Cost is a key factor constraining the commercialization of Solid Oxide Fuel Cell (SOFC) stacks. Improving the output power density of SOFC stacks has been considered an important way to reduce the cost effectively. It is usually the case that the output power density of the stack assembled by large-area cells is lower than that of single cells with small area. For example, the output power density of a single cell with an area of 4cmX4cm can reach 0.4Wcm-2 at 750℃, whereas the power density of a stack assembled with 10cmX10cm cells usually can only be 0.2 Wcm-2 at 750℃. Moreover, the output power density may decrease with the increasing number of cells in the stack.
In order to improve the output power density of SOFC stacks, the researchers from the Ningbo Institute of Material Technology & Engineering (NIMTE) has conducted extensive research on the contact between the cell and interconnect with the financial support of Ministry of Science and Technology of China and the Chinese Academy of Sciences. It was found that the depth of contacting between cathode and interconnect was the key factor influencing the output power density of SOFC stacks (Fuel Cells, 11, 445-450, 2011). A new contacting method, namely the Whole Soft-Contacting, was thus designed (Patent application number: PCT/CN2012/071851) to improve the interface contacting between cell cathode and metal interconnect in SOFC stacks.
Using this new contacting method, the NIMTE researchers assembled several stacks with 5-30 anode-supported cells. The figure below shows polarization curves for a 5-cell and a 30-cell stack. The 5-cell stack obtained an open circuit voltage (OCV) of 5.94V at 800℃ and a maximum power of 163.1W with the corresponding power density of 0.52Wcm-2. The fuel utilization was calculated to be 48%. For the 30-cell stack with a volume of 10cmX10cmX8.5cm, a maximum power of stack of 868.4W was achieved at 800℃, with an OCV of 35.2V. The maximum power density was 0.46Wcm-2, with a corresponding volume power density of 1 kW/L and a fuel utilization of 60.4%.