Thin Film Solid Oxide Fuel Cells

Contact: Daniel Beckel, Ulrich Mücke or Jennifer Rupp

In a solid oxide fuel cell (SOFC) air enters the cathode side of the cell and, after reduction, oxygen ions cross the electrolyte. On the anode side the fuel is oxidized and water is formed together with the oxygen ions. During this process heat and electricity are generated.

Today, one of the challenges in the field of SOFC is to reduce the operating temperature from the order of 950 °C to around 600 °C in order to reduce costs and to increase the reliability of SOFCs. One of the problems that has to be overcome is the lower conductivity of traditional SOFC materials (e.g. yttrium-stabilized zirconia electrolytes) at lower operating temperatures. Different materials, therefore, need to be found for that purpose. For example, gadolinium doped ceria can be used for the electrolyte, as ceria-based electrolytes show a higher ionic conductivity (sigma(i)) than zirconia-based electrolytes at lower temperatures.

For the cathode lanthanum strontium cobalt iron oxide (LSCF) is an appropriate material for low operating temperatures, since it offers both, electronic and ionic conductivity, which is needed for a cathode. In addition, LSCF offers enough catalytic activity for oxygen reduction, which is also essential for a cathode.

Besides catalytic activity towards fuel oxidation, the anode has to exhibit ionic and electronic conductivity. This can be achieved by a nickel – gadolinium doped ceria (Ni – CGO) anode.

The second important step to reduce resistance is to use thin film (around 1 micrometer) electrolytes and electrodes which can be obtained by spray pyrolysis. With this technique, the size of the fuel cell can be reduced, and therefore a micro fuel cell can be built. Such a small fuel cell could replace batteries in many applications where a longer operating time is needed. Combining high performance materials and the process of spray pyrolysis should lead to an SOFC with high power density even at low temperatures.