No abstract

We address two major and open questions on the ubiquitous and controversial constant-phase element (CPE) behavior in the electrochemical impedance spectroscopy (EIS) response of electric double layers (EDLs) and its relationship with surface properties. The first one concerns the physicochemical origin of this anomalous behavior, whereas the second one deals with the physical meaning of the CPE capacitance obtained from impedance data. For that purpose we have analyzed the EIS response of a well-controlled electrochemical reaction taking place on a surface electrode that was progressively modified by electrodissolution. A complete characterization of the surface structure was obtained by means of scanning with-light interferometry and X-ray diffraction and from a previous analysis based on atomic force microscopy. With regard to the first question, our results show direct evidence supporting the hypothesis that CPE behavior results from energetic rather than geometric heterogeneity (roughness). Regarding the second question, our results promisingly point to the CPE capacitance as a measure of the actual EDL capacitance for rough metal−electrolyte interfaces.

The kinetic roughening of dissolving polycrystalline pure iron has been studied. A depth analysis of surface images has shown two consecutive growth regimes characterized by different scaling anomalous properties: an initial intrinsic anomalous scaling evolving in the thick film limit towards the theoretically conjectured faceted anomalous scaling. This represents the first experimental evidence of such scaling as well as of such transition. The dynamics presented here may account for the striped surface pattern observed during the evolution of metals or alloys in a large number of processes.