Production and Characterization of Micro-Tubular Solid Oxide Fuel Cells

In the present work, micro-tubular solid oxide fuel cells μt-SOFCs) constituted by NiO/YSZ anode with an embedded current collector, YSZ as electrolyte, YSZ/LSM as functional cathode layer and pure LSM as cathode current collector layer were fabricated by dip-coating technique. The fuel cell was designed according to the anode-supported configuration with a metallic coil introduced within the anode during the cell fabrication. The production of the devices through wet colloidal process required the optimization of suspensions employed for the dip-coating. Then, investigation on rheological properties for the anode and electrolyte water-base slurries was carried out with particular emphasis to the solid loading and the concentration of slurry additives as well as temperature. In addition, thermal analyses elucidated the response of anode, electrolyte and cathode layers during drying, binder burn-out and sintering processes. The thermal behaviour of pyrolisable materials and oxidation of the metal components used as current collector was performed using conditions identical to cell fabrication like temperatures as high as 1400°C in oxidative atmosphere. After sintering, the complete μt-SOFCs with embedded current collector were produced with outer diameter as low as 1.0 mm and length of 30 mm with an effective active cathode length of 20 mm resulting in an active area of 0.63 cm2. The cell performance was analyzed by V-j plots in the temperature range of 700-800°C where the effect of the cell diameter and current collector characteristics on power density was pointed out. The efficiency of current collector was examined by comparing coils with different configurations (turns per unit length) as well as nature of the metal. The cell performance was demonstrated to be related to the current collector configuration. In particular, as twice the turns per unit length are as double the current density is, thus making the power density 4-fold. An additional improvement of the cell performance was found for the palladium current collector where the power density was increased by a factor more than 4 in comparison with the cell made with nickel collector due to the higher catalytic activity of palladium for electrochemical reactions. On the basis of these findings, a further development of μt-SOFCs with embedded collector was suggested with an alternative design of palladium current collector for which an estimate of power density of micro-tubular cell provided values higher than 0.7 W/cm2 at temperature of 800°C.