New SOFC-Stack Design with Parallel-Connected Cells – Basic Concept and Joining Aspects†

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 parallel-connected 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.