SURFACE BLOCKING IN THE REDOX SYSTEM PT/[FE(CN)6]3-,[FE(CN)6]4- - AN AC IMPEDANCE STUDY

Electrochemical dc and ac measurements were made in the system Pt/x M [Fe(CN)6]3-, [Fe(CN)6]4- +0.5 M Na2SO4 in the range 2×10-6 ≤ x ≤ 2×10-2 at T = 298 K and pH 6 using the rotating disk technique. Depending on the defined prepolarization conditions, a partial blocking of the electrode surface was observed indicated by distinct changes of the impedance spectra. Transfer function analysis based on a model of a transport controlled reaction on a partially blocked surface gave quantitative information on the degree of surface coverage. Systematic variation of the experimental conditions allowed conclusions to be drawn about the chemical nature of the blocking species. © 1990.