Hyun Jun Ko

Improvement of Open Circuit Voltage (OCV) depending on Thickness of GDC Electrolyte of LT-SOFCs

It has been considered to apply GDC (Gd 0.1 Ce 0.9 O 1-X ) for low-temperature SOFC electrolytes because it has higher ionic conductivity than YSZ at low temperature. However, open circuit voltage with using GDC (Gd 0.1 Ce 0.9 O 1-X ) electrolyte in SOFCs, becomes lower than using YSZ (8 ㏖% Yttria stabilized Zirconia) electrolyte because GDC has electronic conductivity. In this work, the effect of changing GDC electrolyte thickness on the open circuit voltage has been investigated. Ni-GDC anode-supported unit cells were fabricated as follows. Mixed NiO-GDC powders were pressed and pre-sintered at 1200℃. And then, GDC electrolyte material was dip-coated on the anode and sintered at 1400℃. Finally the LSCF-GDC cathode material was screen-printed on the electrolyte and sintered at 1000℃. Electrolyte thickness was controlled by the number of dip-coating times. Open circuit voltage was measured depending on electrolyte thickness at 650℃ and found that the thicker GDC electrolyte was, the better OCV was.

Structural Stability of the GDC Electrolyte for Low Temperature SOFCs Depending on Fuels

It has been considered to apply Od 0.1 Ce 0.9 0 1―x (GDC) to low temperature solid oxide fuel cell (SOFC) electrolytes at a low temperature. However, ceria cannot be efficiently used with hydrogen and wet hydrocarbon fuels because its structure change Ce4 + → Ce 3+ ) causes a decline of mechanical strength under a reducing atmosphere. In this work, the structural stability test of the GDC electrolyte was investigated under H 2 and dry CH 4 atmospheres depending on the fuels at 650°C. This study clearly confirmed from the scanning electron microscopy, X-ray photoelectron spectroscopy, and mechanical strength data that many more Ce 4+ ions transform into Ce 3+ ions under the reducing (H 2 ) atmosphere [J. Alloys Compd., 408―412, 628 (2006); Solid State Sci., 7, 539 (2005)].