Perovskite-type nanomaterials of the compositions La1-yCayMn1-xB '' O-x(3 +/-delta) with B '' = Ni, Fe; x = 0.2, 0.5 and y = 0.4, 0.25 were prepared using two different preparation routes (synthesis by precipitation and the PVA/sucrose method) at 500 degrees C-700 degrees C. The calcined products of the syntheses were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX) and physisorption measurements. The materials from the PVA/sucrose method contain particles with diameters from 33 nm to 48 nm, generate specific surface areas up to 33m(2)/g and form pure compared to 45 nm-93 nm and up to 18m(2)/g from precipitation method which contain a significant amount of sodium ions. The agglomeration process was analyzed for one nanomaterial (B '' = Fe, x = 0.2, y = 0.4) from the PVA/sucrose method using temperature dependent XRD showing only a slight growth (4.3%) of nanoparticles at 600 degrees C. The materials from the PVA/sucrose method turned out to be more suitable as electrode materials in electrochemical applications (SOFC, sensors) because of smaller particle sizes, higher specific surface areas and purity. (c) 2018 Elsevier Masson SAS. All rights reserved.

Oxygen solid electrolyte coulometry (OSEC) based on electrochemical cells made of yttria-stabilized zirconia (YSZ) is a long-standing method for gas sensing, material characterization as well as biological or medical measurements of oxygen exchange.Newer approaches are directed on analytical applications for chromatography or dissolved gas measurements.With optimized cell construction and operating conditions, the method enables the detection of gaseous quantities down to the picomolar range.The contribution gives an overview on the most important parameters, the characteristics and requirements regarding the sensors and also on actual developments.

A new setup for characterization of solid material oxygen exchange and conductivity in a broad oxygen partial pressure range and at elevated temperatures is presented. The development target of this setup is directed towards the detection of ultra-low amounts of exchanged oxygen. For this, electrochemical cells made of yttria-stabilized zirconia (YSZ) were optimized and applied in a flow-through arrangement. The design and process measures enable a lower limit of detection below 100 pmol of exchanged oxygen. Furthermore, the system characteristics concerning oxygen dispersion, titration efficiency and electrode kinetics are described.

Grain boundaries of single-phase solid electrolyte ceramics are often less conductive in comparison with grain volumes [1,2]. Another situation can appear in composite materials consisting of solid electrolytes (SE) and dielectric phases (Ins). The SE/Ins grain boundaries can exhibit higher conductivities compared to the bulk of the solid electrolyte grains in composites where the epitaxial connecting zone between SE and Ins is characterized with certain structures containing irregularities and additional defects [3]. It was found for example, that epitaxial films of yttria stabilized zirconia (YSZ), formed on MgO single crystals, have oxide ion conductivities, which are 3–4 orders of magnitude higher than those of YSZ in the temperature range 600–800 °C [4]. Herewith, the formation of intermediate layers between YSZ and MgO phases with the thickness 1.6 nm was observed. Elevated oxygen ion conductivities of such composites can be realized with ceramic structures in connection with appropriate conductivity parameters of the composite components. For example, this phenomenon was observed in systems like LiJ/Al2O3, Ce1-xSmxO2-x/2/Na2CO3, Na2CO3/Na2SO4, Ba(NO3)2–Al2O3 and Ce0.8Gd0.2O1.9/MgO [5]. Conductivity model of the nano-composite ceramics consisting of solid electrolyte (SE) and the dielectric phases (Ins) proposed in the assumption that the conductivity of the grain boundaries (SE/Ins) is higher than the bulk conductivity of the SE particle and the conductivity of SE/SE grain boundaries. The particle size of composite ceramics (SE+Ins) at which the conductivity may exceed the conductivity of the single phase solid electrolyte ceramics is estimated depending of grain boundary thickness and the bulk and grain boundary conductivities of the composite ceramic components. To test the model, the composite ceramics based on magnesium oxide (MgO) and cerium dioxide doped with samarium oxide (SDC) were prepared. The total electrical conductivity of the SDC/MgO composite ceramics with 50 % mol. of dielectric magnesium oxide measured in air at temperature 250-550 °C was comparable with the conductivity of the pure SDC single phase ceramics. Such situation can be explained by appearance of new more conductive areas in composite ceramics. We propose that these high conductive areas can be SDC/MgO grain boundaries, which are only the new conductivity areas in composite ceramics in comparison with the single phase SDC ceramics. Optimization of grain size and uniformity of distribution of components in the composite ceramics can open up the possibility to produce more conductive oxide solid electrolyte materials, but verification of this assumption requires additional investigations with composition and structure of new nano-composites in this system.

Coulometric solid electrolyte sensors and measuring systems are gaining in importance for a variety of applications. One of their main advantages is their relatively precise function based on Faraday's law enabling calibration free performance over long time spans. By using devices with yttria-stabilized zirconia (YSZ) as solid electrolyte for the measurement of very small amounts of analytes like oxygen or gases reacting with oxygen ions, deviations of the measured cell current from the Faraday's law become visible. In this work, these deviations were measured at tubular YSZ cells with 6mm outer diameter, 1mm electrolyte thickness and 60mm length with the Hebb–Wagner method, using ultra clean nitrogen at different temperatures and oxygen partial pressures. At constant potentials of the measuring electrode between −850 and −350mV vs. Pt/air reference the deviation of the cell current from the Faraday's law was found to be caused completely by the hole conductivity of YSZ within the possible precision of measurement. At constant potentials below −1400mV the deviation is significantly lower than predicted by the values for electron conductivity already published for YSZ by Park and Blumenthal in 1989. Beside these static deviations at constant electrode potentials the coulometric cells show a dynamic non-Faraday charge transfer after potential steps of −50mV. This charge transfer, depending on temperature, start potential and prehistory, ranges between 0.45 and 310mAs. It is caused, inter alia, by oxygen release from the electrolyte and the porous environment of the electrode. Since the values of this charge transfer outnumber the targeted precision of coulometric measurements of traces gases by several orders of magnitude these measurements have to be carried out at constant electrode potentials.

Since zirconia-based solid electrolyte sensors are economic, space-saving and long-term stable devices, they could be an useful alternative for mass spectrometry systems for the determination of traces of volatile substances in gas mixtures. Here we give an overview on sensor related parameters of zirconia-based solid electrolyte sensors, such as selectivity and detection limit. Furthermore, we show two possibilities for increasing the selectivity of these sensors and also that it is possible to decrease the lower limit of detection into the vol.-ppb range that corresponds to a lowering of about 4 orders of magnitude compared to commercially available state-of-the-art solid electrolyte sensors.

Composite ceramics based on magnesium oxide (MgO) as insulator (Ins) with gadolinium doped ceria (GDC) as solid electrolyte (SE) were prepared for model verification. It was found that SE/Ins grain boundaries exhibit conductivities 4–8 times higher than those of SE single phase material despite the fact that in this work the grain sizes of these composite ceramics were not small enough for the formation of a continuous network of the SE/Ins grain boundaries. This result indicates that the proposed model and strategy to manufacture composite materials with significantly higher ion conductivities can be used successfully, if an appropriate technology for establishing nanodispersions of homogeneously distributed components is available.

Coulometrische Festelektrolytsensoren werden in zunehmendem Maß für verschiedene Applikationen, z.B. für die Sauerstoffmessung und die Forschung an keramischen Materialien eingesetzt.Einer ihrer wesentlichen Vorteile betrifft ihre relativ genaue Signalabhängigkeit vom Faradayschen Gesetz, die einen kalibrierfreien Betrieb über einen langen Zeitraum ermöglicht.Der Einsatz dieser Sensoren zur Messung von Spurenkonzentrationen im ppm-und ppb-Bereich offenbart Abweichungen vom Faradayschen Gesetz, die durch die elektronische Leitfähigkeit des Elektrolyts (statisch) sowie durch Potential-und Temperaturänderungen oder elektromagnetische Einstreuungen (dynamisch) verursacht werden.Die Ergebnisse belegen, dass die bei Potentialen zwischen -900 und -350 mV gegen eine Pt/Luft-Referenzelektrode gefundenen statischen Abweichungen vollständig durch die Defektelektronenleitfähigkeit verursacht werden.Die bei Potentialen unter -1400 mV gemessenen Abweichungen beruhen im Wesentlichen auf der Elektronenleitfähigkeit des Festelektrolyts und sind deutlich niedriger als vergleichbare Literaturangaben.Der an einer Rohrzelle mit 6 mm Außendurchmesser, 1 mm Elektrolytdicke und 60 mm Länge gemessene Ladungstransfer nach einem Potentialsprung um -50 mV beträgt 0,45 -310 mAs.Diese z.T. relativ hohen Werte, die oft den während einer coulometrischen Bestimmung aufzulösenden Messwert deutlich übersteigen, unterstreichen die Wichtigkeit der präzisen Potentialkontrolle bei coulometrischen Messungen.Durch die Berücksichtigung dieser Abweichungen konnte demonstriert werden,

Oxygen surface exchange and oxygen chemical diffusion coefficients of LaNi 0.4 Fe 0.6 O 3− δ ceramics are determined via conductivity relaxation method after stepwise change of temperature in the range of 700–950 °C in air and Ar/O 2 gas flow at oxygen partial pressures ( p_O_2 ) of 4 Pa, 18 Pa, 37 Pa, 47 Pa and 59 Pa. The highest conductivity (about 160 S·cm −1 ) is found at 950 °C in air. No oxygen exchange ( δ = 0) below 700 °C is observed in the investigated p_O_2 range. The oxygen exchange coefficients determined in reduction mode are higher than those determined in oxidation mode. This is explained by clusterization of oxygen vacancies on the surface of the sample investigated in oxidation mode. The opposite tendency is found for chemical diffusion coefficients. Unlike surface, the oxygen vacancies of the volume region are probably not clustered and have predetermined the higher oxygen diffusion mobility of the sample treated in oxidation mode.

Crystal structure,thermal expansion, oxygen non-stoichiometry, electrical conductivity and diffusion characteristics of two analogous LaFe0.7Ni0.3O3‑d and PrFe0.7Ni0.3O3‑d compositions were investigated depending on temperature (201000 °C) and oxygen partial pressure (0.6–21000 Pa). The found oxygen diffusion and oxygen exchange coefficients for the both compositions at similar conditions are near to each other and varied in the range of 110‑7110‑5 cm2s‑1 and 510‑6110‑4 cms‑1, respectively.

Nitrogen oxides play an important role in combustion processes, as a metabolite in the human body, and in air in troposphere as well as in stratosphere. Solid electrolytes are well-suited for high-temperature electrochemical devices and have shown high potential for many applications in industry and automotive applications. Such NOx sensors mostly based on alkaline nitrate electrolyte are used in potentiometric mode, so far. In this paper, the newly developed NOx sensor is described which is based on barium nitrate composites as an electrolyte which works in an amperometric mode. That sensor made of thick film technique was investigated respecting the chemical and thermodynamic stability of the barium nitrate solid electrolyte, the optimal operation temperature, sensitivity and long-term stability. Due to the required high accuracy in temperature determination and regulation, three different temperature measurement techniques in the range of 100–1000°C have also been investigated. The sensor works in the NOx concentration range of 1–90ppm between 320 and 480°C. The cross sensitivity towards oxygen was observed, whereas CO2 in small concentrations does not influence the sensor signal at 360°C.

The development and utilization of solid electrolyte-based coulometric techniques for the investigation of different oxygen exchange processes of solids or liquids, oxygen or hydrogen permeability through membranes, and generation of gas flows with well-defined oxygen concentration is briefly reviewed. The method based on Faraday’s law may be used alternatively or additionally to thermogravimetry, gas chromatography, chemical analysis, spectroscopy, and X-ray or neutron diffractometry in a wide oxygen partial pressure region (10−20 to 105 Pa) unaffected by temperature. The detection limit of exchanged oxygen is determined by a current- and voltage-measuring technique and is now not lower than 50 ng for devices operating in carrier gas mode.

Coulometric solid electrolyte sensors based on stabilized zirconia were characterized with respect to the electronic conductivity of the solid electrolyte and their electrochemical activity of oxygen, hydrogen and hydrocarbon conversion.The temperature dependency of the electronic conductivity as well as the elevated noise of the coulometric cell at the working temperature restrict the limit of detection of coulometric titration.The article contains investigations of parameters influencing that detection limit and approaches to decrease it to the ppb-range.

Crystal structure, thermal expansion, oxygen non-stoichiometry, electrical conductivity and diffusion characteristics of two analogous LaFe0.7Ni0.3O3−δ and PrFe0.7Ni0.3O3−δ compositions were investigated depending on temperature (20–1000 °C) and oxygen partial pressure (0.6–21000 Pa). The found oxygen diffusion and oxygen exchange coefficients for the both compositions at similar conditions are near to each other and varied in the range of 1·10−7–1·10−5 cm2·s−1 and 5·10−6–1·10−4 cm·s−1, respectively.

Coulometric solid electrolyte sensors based on stabilized zirconia were characterized with respect to the electronic conductivity of the solid electrolyte and their electrochemical activity of oxygen, hydrogen and hydrocarbon conversion. The temperature dependency of the electronic conductivity as well as the elevated noise of the coulometric cell at the working temperature restrict the limit of detection of coulometric titration. The article contains investigations of parameters influencing that detection limit and approaches to decrease it to the ppb-range. 1 Einleitung

Electrochemical solid electrolyte sensors based on Yttria Stabilised Zirconia (YSZ) with mixed potential electrodes are suited for in-situ measurements of low concentrations of combustibles like hydrogen, carbon monoxide or hydrocarbons and also nitrogen oxides. The parameters sensitivity, selectivity and long-term stability of these sensors are correlated mainly with the performance of the electrode material. This work is directed on the investigation of newly developed conductive polymer composite materials (CPC) based on polyaniline (PANI). These materials have been characterised with respect to their morphology, thermal stability, catalytic activity and electrochemical behaviour on solid electrolytes in gases containing hydrogen, ethene and propene. For the first time it could be demonstrated, that CPC, consisting of PANI and different metal oxides or metal salts can be used at high temperature measurement up to temperatures of 450°C because of improved thermal properties.

The potential use of a double B mixed-perovskite as a promising cathode material in intermediate temperature solid oxide fuel cells (IT-SOFCs) has been anticipated as a result of this work. A thorough investigation of some important parameters like thermal stability, thermal expansion, oxygen non-stoichiometry, electrical conductivity and diffusion characteristics of the PrNi0.6Fe0.4O3-delta ceramic sample have been investigated as functions of temperature (20-1000 degrees C) and oxygen partial pressure (0.6-21,000 Pa). According to the measurements, the composition was phase stable at pO(2) > 1 Pa up to 1000 degrees C and shows p-type semiconductivity with a low conductivity versus pO(2) dependence.The perovskite has been found to have comparable thermal expansion coefficients with those of commonly used solid electrolytes like CeO2 and ZrO2 based oxides. In case of the chemical diffusion experiments higher oxygen diffusion mobility observed during reduction processes in comparison with those during oxidation have been explained by the already known formation of neutral defect clusters. (c) 2011 Elsevier B.V. All rights reserved.