Fabrication and characterization of a YSZ/YDC composite electrolyte by a sol-gel coating method

The compatibility of a composite electrolyte composed of a yttria stabilized zirconia (YSZ) film and a yttria-doped ceria (YDC) substrate in a solid oxide fuel cell (SOFC) that can be operated under 800°C was evaluated. The YSZ film coated on a YDC substrate was derived from a polymeric YSZ sol using a sol-gel spin coating method followed by heat-treatment at 1400°C for 2 hr. The YSZ film deposited by spin coating showed a crack and pinhole free microstructure after heat-treatment at 1400°C for 2 hr. The absence of CeO₂-ZrO₂-Y₂O₃ was confirmed by XRD analysis. The composite electrolyte with a 2 mm thick YSZ film and 1.6 mm thick YDC substrate was deposited by six repetitive coatings then heat-treated at 1400°C for 2 hr. The open circuit voltage (OCV) of the composite electrolyte was 0.5 v higher than that of uncoated YDC electrolyte at 700°-1050°C. The maximum power density of the composite electrolyte single cell at 800°C was 122 mW/sq cm at 285 mA/sq cm. This value was lower than that of a YSZ single cell with the same thickness at 1000°C, 144 mw/sq cm at 330 mA/sq cm, but was comparable. Thus, the YSZ/YDC composite electrolyte fabricated by the sol-gel coating method was a suitable material with a high stability and comparable cell performance for low temperature SOFC operation.