Solid oxide fuel cell (SOFC) systems using anode off-gas and process heat for endothermic fuel reforming promise outstanding system efficiency for power generation from hydrocarbon fuels. A project team of four research institutions developed a stand-alone and thermally self-sustaining SOFC system with 830 Watt gross power and 54 % electrical system efficiency (gross, based on fuel LHV). A commercially available integrated stack module (Staxera ISM) of sunfire GmbH (Dresden, Germany) was used as SOFC.

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The TU Clausthal and CUTEC have teamed up to design, build and test a new SOFC stack architecture, based on repeating units with cells connected in parallel. This approach allows the use of electrically conducting seals like brazes and can be realized without any glass sealing. Unlike conventional (serially connected) stacks, where all cells operate at the same current but individual voltage, in this setup each cell contributes as much current as possible at a common voltage. Thereby accelerated degeneration caused by undervoltage and the associated oxidation of the nickel catalyst can be completely overcome. The concept uses two cells in electrical parallel connection with the anodes facing each other to form a repeating unit. Two designs have been realized: An all ceramic housing made from 3YSZ, sealed with reactive air brazing (RAB) and a metallic one with Crofer 22 APU housing, joined by laser beam welding.

Solid oxide fuel cells (SOFC) technology still suffers from problems like high costs and insufficient lifetime, partly caused by the traditional serial-connected stack design. To overcome some of these issues a new design with parallelconnected cells is proposed. The concept is based on a cartridge designed repeating unit consisting of two cells, electrically connected in parallel. Stack modules with 50 to 60 W can be built up by stacking and interconnect these basic units, likewise in a parallel mode. Finally, several stack modules can be connected in serial configuration to supply reasonable terminal voltage and power. Different design options for the twin cell unit were evaluated by flow field simulations and with respect to their producibility. Both, metallic and ceramic concepts for the cell frames are considered. Glass seals are completely avoided to improve durability. Reactive air brazing (RAB) is used for mounting the cells in the frames. The concept with metallic cell frames additionally uses pulsed laser welding to seal the gas compartments. Preliminary tests on welding and brazing show the general feasibility of these joining technologies and disclose a way to mass production of twin cells as basic repeating units. Flow field simulations assist the dimensioning to assure homogeneous distribution of reactants.