Inhibition of the redox system Fe 2+/Fe 3+ by organic onium cations on a rotating gold disc electrode

Abstract

The inhibition effects of organic quarternary phosphonium and arsonium cations as well as dibenzylsulfoxide on the systems Au/0·2 M H 2SO 4 + 0·01 M Fe 2+ or Fe 3+ respectively has been investigated using rotating disc electrode technique and potentiostatic measurements under steady-state conditions. The results show relatively high inhibition effects in the charge transfer controlled potential ranges for reduction of Fe 3+ as well as oxidation of Fe 2+, whereby the Tafel slopes increase to b ± = ± 220 ± 20 mV at T = 298°K. The electrochemical reaction order with respect to the inhibitor concentration is z ± = −0·8 ± 0·05. The inhibition effect in the cathodic limiting diffusion range is relatively low compared to that in the charge transfer controlled ranges. However, the inhibition effect in the anodic limiting diffusion range is in the same order of magnitude as in the charge transfer controlled ranges. The observed inhibition effects are interpreted in terms of different inhibition mechanism. The most probable interpretation can be given by assuming a reactive coverage of the interface inhibitors to a relatively high degree.