Elisabeth Siebert

Impedance spectroscopy analysis of La1 − xSritxMnO3-yttria-stabilized zirconia electrode kinetics

Abstract The impedance of the La 1 − x Sr x MnO 3 -Yttria-stabilized zirconia oxygen electrode has been analyzed as a function of the overpotential, temperature and oxygen partial pressure. At equilibrium, the impedance diagram is characterized by a large capacitive effect, approximately constant, and a resistance varying with the oxygen partial pressure as P O 2 − 1 2 The resistance activation energy is 1.8 eV in air. Under low anodic and cathodic overpotentials, the observed behavior is similar to that of metallic electrodes. This could be related to a limiting oxygen adsorption process in the triple contact zone. Under large anodic polarization, inductive effects set in at low frequencies with a significant decrease of the electrode resistance. Under large cathodic polarization, the onset of the electrocatalytic process due to the creation of oxygen vacancies in the electrode material is observed, as already reported. The impedance diagrams suggest a limiting diffusion process which is assumed to be the oxygen transport in the electrode material. A numerical calculation provides an estimate for the corresponding diffusion coefficient and the volume of the electrode material involved in the process.

Electrochemical recognition of metal cations by poly(crown ether ferrocene) films investigated by cyclic voltammetry and electrochemical impedance spectroscopy

Abstract The electrochemical behavior of the pyrrole-substituted crown ether ferrocene 1 was investigated in detail in 0.1 M TBAP+CH 3 CN by cyclic voltammetry (CV) and chronoamperometry. In the potential range 0–0.7 V, a reversible diffusion-controlled process was observed with a formal potential of 0.53 V corresponding to the ferrocene/ferricinium redox couple. Electro-oxidative polymerization of 1 was accomplished either by repeated CV scans, or by controlled potential electrolysis. The resulting polymer films were tested in acetonitrile electrolyte for the amperometric recognition of alkali and alkaline earth metal cations. Their remarkable recognition properties towards Ca 2+ and Ba 2+ cations have been confirmed by electrochemical impedance spectroscopy (EIS). EIS allowed construction of a calibration curve based on the variation of the low frequency capacity of the film as a function of the guest cation concentration, reflecting the variation of the formal potential between the free and the complexed immobilized redox couple. Capacity measurements using EIS appear to be an attractive method for cation sensing with films based on molecular redox receptors.

Electrochemical recognition of metal cations by redox-active receptors in homogeneous solution and in polymer films: some relevant examples

Abstract Examples of several molecular redox-active receptors containing a ferrocene redox centre and crown ether or bipyridyl moieties as binding site are presented. Their electrochemical recognition properties towards groups I and II (crown ether-based receptors) and Cu + (2,2′-bipyridine-based receptors) metal cations have been investigated by cyclic voltammetry in homogeneous solution. Among the four ferrocene-crown ether studied, Fcc 3 allowed the effective amperometric recognition of Ba 2+ and Ca 2+ cations owing to the growth of a new redox peak system at the expense of the original Fc/Fc + wave (two-wave behavior). In addition, comparison of the electrochemical features in the presence of Cu + cations of ferrocene monosubstituted (Fcb 1 ) and disubstituted (Fcb 2 ) by bipyridyl groups emphasized the beneficial “sandwich” effect on the recognition behavior of ferrocene-based receptors. Polymer films coated onto electrodes surfaces by electropolymerization of pyrrole-substituted Fcc 3 and Fcb 2 retained the complexation and the amperometric properties, studied by cyclic voltammetry, of the molecular receptors. Furthermore, capacity measurements using electrochemical impedance spectroscopy (EIS) appeared as a good method for detection and titration of metal cations with these polymer-modified electrodes.

Potentiometric selectivity and impedance characteristics of a NASICON-based ion selective electrode

Abstract The potentiometric response of the Na+ ion selective electrode based on NASICON (Na3Zr2Si2PO12) as well as the impedance of the NASICON/solution interface have been measured in NaCl, LiCl and KCl aqueous solutions. The behavior of the NASICON was successfully explained on the basis of the Eisenman model which involves an ion exchange process between the membrane and the solution. The apparent ion-exchange densities and potentiometric selectivity coefficients of the NASICON membrane have been determined for Na+, Li+ and K+ ions. The higher the apparent standard ion-exchange current density is, the better is the selectivity. However, no simple relationship can be established between these two parameters.

Noise analysis of NASICON ceramic dry electrodes

The noise and the impedance between two non-polarizable dry NASICON ceramic electrodes were investigated. The electrodes were placed on the ventral side of the forearm over inactive muscle area without contact paste. Significant noise was found in the bandwidth 1 Hz-100 Hz. This noise was more intense than the thermal noise of the resistive part of the electrode impedance, the amplifier voltage and current noise together. The power spectral density (PSD) of the observed noise follows an 1/f/sup /spl alpha// law with /spl alpha/=1,6 to 2. This excess noise probably has an electrochemical origin and can be related to the skin-electrode interface.

Electrocatalysis and morphology at cathode materials for the oxygen reaction on solid oxide ionic conductors

Abstract Electrocatalytic effects on solid oxide ionic conductors in high temperature systems are discussed. The oxygen electrode reaction on a solid electrolyte is depicted. Possible oxygen reduction pathways are reviewed as a function of the nature of the electrode and electrolyte surface. What is meant by electrocatalysis is defined and illustrated in two examples: the oxygen reduction on perovskites and on doped yttria-stabilized zirconia.

NASICON based electrodes for bioelectric signal measurements

A new easily reusable electrode which eliminates the need for a gel at the electrode-skin interface is proposed. It is based on a ceramic material whose Na+ ion conductivity is high at room temperature. The electrical properties of this ceramic based electrode are reported.

Ion exchange properties of NASICON-type ceramics—Application to ion selective electrodes

Abstract The ion-exchange properties of NASICON type ceramics of composition Na 3 Zr 2 Si 2 PO 12 were investigated in aqueous solutions of NaCl, LiCl and KCl. The solution analysis shows that the [Zr 2 Si 2 PO 12 ] framework strongly prefers Na + ion relative to K + and Li + . The exchange current density of the alkali-cations at the NASICON/solution interface determined by impedance measurements varies in the order Na + >Li + >K + . These results agree well with the selectivity coefficients of Na + ion selective electrodes based on NASICON. The interference process to alkali-cations in the NASICON based electrode was shown to result from an ionic exchange. The selectivity was suggested to be governed by the mobility of the cation inside the NASICON framework.

Chemically modified PTFE-carbon as a solid state oxygen sensor electrode material

Abstract Transition metal complexes such as [Fe, (pyridin2) n ] 2+ have been synthesized and grafted on PTFE carbon. In aqueous electrolyte, these materials display catalytic properties for the oxygen evolution/reduction electrode reaction. The behaviour of a chemically modified PTFE carbon electrode in a PbSnF 4 electrolyte oxygen sensor in the 10 −3 atm o 2 −1 atm range at 100°C and 160°C is reported.