The electrochemical behaviour of iron oxides in dilute sulphuric acid and the interpretation of the flade potential of iron

The cathodic reduction of Fe₂O₃, FeOOH, and Fe₃O₄ in dilute sulphuric acid has been directly investigated using graphite paste electrodes containing the oxides. It has been found that these oxides sustain redox reactions at a high positive potential which is stabilised by the presence of ferrous sulphate in the solution and, at saturation, tends to coincidence with the Flade potential. The redox process can be formulated, for example, as Fe₂O₃(its)+2H⁺+2H₂SO₄+2e^?=2FeSO₄s+3H₂O(1) and the potential derived from the free energy change is approximately right. γ-oxides and hydroxyoxides of iron enter into reaction more readily than their α-analogues, and this would be expected on structural grounds.