Development of Thin Film Single Chamber Solid Oxide Fuel Cell Using Nano-Dendritic Ru-GDC Anodes

Abstract

Fuel cells are energy conversion device which directly converts chemical energy into electric energy. Since it has no moving parts, high reliability and continuous conversion is guaranteed. However, conventional fuel cells have too high or low operating temperature due to the characteristics of electrolyte materials. To solve the temperature issue of fuel cells, high temperature (800oC>) operating solid oxide fuel cell was operated at intermediate temperature between 500~600oC. Intermediate temperature operation of solid oxide fuel cell has advantages of allowing cheap stainless steel components and improved system stability. Additionally, to solve the problem of hydrogen storage and inefficient production, we directly operated fuel cell with hydrocarbon fuels without reformers. It requires advanced anode and cathode structure and material. To verify the application of thin film for SOFCs, we used sputtering to fabricate metal and ceramic nano-composite electrodes. We analyzed morphological and electrochemical data by different ratio of metal and ceramic composite films. The porosity and grain size was increased while increasing the pressure of sputtering chamber. On the other hand the porosity and grain size was decreased while decreasing the pressure of sputtering chamber. It shows that control of morphology and catalytic activity can be managed by modification of sputtering conditions. In the past, a thin film YSZ was usually fabricated by sputtering of ceramic targets. We used the reactive sputtering by mixture of oxygen in the sputtering gas to fabricate YSZ film from Y/Zr metal alloy. Application of above listed nano fabrication technic, we fabricated thin film SOFCs using Ru-Ni-GDC anodes for direct hydrocarbon operation. It showed about 80mW/cm2 of peak power density and it was less than 10% of performance difference than that of hydrogen operation. If the Ru-Ni-GDC mixture is more uniform, higher performance is expected Last, we fabricated thin film single chamber SOFCs and measured electro chemical performances. By co-sputtering of Ru-GDC in 200W and 50W respectively, nano-dendritic structure was successfully fabricated and it showed superior catalytic activity and thermo mechanical stability. The cathodes were fabricated with sputter and pulsed laser deposition. To improve the electric conductivity of nano fabricated perovskite cathode, Au was used as a current collecting and surface modifying material. The Au-SSC co-sputtered cathode shows more than 13time bigger peak power density compared to the pure SSC. In case of cell using pulsed laser deposited LSCF as a cathode, it showed 560mW/cm2 of peak power density at 550oC under single chamber condition of Rmix=2.