Application of the residue number system to the matrix multiplication problem

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Charakterisierung und Optimierung der Grenzfläche Elektrolyt/Kathode in metallgestützten Festelektrolyt-Brennstoffzellen

Metal-supported solid oxide fuel cells (MSC) offer various advantages compared to full ceramic cells. Low-cost materials and high mechanical ruggedness make MSCs the fuel cell of choice for mobile applications, such as auxiliary power units for heavy duty vehicles or range extender modules for battery electric passenger cars. However, MSC-specific degradation phenomena occur, as the processing has to be adapted to the porous metal substrate. For example, the La$_{0,58}$Sr$_{0,4}$Co$_{0,2}$Fe$_{0,8}$O$_{3-\delta}$(LSCF) cathode of the state-of-the-art Plansee MSC is in situ activated at 850 °C,which differs considerably from the established cathode sintering at 1040 °C for anode supported cells. As a result, the cathode adherence on the Ce$_{0.8}$Gd$_{0.2}$O$_{2-\delta}$ diffusion barrier and long-term stability during operation are insufficient. The aim of the present work is to increase the long-term stability of the LSCF cathode by improving the adherence strength of the cathode layer. Moreover, an increase of the cell performance is of interest from an industrial point of view, in order to lower system weight and volume. Three approaches were considered: i) development of an ex situ sintering procedure for complete MSCs under controlled atmosphere in combination with an increased sintering temperature; ii) improvement of the cathode adherence after in situ activation by optimizing the activation conditions or cathode raw material; and iii) implementation of alternative cathode materials like La$_{0,5}$8Sr$_{0,4}$CoO$_{3-\delta}$ (LSC) in order to increase cell performance. Increased sintering activity and adherence strength were observed by dilatometry and adhesive tape test, when increasing the sintering temperature to T ≥ 950 °C. Ex situ sintering of MSCs under argon atmosphere caused phase decomposition of the cathode material. The reversibility of this phase decomposition was confirmed by ambient temperature as well as high-temperature XRD. Full re-oxidation to single phase perovskite takes place at T ≥ 750 °C during the heat-up and sealing procedure prior to cell operation, without damaging the cathode layer. Cells utilizing Ni/YSZ anode and LSCF cathode sintered ex situ delivered improved cell performance of 1.4 A/cm$^{2}$ at 785 °C and 0.7 V. 1500 h of continuous operation (300 mA/cm²,700 °C), without any degradation, confirmed the long-term stability. Implementationof LSC cathodes resulted in increased cell performance. 700 h of operation at 300 mA/cm$^{2}$ and 700 °C did not reveal any degradation of a cell consisting of Ni/YSZanode and LSC cathode activated in situ at 850 °C. Promising low-temperature performance of 0.8 A/cm$^{2}$ at 600 °C and 0.7 V was achieved by utilizing LSC cathodeon cells with Ni/GDC anode. As a further development, LSC/GDC dual-phase cathodes were applied using the ex situ sintering approach. This cathode type not only revealed improved layer stability during storage but also provided high electrochemical performance of 1.3 A/cm$^{2}$ at 750 °C and 0.7 V, despite nonoptimized microstructure. The overarching conclusion is that cathodes sintered ex situ provide significantly improved long-term stability as well as high electrochemical performance during MSC operation. Optimization of the microstructure of dual-phase cathodes offers further potential to improve cell performance

Charakterisierung und Optimierung der Grenzfläche Elektrolyt/Kathode in metallgestützten Festelektrolyt-Brennstoffzellen

Metallgestützte Festoxidbrennstoffzellen (MSC) bieten vorteilhafte Eigenschaften für mobile Anwendungen gegenüber vollkeramischen Konzepten. Als MSC spezifische Degradationserscheinung tritt eine geringe Langzeitstabilität der La$_{0,58}Sr_{0,4}Co_{0,2}Fe_{0,8}O_{3}$-$\delta$ (LSCF) Kathode aufgrund mangelnder Haftfestigkeit auf der Diffusionsbarriere auf. Zur Optimierung der LSCF Kathode auf MSCs wurden drei Arbeitsansätze definiert: i) Entwicklung eines "ex situ" Sinterprozesses, zur Sinterung kompletter Zellen vor dem Betrieb; ii) Verbesserung der nach in situ Aktivierung erreichten Haftung und iii) Einführung alternativer Kathodenwerkstoffe wie $La_{058}Sr_{0,4}CoO_{3}$-$\delta$ (LSC), mit dem Ziel der Leistungssteigerung. Anhand der ermittelten Sintereigenschaften und Phasenstabilität der Kathodenwerkstoffe in Abhängigkeit von Temperatur und Atmosphäre wurden geeignete Parameter für die Zellherstellung gewählt. Mittels elektrochemischer Einzelzellmessungen wurde die Leistungsfähigkeit dieser Zellen nachgewiesen

Performance Benchmark of Planar Solid Oxide Cells Based on Material Development and Design.

Solid oxide cell (SOC) technology currently attracts great attention due to its unique potential for substantially contributing to a carbon‐neutral power supply. The variety in possible designs and applications—covering oxygen ion and proton conductors and the ability to convert surplus electricity to easily storable synthetic fuels, as well as to produce electricity from these fuels according to demand and availability—provides the excellent position of SOCs with regard to decentralized power generation and distribution. Herein, a reference work on cell performance is provided by highlighting specific advantages of the different cell types, designs, and materials with regard to certain operating conditions, including challenges concerning operational modes, processing, and degradation. In conjunction with a critical examination in terms of relevance and technical feasibility, the data provided enable an assessment of the general potential of the cell types for technology development and connect scientific research to industrial considerations

Material development for operation of solid oxide cells under specific conditions

Development of solid oxide cells (SOC) over several decades has led to substantial enhancement of the cell performance and a profound understanding of degradation mechanisms. Moving past the basic limitations caused by design, processing and microstructural issues, it becomes clear that further progress requires application-oriented research activities and cell designs. The optimum material combinations and microstructure of a cell is likely to differ depending on operational mode, intended operation temperature and lifetime as well as between stationary and mobile application. According to these boundary conditions, various research topics have been tackled at Forschungszentrum Jülich. On the basis of the well-known anode-supported cell (ASC) concept, electrode development and optimization of the electrolyte layer was performed aiming at low-temperature operation (<600°C). By implementation of a GDC electrolyte, for example, the ohmic resistance was reduced by more thana factor of 3. Investigation of highly active Ni/GDC cermets as fuel electrode are another topic of investigation. First progress achieved on metal-supported cells can be transferred for ongoing work to further increase low-temperature performance of ASCs. The material development is aided by electrochemical testing of symmetrical cells and full-cells and supported by theoretical considerations of the materials elementary properties. (For details please refer to Christian Lenser et al., Performance analysis of a planar solid oxide fuel cell stack between 750 °C and 500 °C, J. Power Sources 474 (2020), 228671, https://doi.org/10.1016/j.jpowsour.2020.228671, and David Udomsilp et al., Metal-Supported Solid Oxide Fuel Cells with Exceptionally High Power Density for Range Extender Systems, Cell Reports Physical Science 1 (2020), 100072, https://doi.org/10.1016/j.xcrp.2020.100072