Detailed insight into electrochemical reaction mechanisms and rate limiting steps is crucial for targeted optimization of solid oxide fuel cell (SOFC) electrodes, especially for new materials and processing techniques, such as Ni/Gd-doped ceria (GDC) cermet anodes in metal-supported cells. Here, we present a comprehensive model that describes the impedance of porous cermet electrodes according to a transmission line circuit. We exemplify the validity of the model on electrolyte-supported symmetrical model cells with two equal Ni/Ce0.9Gd0.1O1.95-δ anodes. These anodes exhibit a remarkably low polarization resistance of less than 0.1 Ωcm2 at 750 °C and OCV, and metal-supported cells with equally prepared anodes achieve excellent power density of >2 W/cm2 at 700 °C. With the transmission line impedance model, it is possible to separate and quantify the individual contributions to the polarization resistance, such as oxygen ion transport across the YSZ-GDC interface, ionic conductivity within the porous anode, oxygen exchange at the GDC surface and gas phase diffusion. Furthermore, we show that the fitted parameters consistently scale with variation of electrode geometry, temperature and atmosphere. Since the fitted parameters are representative for materials properties, we can also relate our results to model studies on the ion conductivity, oxygen stoichiometry and surface catalytic properties of Gd-doped ceria and obtain very good quantitative agreement. With this detailed insight into reaction mechanisms, we can explain the excellent performance of the anode as a combination of materials properties of GDC and the unusual microstructure that is a consequence of the reductive sintering procedure, which is required for anodes in metal-supported cells.

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La 0.58 Sr 0.4 Co 0.2 Fe 0.8 O 3-δ (LSCF) cathodes on metal-supported solid oxide fuel cells (MSCs) were fabricated by a novel sintering approach and electrochemically tested in single-cell measurements. The sintering of cathodes on complete cells was performed under argon atmosphere at 950 • C in order to prevent strong oxidation of the metallic support. During this sintering process, a phase decomposition of LSCF occurred, which was found to be reversible upon heating in ambient air. The observed performance increase of MSCs with cathodes sintered ex situ, compared to cells processed under standard conditions, revealed a beneficial effect of the increased sintering temperature on cell performance. At 750 • C and 0.7 V a current density of 0.96 A/cm 2 was achieved. A stronger adherence of the cathodes sintered ex situ was observed after single-cell measurements. In additional experiments, La 0.58 Sr 0.4 CoO 3-δ (LSC) was applied as an alternative cathode for MSCs. These cells were activated in situ at 850 • C due to the lower thermochemical stability of LSC and indicated potential for further improvement of the cell performance. The successful electrochemical characterization of the cells with LSCF cathodes sintered ex situ confirmed the applicability of the novel sintering procedure as well as the improved adherence achieved by the optimized processing.

Cathode processing is one of the main challenges in the manufacturing of metal-supported solid oxide fuel cells (MSCs). Cathode sintering in ambient air is not applicable to MSCs, as oxidation of the metal substrate and the metallic Ni of the anode damages the cell. A recently developed ex situ sintering procedure for the LSCF cathode in an argon atmosphere was shown to significantly improve cathode adherence. However, the stability of the sintered cathode layer posed a challenge during storage in ambient air. In the present work, adapting the ex situ sintering approach to LSC/GDC dual-phase cathodes not only enabled the ex situ sintering process to be applied to LSC-based cathodes, but also resulted in the superior stability of the cathode after sintering. Despite the hygroscopic properties of the partially decomposed perovskite, LSC/GDC dual-phase cathodes were shown to withstand more than 1 year of storage in ambient air without failure. Electrochemical single-cell measurements and post-test analysis confirmed the reversibility of phase transformations and the electrochemical activity of such dual-phase cathodes. Current densities of 1.30 A cm −2 at 750°C, 0.85 A cm −2 at 700°C, and 0.54 A cm −2 at 650°C were obtained at a cell voltage of 0.7 V.

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To demonstrate the performance and reliability of MSCs (Metal Supported SOFCs), a systematic electrochemical characterization on button cells has been performed. The cell conditioning during the first heating-up is described in detail, since there is a significant difference to ESCs (Electrolyte Supported Cell) and ASCs (Anode Supported Cell). The focus of the present work is to show the influence of different anode materials, gas-flow rates, and operation temperatures on recorded i-V-curves. In some cases, fuel utilization rates were used, which are higher than commonly applied in button cell experiments. However, under these harsh conditions, the anode and the metal substrate must handle e.g. high humidity. This paper summarizes recent results on (i) manufacturing, (ii) appropriate test procedures, (iii) electrochemical testing, and (iv) influence of different anode layer materials for MSCs.

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Metal-supported solid oxide fuel cells (MSCs) are promising candidates for non-stationary applications like auxiliary power units (APUs) in heavy duty trucks or range extender systems for battery electric vehicles. Due to limited space available for integrating such systems especially in passenger cars, achieving high power density of MSCs is essential. The MSC concept of Plansee, Austria was stepwise optimized by improved processing of the electrodes and tailoring of the interfaces. Variations of cathode composition and sintering conditions were investigated. Using LSC or LSC/GDC cathodes and Ni/GDC anodes with higher electrochemically active volume increased the cell performance significantly. Moreover, reducing the electrolyte to 2 µm resulted in further improvement of the performance. Finally, preliminary results of long-term operation of the Plansee MSC for more than 1.000 h at 700 °C and 300 mA cm-2, as well as post-mortem analyses, are presented.