Electrochemical performance and interfacial reaction of LSCF-GDC composite cathode on GDC/ScSZ bilayer electrolyte for IT-SOFCs

초록

There has been considerable interest in intermediate temperature solid oxide fuel cells. When the operating temperature of SOFCs would be reduced to 500~800℃, one can use much cheaper and more durable stainless steel interconnector than lanthanum chromites, resulting in the production of SOFC stacks with cost-performance and high reliability. However, the overpotential due to the electrode, mainly, cathode polarization and electrolyte ionic resistance are steeply increased with decreasing the operation temperature. An electronic conducting LSM, which is known to be the best cathode material for an YSZ electrolyte, should be replaced by mixed ionic and electronic conducting materials such as LSCO, La0.6Sr0.4Co0.2Fe0.8O3-δ(LSCF), and so on. In addition, Gd2O3-doped CeO2(GDC), Sc2O3-stabilized ZrO2(ScSZ), and strontium magnesium doped lanthanum gallate(LSGM) is expected to be an attractive electrolyte because of their higher ionic conductivity than the YSZ. In order to apply the LSCF as a cathode and ScSZ as an electrolyte for intermediate-temperature SOFCs, a GDC buffer layer was inserted between the cathode and electrolyte. It was confirmed that the GDC buffer layer could prevent unfavourable solid-state reactions at the LSCF/ScSZ interfaces. The GDC buffer layer was deposited on the ScSZ electrolyte by two different methods; a screen-printing and pulsed-laser deposition (PLD) process. The screen-printed GDC buffer layer showed a porous microstructure, while a dense GDC layer could be obtained by the PLD process. A porous LSCF cathode prepared on a thin and dense GDC buffer layer exhibited excellent electrochemical performance even at 600℃. Dispersing GDC or Pt small particles into the LSCF cathode enhanced the performance further.