Über den Effekt von Stickstoffsubstitution auf die strukturellen Eigenschaften von polykristallinem Galliumoxid und die elektrische Leitfähigkeit von amorphen Lanthangallat Dünnschichten

The ammonolysis of b-gallium oxide (b-Ga2O3) was analyzed systematically in order to obtain information about structural aspects and thermodynamics of the system Ga2O3-GaN. This study focuses on the possible formation of gallium oxynitride (GaON) intermediates and the soluibility of nitrogen in the oxide sublattice and its resulting effects on the crystal structure. This was realized by employing ex situ X-Ray and neutron diffraction techniques (XRD, ND). In an additional set of experiments we prepared nitrogen containing lanthanum gallate (LaGaO3) layers by means of Pulsed Laser Deposition (PLD) in presence of nitrogen species. Those layers were deposited on single crystalline aluminum oxide (Al2O3) and yttria stabilized zirconia (YSZ) substrates. Electrochemical impedance spectroscopy (EIS) and a modified Hebb-Wagner DC-setup were used to determine the electrical conductivities of the lanthanum gallium oxynitride (LaGaOxNy)-layers. The observation of electrochemical properties of the system leads to information about the underlying defect chemistry. The presence of nitrogen in the material is confirmed by means of electron probe micro analysis (EPMA). Structural and morphological aspects are monitored with ex situ XRD-methods

Über den Effekt von Stickstoffsubstitution auf die strukturellen Eigenschaften von polykristallinem Galliumoxid und die elektrische Leitfähigkeit von amorphen Lanthangallat Dünnschichten

The ammonolysis of b-gallium oxide (b-Ga2O3) was analyzed systematically in order to obtain information about structural aspects and thermodynamics of the system Ga2O3-GaN. This study focuses on the possible formation of gallium oxynitride (GaON) intermediates and the soluibility of nitrogen in the oxide sublattice and its resulting effects on the crystal structure. This was realized by employing ex situ X-Ray and neutron diffraction techniques (XRD, ND). In an additional set of experiments we prepared nitrogen containing lanthanum gallate (LaGaO3) layers by means of Pulsed Laser Deposition (PLD) in presence of nitrogen species. Those layers were deposited on single crystalline aluminum oxide (Al2O3) and yttria stabilized zirconia (YSZ) substrates. Electrochemical impedance spectroscopy (EIS) and a modified Hebb-Wagner DC-setup were used to determine the electrical conductivities of the lanthanum gallium oxynitride (LaGaOxNy)-layers. The observation of electrochemical properties of the system leads to information about the underlying defect chemistry. The presence of nitrogen in the material is confirmed by means of electron probe micro analysis (EPMA). Structural and morphological aspects are monitored with ex situ XRD-methods

Redox-stable high-performance thin-film solid oxide fuel cell

In this work, a mechanically redox-stable SOFC with a 1 µm thin-film sol-gel electrolyte is presented. With this electrolyte a power output larger than 1.25 W/cm2 at 0.7 V and an operating temperature of 600 °C could be demonstrated. Half cells were re-oxidized in excess air, in order to test the redox stability of these SOFCs. No cracks were found in the sol-gel electrolyte after re-oxidation for 4 hours at 600 °C and 30 minutes at 800 °C, respectively. Due to the fact, that the energy release rate is proportional to the thickness of the thin-film, a thinner film is more stable against cracking than a thicker film at constant tensile stresses. The SOFC with the thin-film sol-gel electrolyte can be considered as stable against re-oxidation, because the long re-oxidation time of 4 hours at an operating temperature of 600 °C is unlikely to happen under real conditions.</jats:p

Microwave-Assisted CO Oxidation over Perovskites as a Model Reaction for Exhaust Aftertreatment—A Critical Assessment of Opportunities and Challenges

We introduce a microwave (MW)-assisted heterogeneous catalytical setup, which we carefully examined for its thermal and performance characteristics. Although MW-assisted heterogeneous catalysis has been widely explored in the past, there is still need for attention towards the specific experimental details, which may complicate the interpretation of results and comparability in general. In this study we discuss technical and material related factors influencing the obtained data from MW-assisted heterogeneous catalysis, specifically in regards to the oxidation of carbon monoxide over a selected perovskite catalyst, which shall serve as a model reaction for exhaust gas aftertreatment. A high degree of comparability between different experiments, both in terms of setup and the catalysts, is necessary to draw conclusions regarding this promising technology. Despite significant interest from both fundamental and applied research, many questions and controversies still remain and are discussed in this study. A series of deciding parameters is presented and the influence on the data is discussed. To control these parameters is both a challenge but also an opportunity to gain advanced insight into MW-assisted catalysis and to develop new materials and processes. The results and discussion are based upon experiments conducted in a monomode MW-assisted catalysis system employing powdered solid-state perovskite oxides in a fixed bed reactor. The discussion covers critical aspects concerning the determination of the actual catalyst temperature, the homogeneity of the thermal distribution, time, and local temperature relaxation (i.e., thermal runaway effects and hotspot formation), particle size effects, gas flow considerations, and system design

Microwave-Assisted CO Oxidation over Perovskites as a Model Reaction for Exhaust Aftertreatment&mdash;A Critical Assessment of Opportunities and Challenges

We introduce a microwave (MW)-assisted heterogeneous catalytical setup, which we carefully examined for its thermal and performance characteristics. Although MW-assisted heterogeneous catalysis has been widely explored in the past, there is still need for attention towards the specific experimental details, which may complicate the interpretation of results and comparability in general. In this study we discuss technical and material related factors influencing the obtained data from MW-assisted heterogeneous catalysis, specifically in regards to the oxidation of carbon monoxide over a selected perovskite catalyst, which shall serve as a model reaction for exhaust gas aftertreatment. A high degree of comparability between different experiments, both in terms of setup and the catalysts, is necessary to draw conclusions regarding this promising technology. Despite significant interest from both fundamental and applied research, many questions and controversies still remain and are discussed in this study. A series of deciding parameters is presented and the influence on the data is discussed. To control these parameters is both a challenge but also an opportunity to gain advanced insight into MW-assisted catalysis and to develop new materials and processes. The results and discussion are based upon experiments conducted in a monomode MW-assisted catalysis system employing powdered solid-state perovskite oxides in a fixed bed reactor. The discussion covers critical aspects concerning the determination of the actual catalyst temperature, the homogeneity of the thermal distribution, time, and local temperature relaxation (i.e., thermal runaway effects and hotspot formation), particle size effects, gas flow considerations, and system design

Characterization of the Contact Resistance of Cathodic SOFC Contacting

DC conductivity experiments were carried out in order to characterize the area specific resistances (ASR) of various multi-layer-structures. They represent the contacting interface between cathode and interconnector of state-of-the-art planar anode-supported SOFCs. The investigation focused on quantifying the influence of various chromium evaporation protection layer materials (MnOx, MnCo1.9Fe0.1O4 (MCF)), perovskitic cathode contact layers (LCC10, LCC12, LSCF), operational parameters during stack joining and the effect of pre-annealing of multi-layer samples on the overall ASR of the model system. The results demonstrate the influence of different material combinations as well as the duration of heat treatment during the joining process on the cell resistance, whereas we have not observed an obvious effect of pre-annealing.</jats:p