SOFC stack development

The performance at 1000 deg. C is similar to the performance of the state-of-the-art Ni-YSZ anode i hydrogen. Carbon deposition does not occur even at low steam to carbon ratios with methane fuel. The anode has been demonstrated in 5x5 cm cells and will be explored further in projects under EU's Framework V program, because it has demonstrated stability under as well redox situations as during temperature cycling. A sintering aid for the Ni-YSZ anode has been developed, and a patent is pending. The sintering aid reduces the polarisation resistance at 800 deg. C by a factor of 3, increase the in-plane conductivity by a factor of 20-25 and reduces the undesired high catalytic activity of Ni towards steam reforming to an acceptable level. A model study concerning stack design optimisation has been carried out. The study identifies suitable steam reforming rates taking into account the mechanical integrity of the stack (minize internal stress) and maximising overall performance (power density, fuel utilisation and excess of air). A partial model for internal reforming in Ni anodes may be used to convert the above acceptable reaction rates to electrode thickness. High-temperature mechanical data have been collected for the LSCV interconnect material. The influence of dimensional criteria upon interconnect component stability has been investigated based upon a fracture mechanical model. A fracture mechanical analysis has also been made on electrolyte materials. A study has been made of the importance of grading materials compositions in interconnects, electrodes and electrolyte supports as a basis for development of new electrodes and electrode supported thin electrolyte cells. Since June 1997 development of an anode supported thin electrolyte cell has been carried out in the EFP96, EFP97 and EFP98 SOFC projects. The development is therefore described in all the projects. This development reached the first primary target at the end of 1998 by the demonstration of an internal resistance of 0.4OMEGA.cm2 at 850 deg. C for 5x5 cm cells. Simultateously the cost of production has been minimized further by enabling contiuous wet ceramic processing of the combined anode and electrolyte element with a single cofiring operation. Patenting is attempted in 1999