Compensating the Effects of Frequency Dispersion in Mott–Schottky Analyses of Passive Films

The use of constant phase elements (CPE) to overcome the problem of frequency dispersion in Mott–Schottky (MS) tests has not been a common practice until recently. The present study is an effort to compensate the effects of frequency dispersion in individual single-frequency MS tests by using CPE. Instead of calculating the capacitance only from the imaginary impedances (which is standard in conventional MS tests), both components of the impedances are used to calculate the exponents and admittance constants of some CPEs, which are further converted to capacitances. This requires the real impedances to be corrected for the solution resistance. The developed approach is compared with those of previous studies and applied to the analyses of passive films formed on carbon steel in fresh and CO₂-loaded diethanolamine solutions.