On-line FFT faradaic admittance measurements. An application of broadband admittance spectral data to more unambiguous characterization of quasi-reversible systems

Frequency domain rate laws for the quasi-reversible faradaic process with nernstian d.c. behavior reduce to an algebraically simple high frequency limiting law for the faradaic admittance peak potential and magnitude. This result has been infrequently exploited because of experimental difficulties with obtaining accurate data at sufficiently high frequencies to obtain this limiting condition. However, on-line computerized FFT faradaic admittance measurement techniques now enable convenient, automated broadband data collection which encompasses the high frequency limit for all but the most facile electrode reactions. It is shown that results from the low and high frequency regions of the faradaic admittance spectrum yield consistent results with several known quasi-reversible systems. A procedure is recommended which makes use of the broadband data to permit two independent assays of the rate parameters, one from conventional phase angle cotangent analysis at low and moderate frequencies, and one from the high frequency limiting behavior. Consistent results from the two approaches imply greater certainty in mechanism and rate parameter evaluation than the routine methods which invoke a truncated examination of the response spectrum.