Charge transfer at Fe/FeO(CaF2) electrodes at 1450 ‡C: Exchange current density, electrode capacitance, diffusivity

The kinetics of the electrode reaction Fe = Fe slag 2+ + 2e - has been investigated using the single and double pulse techniques. It was found that the exchange current densities are very large increasing from 2 to 10 A cm-2 in the range of Fe2+-concentration from 2 · 10-6 to 30 · 10-6 mole cm−3. The electrode capacitance increases from 50 ΜF cm-2 approximately linearly with the square root of Fe2+-concentration. An attempt was made to explain the concentration dependent part of the capacitance in terms of a model involving electrosorption of the speciesFe at the slag/iron interface. If the adsorbed iron ions are the intermediates in a consecutive charge transfer mechanism, the rate determining step is the transfer of iron between the adsorbed layer and the slag. On the other hand, it may be possible that the transfer is in one step with adsorption occurring in parallel.