Admittance and its use

Admittance is the inverse of impedance, and is represented by the symbol Y. In certain circumstances, admittance is very useful since 

These equations show the possibility of determination of Cd in the presence of the electroactive species. A good strategy is  

One assumes that the double layer admittance is that of a pure capacitor. Thus its value should be independent of frequency. The graphical variation of Y with Y is shown schematically in Fig. 11.9. More details may be found in Ref. 9. 

As a final point we call attention to the fact that a plot of Y vs. E has the same form as an a.c. voltammogram, i.e. it comprises a peak centred on the half-wave potential—this because the measured current is inversely proportional to Rct. 

If a fixed frequency sinusoidal perturbation is applied at a succession of fixed d.c. potentials, we can register the resulting alternating current and its phase angle vs. the d.c. potential. The form of the curves obtained gives information about the kinetics, and can also be used for analytical 

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