Manufacturing alternatives for large area solid oxide fuel cells

Solid Oxide Fuel Cells (SOFC) are of great interest as energy conversion devices due to their high energy efficiency and environmentally friendly behaviour. A SOFC consists of a dense electrolyte membrane sandwiched between two porous electrodes. The most commonly used materials for this device are yttria stabilized zirconia (YSZ) for the electrolyte, a cermet Ni-YSZ for the anode and a perovskite as cathodic material. Improving the materials as well as the shaping processes of each single component is of paramount importance for obtaining devices with sufficient long-term stability at an acceptable cost. Different processes are used for the low-cost fabrication of electrodes and electrolyte for the solid oxide fuel cell, depending on which cell component is supporting the entire cell structure. The key point and major hurdle, however, is the production of a dense and thin enough electrolyte able to assure high electrochemical performances for large area cells. In the so-called anode substrate configuration, the anode is the supporting element of the cell and must therefore display sufficient mechanical stability whereas the other components of the cell are built onto it. The substrates are predominantly produced by tape casting while the electrochemical performances are enhanced depositing on its surface an anode functional layer of few micrometers. Several different techniques can be used afterwards for the electrolyte and cathode deposition. The work addresses the main issues linked to the production of a dense YSZ electrolyte layer onto a NiO-YSZ supporting anode with three of the most common (and easy scalable) ceramic deposition processes: tape casting, screen printing and wet powder spray. The influence of the nature of the deposition process on the tape formulation and thermal treatments of the green bilayer are studied and compared. An innovative lamination process at room temperature and low pressure is presented as well. All the different manufacturing methods are developed for the production of at least 5x5 cm cells.