Fabrication and characterization of tubular solid oxide fuel cells

Abstract

Processes to fabricate tubular solid oxide fuel cells (SOFCs) using various electrolyte and electrode materials have been investigated. Single-phase perovskite strontium- and magnesium-doped lanthanum gallate (LSGM) was synthesized. Mechanical and thermal properties, and the cell performance of LSGM electrolyte fuel cells were studied and compared with yttria-stabilized zirconia (YSZ) electrolyte systems. Paste extrusion was identified as a suitable method for high-speed manufacture of the tubular support components. Procedures were developed to extrude dense, straight, round (OD: 2-4 +/- 0.1 mm), thin-walled (0.2 +/- 0.02 mm) tubular LSGM and YSZ electrolytes, and porous anode or cathode support (5-20 mm OD, 0.5-2 mm wall thickness). The research systematically investigated developing a fabrication process, designing the extrusion die, the effects of formulation and process additives, and how to handle, dry, and sinter the extrudate. Dip coating, brush painting, vacuum infiltration, electrophoretic coating, and plasma spray were examined for applying thin films on the tubular support. The average three-point bending strengths of extruded and sintered LSGM were determined to be 287, 195, 184, and 147 MPa at room temperature, 600 degrees C, 800 degrees C, and 1000 degrees C, respectively. Room-temperature burst strengths (average) of the tubular electrolytes made from YSZ and LSGM were 127 and 40 MPa, respectively. Room-temperature bending strength and burst strength (average) of the as-sintered NiO-YSZ anode were 300 and 100 MPa, respectively. The average thermal expansion coefficients of YSZ and LSGM were 10.18 x 10(-6)/degrees C and 11.01 x 10(-6)/degrees C, respectively, between room temperature and 800 degrees C. The maximum power density at 800 degrees C for a 220-mu m-thick LSGM electrolyte was 460-482 mW/cm(2), which is more than double the power density for YSZ cells (200-220 mW/cm(2)) at 850 degrees C. Reducing LSGM thickness from 550 to 220 mu m increased the maximum power densities by more than 30%. Repeatable cell power outputs per cell of 2.5 W at 800 degrees C and 2.8 W at 850 degrees C were obtained. The cell durability was evaluated during a 500-h test. This comprehensive study intended to better understand the relationship between the materials, processing, manipulation of the microstructure, properties, and tubular SOFC performance.