Tuesday, 25 July 2017
Grand Ballroom East (The Diplomat Beach Resort)
Since many years solid oxide fuel cells (SOFCs) are used in stationary systems, in a range from 0.1 up to 1,000 kW, to generate electric power or combined heat and power (CHP). For these applications, electrolyte or anode supported cells (ESCs, ASCs) are the preferred SOFCs and have been demonstrated in different installation environments. In the last years lots of research has been done on metal supported solid oxide fuel cells (MSCs) for mobile applications e.g. auxiliary power units (APUs) or range extenders. For this type of cell, a powder-metallurgically manufactured metal substrate (e.g. Fe26Cr) works as backbone of the cell. This substrate is highly porous and its coefficient of thermal expansion (CTE) matches quite well with the commonly used 8YSZ (8 mol% Y2O3 fully stabilized ZrO2) ceramic electrolyte material. This adopted CTE avoids cracks within the electrolyte layer during heating-up and cooling-down procedures as well as the operation itself. Besides, the ductile substrate together with the thin electrolyte is very robust against vibrations. The anode is applied onto the metal substrate via screen printing and sintering and consists of porous Ni/8YSZ, which is a very well-known SOFC anode material. The anode reduces the pore size of the coarse porous metal substrate by more than one order of magnitude and enables the thin electrolyte to gas-tightly separate the porous anode from the cathodic side. The electrolyte (8YSZ) is rather thin being applied by a special PVD-process, a gas flow sputtering process. Compared to ESCs or ASCs, this thinness enables lower operation temperatures, which is advantageous for mobile applications. Lastly, the cathode is applied via screen printing and consists of porous LSCF (La0.6Sr0.4Co0.8Fe0.2O3-δ), which is also well-known in the SOFC community.
To show the performances and reliabilities of MSCs, a series of electrochemical characterizations on button cells were performed. The cell conditioning during heat-up will be described as it is slightly different to that of ASCs and ESCs. The main focus of this proceeding is to show the influence of gas-flow rates, gas compositions and operational temperatures on recorded i-V-curves. To do so, some of the testing parameters work at high fuel utilization rates, which is not commonly used for button cell experiments. However, with this parameters, it was interesting to see, how the anode and the metal substrate handle high humidity. Furthermore, significant performance improvements with recently developed anodes and cathodes will be presented.
To sum up, this conference proceeding gives an overview on (i) manufacturing, (ii) appropriate test procedures, and (iii) electrochemical testing of MSCs.