Transition metal-doped yttria stabilized zirconia for low temperature processing of planar anode-supported solid oxide fuel cell

An attempt has been made to reduce the processing temperature for fabrication of anode-supported solid oxide fuel cell using transition metal doped 8 mol% yttria stabilized zirconia (YSZ) as the material for electrolyte and Ni-YSZ anode support. Through a simple mixing technique, the sintering temperature of a widely used commercial YSZ powder is possible to reduce substantially by adding 2 mol% transition metal oxides e.g. cobalt, manganese and iron. More than 96% of theoretical density is achieved at 1175 degrees C. No difference in thermal expansion behaviour is observed for the doped YSZ with respect to pure YSZ (without any additive). Using tape casting and lamination techniques, planar anode-supported half cells (Ni-YSZ/YSZ) were fabricated with such doped YSZ and co-sintered at two different temperatures viz., 1175 degrees C and 1350 degrees C. Finally, single cells (dia. similar to 15 mm) were fabricated through screen printing of La(Sr)MnO3 (LSM)-YSZ based cathode active layer and LSM current collector layer and tested with hydrogen as fuel and oxygen as oxidant in the temperature range 700-800 degrees C. A reasonably good electrochemical performance (similar to 1.6 A/cm(2) at 0.7 V and 800 degrees C) is achieved for single cells when half-cell sintering temperature is 1350 degrees C. However, under identical conditions, the current density dropped below 0.2 A/cm(2) when the corresponding half-cell is sintered at 1175 degrees C. For such a cell, although the open circuit voltage (OCV) is found to be very stable (similar to 1.1 V), the current drawing capability fell abruptly with increasing current load and a corresponding decrease of cell voltage. The cell microstructure revealed that while sintering half-cell at 1175 degrees C, complete densification of the doped YSZ electrolyte film is not achieved. It is anticipated that redesigning of fabrication steps could be required to utilize the benefits of low sintering temperature of cell components. (C) 2014 Elsevier B.V. All rights reserved.