Electrochemical behavior of iron in acetonitrile investigated by electrochemical impedance spectroscopy

The anodic dissolution mechanisms of iron in acetonitrile solution containing water have been studied by electrochemical impedance spectroscopy (EIS). Firstly, the influence of water was investigated by measuring the i-E curve. There were four anodic regions in the i-E curve, i.e., (i) the inert region, (ii) the first active dissolution region, (iii) the current plateau region and (iv) the second active dissolution region. The potential of first active dissolution region (ii) shifted to negative with the increase of the water concentration. The electrochemical impedance was measured at each anodic region. An inductive loop was described on the Nyquist plot of electrochemical impedance in the anodic regions (ii) and (iv), indicating the presence of reaction intermediate. A negative resistance was observed in the anodic region (iii), meaning the formation of oxide films on the iron electrode. The dissolution mechanisms of iron were proposed on the basis of the above-mentioned results and the spectrophotometric analyses of Fe(II) and Fe(III) dissolved during electrolysis. The numerical simulations were performed to confirm the proposed mechanisms and to obtain the kinetic parameters.