Improvement of Electrochemical Performance of Thin Film Mixed Ionic Electronic Cathode for Low Temperature Solid Oxide Fuel Cells By Additional Catalytic Current Collecting Layer

Abstract

In the present study, catalytic current collecting layer (CCCL) was added to thin film La0.6Sr0.4Co0.8Fe0.2O1-δ (LSCF) cathode for low temperature solid oxide fuel cells (LT SOFCs) to improve both electrical current collection and catalytic activity. By adding CCCL, the maximum power density improved nearly 10-fold compared to the bare LSCF cathode. With thicker Pt or Pd CCCL, ohmic loss in current collection and oxygen reduction reaction (ORR) activity were both improved. Due to smooth oxygen ion conduction of solid oxide electrolytes, a typical range of operating temperature of SOFCs is 800 ~ 1000 ℃, which imposes a number of obstacles for SOFCs to be commercialized. Lots of studies have been carried out to make the operating temperature lower, down to 400 ~ 600 ℃. However, not only ion conduction in electrolytes but also ORR activity in cathode highly depends on temperature. As the operating temperature goes down, the faradaic impedance of SOFCs become severe because of sluggish ORR at a lower temperature. LSCF, one of the widely used cathode material in SOFCs, shows poor ORR activity and electronic conductivity at this temperature range. Therefore, Pt has been mainly used as electrode material for LT SOFCs based on its superior catalytic activity in lower temperature but it suffers from thermal instability, such as agglomeration. In this report, the noble catalysts, Pt and Pd, were investigated as the CCCL for mixed ionic electronic conductor LSCF cathode to enhance both electronic conductivity and catalytic activity at 550 ℃. LSCF cathode was deposited on the single crystal (100) YSZ pellet by using PLD. For the CCCL, Pt and Pd were adopted and deposited via direct current (DC) magnetron sputtering on the LSCF cathode. The thickness of the CCCL was varied from 100 nm to 300 nm. Ni was used as anode and deposited on the other side of the pellet via DC magnetron sputtering for about 300 nm. GDC interlayer with thickness of approximately 250 nm was applied between YSZ pellet and LSCF cathode to block formation of any insulation layer through reaction between YSZ and LSCF. Electrochemical performance was investigated through i-V plot and EIS and long-term stability was measured with Galvanostatic mode. The microstructure of LSCF and CCCL were investigated through FIB-SEM, FE-SEM. Crystal structure of the LSCF cathode CCCL was studied with XRD.