Thomas Franco

Progress in the Metal Supported Solid Oxide Fuel Cells and Stacks for APU

DLR is one of the pioneer groups to introduce metal supported solid oxide fuel cells (MS-SOFC) in mid 90s and it is continuing the development of the concept towards a reliable light weight 1 kW stack for APU in a funded consortium with ElringKlinger, Plansee and Sulzer Metco. The joint work is an integrated approach incorporating improved materials for functional layers, advanced industrial scale manufacturing and an evolved stack design to define a pilot production set-up for large volume manufacturing. At laboratory scale, the latest generation button cells (12 to 15 cm² effective area) exhibited more than 750 and 520 mW/cm² respectively with hydrogen and simulated reformate gas as fuel at 800°C. 2000 hours tests were performed with degradation rate of less than 1.5%/kh. Redox stability of these cells was demonstrated for 20 cycles during which the anodes were fully oxidized. Up-scaling to 85 cm² and 100 cm² effective area cells was accomplished and the cells showed 400 mW/cm² power density using simulated reformate gas at a fuel utilisation of 32%. Further improvements consisting of developing large scale industrial processes for the fabrication of functional layers including low pressure plasma spraying (LPPS) and atmospheric plasma spraying (APS) with TriplexPro are in progress. The aim is to get higher productivity and reproducibility. In addition, a new alloy for interconnects and substrates will be incorporated to further enhance the durability of cells.

Recent Development Aspects of Metal Supported Thin-Film SOFC

In recent years, the metal supported solid oxide fuel cell (MSC) technology has attained high interest for the electrical power supply in vehicles as an Auxiliary Power Unit (APU) that operates independently from the main engine. Its advantages compared with other fuel cell technologies can be seen in a higher mechanical stability and in a better thermo and redox behaviour. Those attributes are urgently needed for mobile applications.

High-velocity DC-VPS for diffusion and protecting barrier layers in solid oxide fuel cells (SOFCs)

High-temperature fuel cells of the solid oxide fuel cell (SOFC) type as direct converter of chemical into electrical energy show a high potential for reducing considerably the specific energy consumption in different application fields. Of particular interest are advanced lightweight planar cells for electricity supply units in cars and other mobile systems. Such cells, in one new design, consist mainly of metallic parts, for example, of ferrite steels. These cells shall operate in the temperature range of 700 to 800 °C where oxidation and diffusion processes can be of detrimental effect on cell performance for long-term operation. Problems arise in particular by diffusion of chromium species from the interconnect or the cell containment into the electrolyte/cathode interface forming insulating phases and by the mutual diffusion of substrate and anode material, for example, iron and chromium from the ferrite into the anode and nickel from the anode into the ferrite, which in both cases reduces performance and system lifetime. Additional intermediate layers of perovskite-type material, (e.g., doped LaCrO3) applied with high-velocity direct-current vacuum plasma spraying (DC-VPS) can reduce such effects considerably if they are stable and of high electronic conductivity.