst-electrode mass on the polarization resistance Rp and the double layer capacitance Cd.19 Scan rate 20 mV/s, T=380°C, pO2=20 kPa. 

The tip current depends on the rate of the interfacial IT reaction, which can be extracted from the tip current vs. distance curves. One should notice that the interface between the top and the bottom layers is nonpolarizable, and the potential drop is determined by the ratio of concentrations of the common ion (i.e., M ) in two phases. Probing kinetics of IT at a nonpolarized ITIES under steady-state conditions should minimize resistive potential drop and double-layer charging effects, which greatly complicate vol-tammetric studies of IT kinetics. 

It is convenient to think of the diffuse part of the double layer as an ionic atmosphere surrounding the particle. Any movement of the particle affects the particle s ionic atmosphere, which can be thought of as being dragged along through bulk motion and diffusional motion of the ions. The resulting electrical contribution to the resistance to particle motion manifests itself as an additional viscous effect, known as the electroviscous effect. Further,... 

The net effect of the presence of the solution resistance on potential excitation methods is that the potential seen by the electrode solution interface is different from the potential applied by the potentiostat. This difference is current-dependent and the current is itself potential-dependent. The resistance also makes it more difficult to separate current components arising from the double-layer capacitance from the faradaic process. Similar complications arise for current excitations. 

In its most simple form, this means without effects such as adsorption or formation of coatings at the electrode surface36. The resistance, Rc, represents electrical conductivity of the electrolyte and is not a property of the electrode itself. The differential double-layer capacity, Cmetal surface of the metal-electrolyte interface, which is in equilibrium with an equal excess of charge but opposite in sign at the side of the electrolyte. 

The addition of the inert electrolyte affords other advantages. The most important point is that the conductivity of the solution increases (and thus the ohmic drop decreases through a decrease of the resistance of the cell, Rccw see Sect. 1.9). Moreover, the diffuse double layer narrows, being formed mainly by the ions of the inert electrolyte (with a sharp potential drop over a very short distance from the electrode surface). This makes the capacitance more reproducible and the Frumkin effects less obtrusive. Activity coefficients of the electroactive species are also less variable (and, therefore, quantities like formal potentials and rate constants), since... 

Effect of the Uncompensated Resistance and of the Double-Layer Charging... 

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