Unravelling the mechanisms controlling the electro-generation of ferrate using four iron salts in boron-doped diamond electrodes

Abstract

This article studies the mechanisms of electrochemical production of ferrate (VI) using a boron-doped diamond (BDD) electrode. Ferrate was synthesized using different current densities, electrolysis time and concentrations of Fe(NO3)3, FeSO4, FeCl3 and FeCl2. The ferrate generation rate was highly affected by the initial concentration and the type of iron salt. The results suggest that diffusion is the controlling mechanism at the BDD electrode. However, for iron salts with oxidation state +2, electron charge also takes place. Cyclic voltammetries showed that the oxidation peak that correlated with ferrate generation is close to the potential where •OH radicals occur. This indicates that a direct electron transfer from the BDD and an indirect oxidation through •OH radicals influenced the generation of ferrate. Although Fe(NO3)3 and FeSO4 oxidation does not perform as well as iron chloride salts in the generation of ferrate, they do not form chlorate and perchlorate. This study demonstrates that it is possible to produce a powerful oxidant that could be used for water treatment purposes without generating toxic by-products.