Electrooxidation/electroreduction processes at composite iron hydroxide layers in carbonate-bicarbonate buffers

The electrooxidation/electroreduction processes at precipitated iron hydroxide layers on platinum electrodes have been studied in carbonate-bicarbonate buffers at 25°C by using electrochemical methods. The initial characteristics and properties of the hydrous iron hydroxide were changed by varying the precipitation conditions of the chemically formed active materials. Different potentialtime perturbation programs were employed to analyse the contribution of redox couples within the composite iron hydroxide layers on platinum electrodes and the corresponding electrochemical responses were compared with results obtained for massive iron electrodes in the same solutions. The complex electroreduction and electrooxidation processes are discussed on the basis of a reaction model which takes into account the incorporation of FeCO₃ in the hydrous iron hydroxide layer and its oxidation to FeOOH species, which in turn can participate in electroreduction reactions yielding Fe₃O₄, Fe(OH)₂, and soluble Fe(II) species.