5555.1:
Nanodispersions for low temperature sintering of thin film SOFC electrolytes
Abstract
Nanostructured ceramics might show attractive features, such as superplasticity, diffusion bonding and high fracture toughness. At present only a few such structures have been produced due to the difficulty of working with nanopowders. A challenge in the use of nano-particles to produce high quality, high performance ceramics is still to achieve high solid loaded dispersions of nanoparticles and subsequent processing of the dispersions.
The use of nanopowders in coatings and films is advantageous, because the sintering temperature can be lowered and fine scale structures can be produced. Significant technological benefits are expected by the application of nanoscale powders for solid oxygen fuel cells (SOFC). The structural integrity of the present Sulzer Hexis SOFC PEN technology (PEN= cell consisting of cathode, electrolyte and anode) is given by a 150 m thick zirconia electrolyte. The electrolyte thickness constrains the cell efficiency due the ohmic resistance. Therefore, efforts are currently being made in the development of anode supported electrolyte cells (ASE) at Sulzer Innotec as next generation cells for the Sulzer HEXIS SOFC system. The major technical advantage of the ASE PEN lies in the potential for a electrolyte thickness reduction down possibly to a 5 to 10 m zirconia layer. Furthermore, this layer could be produced using cost-effective processes such as screen printing, electrostatic spraying or others. However, the development of a nanodispersion technology is needed for two reasons. At first, a reduced sintering temperature is desired for densification of zirconia based electrolytes when it is combined with certain electrode materials. Otherwise, electrically insulating barriers would be generated at conventional sintering temperatures. A sintering temperature reduction is expected when highly sinter active nanoscale powders are used as electrolyte materials. Secondly, a lower sintering temperature is beneficial to achieve an adjustment of theshrinkage of the electrodes and the electrolyte layer during co-sintering.
This project constitutes research in dispersion technology for nano-powders. Thin electrolyte films, formed by processing of nano-dispersions, are needed from industrial point of view in order to lower the sintering temperature in the manufacturing of anode supported electrolyte (ASE) SOFCs. The concept of the application of nano-dispersed slurries for manufacturing of thin solid electrolytes for ASE cells, will be investigated using preferably screen printing as deposition technique. Improvements will be evaluated in terms of avoidance of pinhole and crack formation in the electrolyte.