Isabelle Frateur

Constant-Phase-Element Behavior Caused by Resistivity Distributions in Films I. Theory

I. Theory Bryan Hirschorn,* Mark E. Orazem,** Bernard Tribollet,** Vincent Vivier,*** Isabelle Frateur, and Marco Musiani*** Department of Chemical Engineering, University of Florida, Gainesville, Florida 32611, USA Laboratoire Interfaces et Systemes Electrochimiques, UPR 15 du CNRS, Université Pierre et Marie Curie, 75252 Paris cedex 05, France Laboratoire de Physico-Chimie des Surfaces, UMR CNRS-ENSCP 7045, Ecole Nationale Supérieure de Chimie de Paris, Chimie ParisTech, 75005 Paris, France Istituto per l’Energetica e le Interfasi, Consiglio Nazionale delle Ricerche, 35127 Padova, Italy

Constant-Phase-Element Behavior Caused by Resistivity Distributions in Films II. Applications

II. Applications Bryan Hirschorn,* Mark E. Orazem,** Bernard Tribollet,** Vincent Vivier,*** Isabelle Frateur, and Marco Musiani*** Department of Chemical Engineering, University of Florida, Gainesville, Florida 32611, USA Laboratoire Interfaces et Systemes Electrochimiques, UPR 15 du CNRS, Université Pierre et Marie Curie, 75252 Paris cedex 05, France Laboratoire de Physico-Chimie des Surfaces, UMR CNRS-ENSCP 7045, Ecole Nationale Supérieure de Chimie de Paris, Chimie ParisTech, 75005 Paris, France Istituto per l’Energetica e le Interfasi, Consiglio Nazionale delle Ricerche, 35127 Padova, Italy

The Global and Local Impedance Response of a Blocking Disk Electrode with Local Constant-Phase-Element Behavior

Numerical methods were used to calculate the influence of geometry-induced current and potential distributions on the impedance response of a blocking disk electrode with a local constant-phase element behavior. While the calculated global impedance is purely capacitive, the local impedance has high-frequency inductive loops that were observed in experiments conducted on a stainless steel electrode in 0.05 M NaCI + 0.005 M Na 2 SO 4 electrolyte. The calculated global impedance responses are in good agreement with experimental results obtained using both the steel electrode and a glassy-carbon disk in KCl electrolytes of differing concentrations. The computed local and both local and global ohmic impedances are shown to provide insight into the frequency dispersion associated with the geometry of disk electrodes.

Interfacial pH measurement during the reduction of dissolved oxygen in a submerged impinging jet cell

A pH sensor-grid assembly is used in a submerged impinging jet cell to measure the interfacial pH during the reduction of dissolved oxygen in well controlled flow conditions. Experiments were performed in a 0.5m K2SO4 solution with and without carbonate ions. In each case a good agreement between experiment and theory is found. In particular it was confirmed that, in the absence of chemical reaction and for a totally mass transport controlled oxygen reduction reaction, stirring has no influence on the interfacial pH.

Application of the impedance model of de Levie for the characterization of porous electrodes

From the de Levies theory for a porous electrode, the impedance can be expressed in function of the cylindrical pore characteristics: the pore length, the pore radius and the number of pores. If the pores have a finite length, these parameters can be regressed from the experimental impedance diagrams. In the case of a semi-infinite pore length, only the product r3/2n can be obtained. In this paper, two practical examples of porous electrodes were presented: the corrosion of cast iron in drinking water and the electrodissolution of copper in 1 M hydrochloric acid solution. In each case, the pore parameters were assessed.

Corrosion mechanisms of steel concrete moulds in contact with a demoulding agent studied by EIS and XPS

The behaviour of E24 mild steel was studied by XPS analysis and electrochemical impedance spectroscopy (EIS) in a filtered solution of cement (pH 13), and an alkyl N-aminodiphosphonate aqueous solution called Aquadem® (7⩽pH⩽13). XPS results showed that the corrosion products developed in both media consisted of Fe2O3, covered by a very thin layer of goethite. The thickness of this oxide layer was estimated to be 3 nm. XPS analysis also demonstrated the adsorption of Aquadem® on the outer layer of FeOOH for pH lower than the zero charge pH of goethite (7.55). From XPS and EIS results, physical models of the E24 steel/electrolyte interface are proposed as a function of pH. For 11⩽pH⩽13, the steel is covered by a passive film, while for pH⩽10, pitting corrosion takes place. At pH 7, an additional mass transport phenomenon must be taken into account. The fitting procedure provided values for several physical parameters (electrolyte resistance, passive film resistance), from which the film capacitance and the dielectric constant of the oxide layer were calculated.

Electrodeposition of PbO2 + CoOx composites by simultaneous oxidation of pb2+ and Co2+ and their use as anodes for O2 evolution

Abstract PbO2+CoOx composites have been deposited by anodisation of sulphamate solutions containing Pb2+ and Co2+ ions. The effect of experimental variables, like total Co2++Pb2+ concentration, Co2+/(Co2++Pb2+) ratio, potential, pH and angular speed of the anode, on the deposit composition has been investigated. The results are discussed according to the theories developed for the cathodic deposition of alloys, concluding that the system conforms to the trends typical of irregular deposition. XRD and XPS analyses have shown that the deposits are amorphous, but have not allowed to fully elucidate the nature of the Co containing compound(s) codeposited with PbO2. When used as anodes for oxygen evolution in aqueous NaOH, the PbO2+CoOx composites exhibit Tafel slopes of ca. 60 mV decade−1 and a reaction order of 1 with respect to OH−. Their overpotential is similar to that of PbO2+Co3O4 composites prepared by anodisation of suspensions. A marked activation of the PbO2+CoOx electrodes, during ca. 3 days of continuous oxygen evolution, is explained as the result of an increase of the Co surface concentration, as shown by XPS and impedance data.

Modeling of the cast iron/drinking water system by electrochemical impedance spectroscopy

Among the various causes of free chlorine consumption in drinking water distribution networks, the internal corrosion of pipes has not been so far seriously considered. This work focused on the corrosion study of cast iron, as a representative material of those networks, in non-chlorinated and chlorinated waters, by both electrochemical impedance spectroscopy and classical photographic observations. The results collected with cast iron rotating disk electrodes show that the behavior of cast iron depends only on the presence or absence of free chlorine and not on its concentration. Moreover, they lead to a scheme of different corrosion products layers based on the porous electrode theory of de Levie. This physical model describes the behavior of cast iron with and without free chlorine and at any time of immersion. The experimental impedance diagrams were at first fitted by the measurement model developed by Orazem et al. in order to identify the stochastic error and to delete non-stationary points. Then the regression of the physical model to the data provided the value of the anodic charge transfer resistance and, in this way, the value of the corrosion current. As the anodic charge transfer resistance was found to have the same order of magnitude as the polarization resistance, a simpler technique than the electrochemical impedance can be used to assess the corrosion rate.

Experimental Issues Associated with Measurement of Local Electrochemical Impedance

A detailed analysis from both numerical calculations and experimental results is presented for the local electrochemical impedance spectroscopy (LEIS) measurements of a disk electrode, which accounted for the placement of the LEIS probe above the electrode surface. The calculations for an electrode with a local constant phase element behavior were in excellent agreement with experimental observations for a stainless steel electrode in a Na 2 SO 4 /NaCl (pH 4) electrolyte. Measurement of the local impedance at two positions above the electrode surface allowed estimations of the local interfacial impedance and the local ohmic impedance, which were in excellent agreement with the simulations. The results demonstrate that the local impedance measurement itself cannot be used to estimate the surface area sampled by the LEIS probe. The area sampled must be determined instead by the probe geometry.

Free chlorine consumption induced by cast iron corrosion in drinking water distribution systems

Among the various causes of chlorine consumption in drinking water distribution networks, corrosion has not been so far seriously considered. This work focused on the corrosion study of cast iron, as a representative material of those networks, by both electrochemical methods (steady-state curves, corrosion potential and electrochemical impedance data) and classical photograph observations in the absence and in the presence of chlorine. From impedance results and photographs, a scheme of the different corrosion products layers, that is based on the de Levies theory, is proposed. By fitting this physical model to experimental impedance diagrams, the anodic charge transfer resistance can be extracted and thus a reliable value of the corrosion rate can be given. The general conclusion is that free chlorine is not electrochemically consumed at the metal surface though it is more easily reducible than oxygen. Therefore, the corrosion of cast iron pipes induces only a chemical decay of chlorine corresponding to its reaction with ferrous ions released by iron dissolution and the total consumption rate is exactly obtained from the corrosion current density.