Search

All solid-state batteries offer the possibility of increased safety at potentially higher energy densities compared to conventional lithium-ion batteries. In an all-ceramic oxide battery, the composite cathode consists of at least one ion-conducting solid electrolyte and an active material, which are typically densified by sintering. In this study, the reaction of the solid electrolyte Li1.3Al0.3Ti1.7(PO4)3 (LATP) and the active material LiNi0.6Co0.2Mn0.2O2 (NCM622) is investigated by cosintering at temperatures between 550 and 650 °C. The characterization of the composites and the reaction layer is performed by optical dilatometry, X-ray diffractometry, field emission scanning electron microscopy with energy dispersive X-ray spectroscopy, time-of-flight secondary ion mass spectrometry, as well as scanning transmission electron microscopy (STEM). Even at low sintering temperatures, elemental diffusion occurs between the two phases, which leads to the formation of secondary phases and decomposition reactions of the active material and the solid electrolyte. As a result, the densification of the composite is prevented and ion-conducting paths between individual particles cannot be formed. Based on the experimental results, a mechanism of the reactions in cosintered LATP and NCM622 oxide composite cathodes is suggested.

A zirconia-based potentiometric solid electrolyte gas sensor with internal solid state reference was used to study the response behavior of platinum cermet and indium tin oxide sensing electrodes. Target gases included both oxygen and carbon monoxide in nitrogen-based sample gas mixtures. It was found that with the indium tin oxide sensing electrode, the low-temperature behavior is mainly a result of incomplete equilibration due to contaminations of the electrode surface. On the other hand, some of these contaminant species have been identified as being pivotal for the higher carbon monoxide sensitivity of the indium tin oxide sensing electrode as compared to platinum cermet electrodes.

By combining results of adsorption/desorption measurements on powders and electrical conductivity studies on thick and thin films, the interaction of indium tin oxide with various ambient gas species and carbon monoxide as potential target gas was studied between room temperature and 700 &deg, C. The results show that the indium tin oxide surfaces exhibit a significant coverage of water-related and carbonaceous adsorbates even at temperatures as high as 600 &deg, C. Specifically carbonaceous species, which are also produced under carbon monoxide exposure, show a detrimental effect on oxygen adsorption and may impair the film&rsquo, s sensitivity to a variety of target gases if the material is used in gas sensing applications. Consequently, the operating temperature of an ITO based chemoresistive carbon monoxide sensor should be selected within a range where the decomposition and desorption of these species proceeds rapidly, while the surface oxygen coverage is still high enough to provide ample species for target gas interaction.

In order to be a real competitor to other industrial-scale hydrogen production technologies, solid oxide electrolysis cells (SOEC) must present essential features such as high hydrogen production rates, load flexibility and high system efficiency. However, operating conditions necessary to achieve these objectives can induce undesired performance deterioration and microstructural degradation negatively influencing the long-term stability of SOECs. This work provides the results of experimental investigations on the performance of SOECs operated under different operating conditions. In order to induce and accelerate specific degradation phenomena high steam partial pressures, fast load changes, high voltages, high steam conversion rates and alternating mode were applied. Different kinds and degrees of impact on performance and microstructure were observed and analyzed in detail. Correlations between performance changes and their underlying processes were investigated and useful connections between them were discovered. The major findings are summarized in the form of a suggestion for accelerated stress test (AST) protocols for SOECs. The developed ASTs enable deeper understanding of several degradation phenomena induced by different operating conditions and present methods for identification thereof. Further, the ASTs were estimated to have potential to predict performance changes over long-term operating periods.

The progress of the Internet of Things stimulates the development of sensors of small size and low power consumption. Miniaturized metal-oxide semiconductor (MOX) gas sensors (e.g. methane, hydrogen or carbon monoxide detection) can be integrated into agro-industrial facilities such as livestock facilities, fish farming, forestry, food-storage and horticulture, where they support future-oriented plant production (smart agriculture). The central part of a MOX gas sensor is a micro-hotplate, which is mainly responsible for the sensor power consumption at operating temperatures from 450 °C to 600 °C. Under harsh environmental conductions, ceramic materials are the best choice for the micro-hotplate substrate and sensor housing (ceramic MEMS) in combination with platinum metallization for the heater. To realize such gas sensors with low power consumption (

A new alkali-containing diopside based glass-ceramic sealant for solid oxide cells was synthesized, characterized and tested. The composition was designed to match the coefficient of thermal expansion (CTE) of Crofer22APU interconnect. The sealant has a glass transition temperature of 600 °C, a crystallization peak temperature of 850 °C and a maximum shrinkage temperature of 700 °C, thus suggesting effective densification prior to crystallization. The CTE of the glass-ceramic is 11.5 10−6 K−1, a value which is compatible with the CTE for Crofer22APU stainless steel. Crofer22APU/glass-ceramic/Crofer22APU joined samples were tested in simulated real-life operating conditions at 800 °C in dual atmosphere under an applied voltage, monitoring the electrical resistivity. The effect of two different applied voltages (0.7 V and 1.3 V) was evaluated. A voltage of 1.3 V led to a rapid decrease in the electrical resistivity during the test; such a drop was due to the formation of Cr2O3 ""bridges"" that connected the two Crofer22APU plates separated by the sealant. There was no decrease in the resistivity when a voltage of 0.7 V was applied. Instead, resistivity value remained stable at around 105 O cm for the 100 h test duration. The degradation mechanisms, due to both the alkali content and the applied voltage, are investigated and discussed.

The electrode processes governing response behavior of a solid electrolyte CO2 sensor have been studied using electrochemical impedance spectroscopy on symmetric cells exposed to various temperatures and gas compositions. It was shown that the electrochemical processes leading to potential formation at the Au/Na2CO3 electrode can be described by adapting models commonly used in the field of molten carbonate fuel cells.

The operation of solid oxide fuel cells requires gas tight and stable sealing materials. Glass ceramic materials have been established to seal different stack designs and can be optimized to match the requirements of components and joining conditions. It is known that glass based sealants are sensitive to the formation of undesired chromia species in contact with ferritic steels used as interconnects. Their formation depends on the earth alkaline type and content in the glass as well as the chromium content of the interconnect. A robust interconnect material is the chromium based sinter alloy CFY with > 93 wt.% chromium what in turn enforces the formation of chromia phases. SOFC stacks with chromium based interconnects and electrolyte supported cells (ESC) with 10SCSZ electrolyte are a candidate for SOFC systems with high efficiency in a wide power range. This study presents results on the development of sealing glasses adapted for the CFY by optimizing the glass components BaO, CaO, SiO2 and Al2O3. Depending properties like crystallization behavior, thermal expansion, adhesion and reactivity in contact with CFY have been regarded. The glasses have been tested under operating conditions of SOFC (dual atmosphere, electric potentials) in samples as well as in real stacks. It has been shown that optimized glass compositions especially regarding a limited BaO-content combine a good joining behavior and minimized BaCrO4 formation in contact with the CFY alloy.

The performances of single cell solid oxide fuel cell (SOFC) stacks with Ni/8YSZ (8 mol% Y 2 O 3 doped ZrO 2 ) and Ni/10CGO (10 mol% Gd 2 O 3 doped CeO 2 ) anodes were compared with respect to sulfur poisoning (1–50 ppm) with H 2 /H 2 O/N 2 fuel mixture at 850 °C. The mechanisms of the sulfur poisoning and regeneration of Ni/8YSZ and Ni/10CGO anodes at the triple phase boundaries are discussed. The effects of various parameters as H 2 S contamination cycles, H 2 S concentration, current density, H 2 O concentration and contamination durations were examined. A mechanism for the progress of the sulfur poisoning in the anode is proposed. It is shown that theoretically it is possible to calculate the nickel surface area accessible for the sulfur adsorption in the anode using H 2 S poisoning behavior for Ni/8YSZ anodes. The sulfur poisoning mechanisms of Ni/8YSZ and of Ni/10CGO anodes are proposed by taking into account the different oxidation mechanisms of H 2 in the anodes considered in previous studies. The higher sulfur resistance of Ni/10CGO is explained with its high mixed ionic electronic conductivity as well as its ability to adsorb H 2 . Due to these properties CGO can continue electrochemical reactions even when nickel is covered with sulfur.

Solid oxide fuel cells are the most promising power conversion units for fossil and biomass fuels combining ceramic and metallic components. Because of long-term high temperature operation and thermal cycling the standard materials cannot be applied for integration of active ceramic components. Different approaches are used nowadays for the integration of ceramic cells into stacks and of system components in the power plant. In this paper an overview on the application of glass and glass ceramic sealants, active and reactive air brazes as well as compressive mica sealants for solid oxide fuel cells is made. The crystallizing glasses are more favorable for cell integration in the stack for operation in a broad temperature range. Metallic brazes are mainly limited to integration of anode or metal supported cells in ferritic alloy gaskets for operation at T

Solid oxide fuel cells are the most promising power conversion units for fossil and biomass fuels combining ceramic and metallic components. Because of long-term high temperature operation and thermal cycling the standard materials cannot be applied for integration of active ceramic components. Different approaches are used nowadays for the integration of ceramic cells into stacks and of system components in the power plant. In this paper an overview on the application of glass and glass ceramic sealants, active and reactive air brazes as well as compressive mica sealants for solid oxide fuel cells is made. The crystallizing glasses are more favorable for cell integration in the stack for operation in a broad temperature range. Metallic brazes are mainly limited to integration of anode or metal supported cells in ferritic alloy gaskets for operation at T

Planar solid oxide fuel cells (SOFC) are considered to be power generators with high efficiency and low emission at small power units (1-200kWel). Many prototype systems are already successfully realized. For mass production the costs have to be reduced and the long-term stability has to be enhanced. Power losses less-than 0.5%/1000h is the target value for stacks in stationary SOFC-based power systems. To reach this goal, the factors influencing degradation have to be found and reduced. In this work the interaction between interconnect and different ceramic materials such as perovskites (La0.8Sr0.2(Mn,Co)O3, La0.65Sr0.3MnO3, La0.65Sr0.3(Mn,Co)O3) and spinels (Mn(Co,Fe)O4, (Cu,Ni)Mn2O4) was investigated on the cathode (air) side of conventional ferritic interconnect materials (CroFer22APU, ITMLC, ZMG232L). The method to determine the value of the area specific resistance between interconnect and contact layer (R ICC) within a tolerance of 10% has been developed to provide reliable data for ASR values and their degradation.The R ICC-value increases with annealing time. The degree of this increase depends on used materials and their combination. The spinel contact layers form a thin dense ceramic layer at the beginning of the annealing process. This layer reduces the oxidation rate of the alloy. Because of this protection layer a thinner oxide scale grows and the ASR aging rate is much lower (0.4-0.9m Omega cm2/1000h). The comparison of the aging rates of different alloys with La0.8Sr0.2(Mn,Co)O3 contact layer reveals remarkable differences: 3.1m Omega cm2/1000h for CroFer22APU, 10.9m Omega cm2/1000h for ITMLC and 21.2m Omega cm2/1000h for ZMG232L.The degradation in a stack has been determined from the R ICC-values and geometric factors. The impact of oxidation at the cathode side of interconnect is about one third of the total stack degradation. The method opens the possibility for comparing area specific resistances of special material combinations with high accuracy. By optimized material combinations the degradation in stacks can be reduced to less-than 0.5%/1000h.

Corrosion kinetics of ferritic alloys/steels (Crofer22APU, ITMLC, ZMG232L) were studied at high temperature. An extent of corrosion was evaluated by measuring the oxide scale thickness and the weight gain as a function of heating time. It is shown that even porous layer applied to interconnect can significantly reduce the rate of the steel oxidation. Contribution of the “oxide component” into the total degradation of the SOFC stack performance is estimated. Different protection materials and combinations were tested to analyze their influence on the processes of high temperature oxidation and long-term degradation of Fe-Cr steels. It has been shown that “more soft” materials on the basis of spinels (Mn(Co1 − x Fe x )2O4, Cu1 − x Ni x Mn2O4) are most suitable materials for the use as protective layers in comparison to perovskites. The efficiency of different protective materials was also tested in the real SOFC stacks designed in cooperation with company Staxera GmbH. It has been shown that applied spinel materials can effectively increase the long-term stability of the SOFC stacks.