Fabrication of Low-Profile and Large Size Solid Oxide Fuel Cell Combined with Strength Reinforcement Layer and Shrinkage Control Layer

摘要

The power output of a planar SOFC can be increased by enlarging the cell size and providing the fuel gas to the reaction site more effectively. For this reason, a SOFC tends to be larger in area and thinner in thickness. However, in a planar SOFC, larger area causes bigger camber in co-firing process due to larger shrinkage mismatch between layers such as the electrolyte, the anode function layer and the support. It is even more difficult for a large cell to achieve low cell thickness because reduction of cell thickness worsens the camber. Moreover, thinner cells show much lower mechanical strength in a ring-on-ring test, which means more problems in handling, stacking and operating in SOFC stacks. Last year we presented a fabrication route which enabled us to achieve large SOFCs with high performances. In this study, we demonstrate a new fabrication method to make large and thinner cells having small camber without undermining mechanical strength. The support of the cell consists of two types of layers with different functions. One is for reinforcing the mechanical strength and the other is for controlling the shrinkage rate in co-firing. For the designated functions, each layer is controlled by YSZ/NiO ratio, Y2O3 contents in YSZ and pore former amounts. All layers constituting electrolyte, anode function layer and support were fabricated by tape casting of wet slurry, and lamination by automated multilayer stacking machine. In the new structure, cells show very small camber and no decrease in mechanical strength even if cell dimensions were 0.7 mm in thickness and 704 cm2 in area. From the button cell test, the maximum power density of 0.7mm thickness cell was 11% higher than that of 1.1 mm thickness cell. Additionally, it was proved by the large size single cell test that the thinner cell was superior to the thicker one in high fuel utilization condition. Besides increasing power density and fuel utilization, thinner cells will be also advantageous for reducing the volume of SOFC stack and materials cost.