Admittance-Plane Representation

The maximum value for the imaginary part of the admittance is equal to 1 /2Rg for the blocking system, and the characteristic angular frequency at the maximum is equal to (Vc = 1/ReC. 

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Figure 16.6 Admittance-plane representation for Re = 10 flcm, R = 100 flcm, and C = 20 fiF/cm. The blocking system of Table 16.1(a) is represented by A and dashed lines, and the reactive system of Table 16.1(b) is represented by O solid lines.

The complex-capacitance-plane plot is presented in Figure 16.11. The data are presented as a locus of points, where each data point corresponds to a different measurement frequency. As discussed for the impedance- and admittance-plane representations (Figures 16.1 and 16.6, respectively), the complex-capacitance-plane... 

A2.4 Representation in the complex plane A2.5 Resistance and capacitance in series A2.6 Resistance and capacitance in parallel A2.7 Impedances in series and in parallel A2.8 Admittance... 

The above analysis shows that in the simple case of one adsorbed intermediate (according to Langmuirian adsorption), various complex plane plots may be obtained, depending on the relative values of the system parameters. These plots are described by various equivalent circuits, which are only the electrical representations of the interfacial phenomena. In fact, there are no real capacitances, inductances, or resistances in the circuit (faradaic process). These parameters originate from the behavior of the kinetic equations and are functions of the rate constants, transfer coefficients, potential, diffusion coefficients, concentrations, etc. In addition, all these parameters are highly nonlinear, that is, they depend on the electrode potential. It seems that the electrical representation of the faradaic impedance, however useful it may sound, is not necessary in the description of the system. The systen may be described in a simpler way directly by the equations describing impedances or admittances (see also Section IV). In... 

Therefore admittance data can also be plotted in the complex plane (V versus F with (o implicit). Some researchers choose to display data in terms of the complex capacitance C( o>) here C( a>) = Y j(o)lj(o. The latter type of representation can be useful when examining the electrochemical response of electronically conducting polymer films. The low-frequency redox pseudocapacitance can be read directly from a plot of C" versus C at low frequency. 

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