Interpretation of the Impedance Comprising Negative Capacitance and Constant Phase Elements on Iron Electrode in Weakly Acidic Media

The negative low-frequency capacitance that appears in interpretations of impedance of the iron electrode in weakly acidic solutions is shown to arise in the case of interaction of two consecutive nonequilibrium flows that constitute a two-stage anodic faradaic process of intermediate adsorption in the prepassivation potential range. The low-frequency capacitance is negative throughout a potential range where the logarithm of rate constant vs. potential (logk vs. E) dependence has the higher slope for the limiting stage. The low-frequency capacitance becomes positive at higher anodic potentials and for the other limiting stage.