Innovative flexible SOFC stack concept
We present a SOFC stack technology based on the unique SOFConnex™ concept. It uses flexible gas distribution layers between metal sheet interconnects and thin ASE cells (Ni-YSZ anode supported, thin electrolyte). Flexibility is given both in material and design. The interlayer absorbs cell imperfections, facilitates gas feeding, and shows a current collection density superior to other approaches. New configurations are rapid to implement and test, manifolding can be internal, external or combined, and sealing is simplified. In combination with the thin components, the SOFConnex™ stacking concept allows compact assembly of stacks with low cost potential and adequate power density. Presently three different flow designs are being developed, illustrating the flexibility of the concept. With the standard flow configuration, multiple cell stacks were assembled and tested. Power density at start-up for 7 stacks (composed of 5 cells) is given in the figure (800°C = maximum local temperature, H2 fuel at a feed of 5 ml/min.cm2, lair = 1.6). Considering variable temperature distributions, and the facts that the ASE cells originate from 5 different fabrication batches and that 2 different metal interconnect types are used, reproducibility of the performance is fair. After 4-5 days of operation, marked by an important performance increase, power density reaches 0.5 W/cm2 at 0.7 V average cell voltage (1.5 kWe/L), for 65% fuel utilisation and 35% LHV electrical efficiency (fuel feed 8 m/min.cm2). Behaviour with syngas fuel and reformed biogas fuel will be reported. Results from the other two designs under development, and their differences with respect to the standard design, will be shown and discussed.