The mechanism of the oxygen reduction on rust-covered metal substrates

Oxygen reduction is a major cathodic partial reaction during the corrosion of iron. The reaction is greater than the H+ reduction reaction for pH values >4. In the same pH range the iron surface is covered by insoluble oxide layers like rust scales. As rust scales are reduced in the potential range of the oxygen reduction, it was the aim of this study to analyse the relation between the kinetics of the oxygen reduction and the reduction of the rust layer. The results presented in this paper show that oxygen is predominantly reduced within the rust scale and not at the metal/electrolyte phase boundary. In order to allow any oxygen reduction, the rust layers have to be reduced. Oxidized rust scales, which are nearly free of Fe2+ states, inhibit the reduction of oxygen completely.

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