W. Weppner - Academia.edu (original) (raw)

Papers by W. Weppner

La conductivite ionique de CaF 2 est augmentee jusqu'a 200%, par addition de Al 2 O 3 , Bi 2 ... more La conductivite ionique de CaF 2 est augmentee jusqu'a 200%, par addition de Al 2 O 3 , Bi 2 O 3 ou CeO 2 . La conductivite peut atteindre 5•10 −5 Ω −1 cm −1 a 300°C, avec une enthalpie d'activation σT de 0,68 eV pour CaF 2 . Le courant est porte par des ions fluorure avec formation de CaO en relation avec des electrodes oxydes. L'emploi de l'electrolyte dans les cellules de concentration est possible

Annual Review of Materials Science, 1978

ABSTRACT Electrical methods offer advantages for the determination of kinetic and thermodynamic q... more ABSTRACT Electrical methods offer advantages for the determination of kinetic and thermodynamic quantities because of the transducer properties of fast ionic conductors. Further applications of such techniques depend upon an increased familiarity with them, and upon the availability of chemically compatible electrodes and suitable electrolytes for specific species in the temperature range of interest. Progress is being made in the search for new solid electrolytes for a variety of both cationic and anionic species. Various electrochemical techniques available for kinetic studies of solids have been compiled and tabulated. 153 references, 17 figures, 3 tables.

Materials for Advanced Batteries, 1980

High power density batteries require rapid equilibration of compositional inhomogeneities within ... more High power density batteries require rapid equilibration of compositional inhomogeneities within the mixed ionic-electronic conducting electrodes. Large enhancement of the ionic motion may be observed for semi-conducting materials with a small number of highly mobile electronic species. Metallic conduction is a disadvantage. In order to meet the various conflicting requirements, the coulometric titration curve should show large slopes at completely charged and discharged states.

Solid State Batteries, 1985

The coulometric titration technique provides phase equilibrium, thermodynamic and kinetic propert... more The coulometric titration technique provides phase equilibrium, thermodynamic and kinetic properties which are important for the behaviour of the system as a cathode material. Ternary systems offer the possibility to select the most favorable conditions for battery applications by variation of the composition of the constituents. The technique is illustrated for the ternary system Li-In-Sb at 400°C.

Fast Ion Transport in Solids, 1993

All applications, which make use of fast ion transport in solids, are galvanic cells and the impo... more All applications, which make use of fast ion transport in solids, are galvanic cells and the important regions, in which the voltage drops occur, are primarily the interfaces between the electrolyte and the electrodes. This places severe limitations on the applicability of the materials with regard to their chemical stability at every state of discharge of the galvanic cell. High thermodynamic stability and fast ion transport are contradictory requirements which may be overcome by complex disordered structures. Techniques have been developed to study fundamental thermodynamic and kinetic data of both pure ionically and mixed conducting materials in-situ with high precision and as a function of the composition.

Zeitschrift für anorganische und allgemeine Chemie, 1995

NaNb6Cl15 is prepared by heating Nb3Cl8, NaCl and Nb under Ar at 1 170 < T [K] < 1 270 form... more NaNb6Cl15 is prepared by heating Nb3Cl8, NaCl and Nb under Ar at 1 170 < T [K] < 1 270 forming black regular dodecahedra. It crystallizes in the cubic space group Ia3d (a = 2 041.7(2) pm at room temperature) and transforms to a tetragonal structure below 150 K (probably I41/acd, a = 2 037.2(6), c = 2 028.2(2) pm at 80 K). The Na+ ions are at room temperature dynamically disordered in a split position. Their mobility is investigated by IR spectroscopy and electrochemical methods.

Solid State Ionics, 1998

ABSTRACT The influence of electrochemical pretreatment on the long-term behaviour of electrodes o... more ABSTRACT The influence of electrochemical pretreatment on the long-term behaviour of electrodes of the type `oxygen, platinum/stabilized zirconia' was investigated. Working electrodes comprising a massive platinum contact on yttria-stabilized zirconia were equilibrated in an oxidizing gas phase and examined by means of impedance spectroscopy in the temperature range from 773 to 1173 K and in the oxygen partial pressure range from 1 to 101 325 Pa. After polarizing the working electrodes under applied voltages of −2.0 or +0.5 V against the reference electrode at 873 K in air and admitting relaxation periods of at least 250 h, the impedance analysis was repeated in the temperature interval between 773 and 873 K and in the same oxygen partial pressure interval as before. A significant increase of the electrode conductance was observed in both cases. The results indicate that the electrochemical performance of zirconia-based electrodes is not only determined by the catalytic properties of the metal, but in addition by the catalytic properties of the electrolyte.

Solid State Ionics, 1986

Abstract Solid state galvanic cells are investigated in view of their application for selective a... more Abstract Solid state galvanic cells are investigated in view of their application for selective and reversible determination of partial pressures of gaseous species which may not be transferred in the solid electrolyte. The activities of the mobile component in the electrolyte and the gas component under measurement are correlated by an auxiliary gas sensitive layer. Solid silver ion conductors which show high ionic conductivity at room temperature are preferably employed. The measurement of Cl 2 and NO 2 partial pressures is illustrated as examples of the solid state electrochemical technique. The devices may be miniaturized (“microionics”) and operated over a wide temperature regime.

Sensors and Actuators B: Chemical, 1992

Materials Science and Engineering: B, 2004

... 14] methods are employed to prepare rapidly a variety of functional materials, such ... elect... more ... 14] methods are employed to prepare rapidly a variety of functional materials, such ... electron microscope (SEM) (PHILIPS SEM XL 30) were employed for the materials characterization. ... The structure is related to common alkali metal molybdates and tungstates with the general ...

Materials Research Bulletin, 2002

ABSTRACT The electrical conductivity of SrSn1−xFexO3−δ increases with the Fe content and reaches ... more ABSTRACT The electrical conductivity of SrSn1−xFexO3−δ increases with the Fe content and reaches a value of ∼10−1 S/cm at 25°C at x=1. Compounds with low Fe content exhibit both ionic and electronic conductivity, while the higher Fe content perovskites are mainly electronic conductors with a conductivity independent of the oxygen partial pressure over a wide range from 0.21 to 10−22 atm.

Materials Research Bulletin, 1979

Journal of Solid State Chemistry, 1997

Journal of Power Sources, 2005

Journal of Physics D: Applied Physics, 2007

ABSTRACT A new class of low temperature proton-conducting-type hydrogen gas sensor was developed ... more ABSTRACT A new class of low temperature proton-conducting-type hydrogen gas sensor was developed using Dion–Jacobson type layered perovskite oxides. A laminated structure with a junction of charge carriers at the interface between a predominantly ionically and predominately electronically conducting material was prepared by using the multistep-impregnation-reduction method for the deposition of Pt on top of a perovskite oxide. The proton conductivity of the layered perovskite materials was studied between room temperature and 250 °C. The sensing characteristic was studied by using H2 concentrations between 1% and 7%. The optimum operating temperature of the sensor was found to be at 45 °C. The formation of the galvanic cell voltage is described in terms of reactions at the interfaces and the surface of the electrodes. The experimental results indicate the motion of electrons within the Pt and of protons within the perovskite oxide along the interface. Hence, modelling the system response upon a change in gas concentrations can be beneficial for understanding the individual processes and optimizing the overall performance.

Ionics, 2005

A novel electrochemical hydrogen sensor which consists of a solid electrolyte polymer (SEP) and c... more A novel electrochemical hydrogen sensor which consists of a solid electrolyte polymer (SEP) and catalytic active electrode operating at room temperature was fabricated and investigated. Nafion is utilized as polymer proton conducting membrane onto which a catalytic electrode was deposited by anin-situ impregnation reduction (I-R) technique. In this work, Pt was selected as active catalyst for hydrogen oxidation and the