Introduction
With the introduction of a constant phase element (CPE) as a replacement for the capacity in
EIS measurements, most of the experimentally obtained results could be fitted by
commercially available software (Gamry, Scribner, Solartron, etc.). Much better fit results
were obtained with CPE in comparison with the fit results obtained by using pure capacity,
represented by parallel plate condenser. Taking into account that the CPE defines
inhomogeneity of the surface in the electrochemical EIS experiments and inhomogeneity of
the charge distribution in solid state EIS measurements, it is reasonable to expect that better
fit for real systems is obtained by using CPE. The main problem in the use of commercially
available software with CPE is the fact that the capacity, obtained by fitting procedure, does
not have the dimension of capacity, i.e., F cm-2, or Ω-1cm-2 s, but its dimension is given
in Ω-1 cm-2 sa, where a is the exponent in the equation for the CPE [1] ( ZCPE = Zdl(jω)-a ).
This problem has been discussed in few papers [2-4] and recently Hsu and Mansfeld [5]
developed the equation for correction of capacity to its real value, in the case of parallel
connection of CPE and R, by using equation (1)...... |
