YST-CeO2 conposite as a diffusion barrier layer for metal-supported solid oxide fuel cell

Abstract

Metal-supported solid oxide fuel cells (MS-SOFCs) are promising due to their good mechanical strength, thermal cycling resistance and fast heating & cooling ability. These properties are suitable for the mobile and portable application. Stainless steel (STS) is a suitable metal support material because of its low cost and TEC(Thermal Expansion Coefficient) match with electrolyte material. However, metal-supported SOFC with Stainless steel has problems due to the diffusion of Ni in Ni-based anode and Fe, Cr in STS support during sintering and operation. The diffusion of Ni in the anode into the STS support changes the ferritic STS to the austenitic STS. This change further leads to the increase of TEC of STS, and then causes TEC mismatch between the support and the other components of cell. The diffusion of Fe and Cr in STS support to Ni-based anode also converts Ni particles in the anode into a Ni-based alloy. This change decreases the electrochemical activity of anode, and degrades the cell performance. In order to solve these problems, this study focused on a diffusion barrier layer (DBL) to avoid the reaction between the Ni-based anode and the ferritic STS support. One of the materials used for a diffusion barrier is CeO2. CeO2 has good function as the effective diffusion barriers. However CeO2 has a very poor mechanical property in reducing atmosphere. Since yttrium-doped strontium titanate (YST) has a better mechanical property and higher electrical conductivity than CeO2 in reducing atmosphere, YST or YST composite materials was tested in this study as a diffusion barrier. YST and CeO2 in 1:1 weight ratio were mixed to obtain the respective advantage of materials. Metal-supported cell was fabricated using YST-CeO2 composite as a diffusion barrier layer between the anode and the support at 1300oC for 3h in 5%H2-95%Ar. YST-CeO2 composite layer was mechanically stable and was porous in reducing atmosphere. YST-CeO2 composite layer also satisfactorily prevented the inter-diffusion of Ni, Fe and Cr. The single cell showed the OCV value of 1.1V and a maximum power density of ~ 42mW/cm2 at 700oC.In this study, we were studied a diffusion barrier layer to avoid reaction between the anode and the support. YST-CeO2 was mechanically stable in reducing atmosphere and thus an effective diffusion barrier. Therefore, YST-CeO2 is a promising candidate for use in the metal-supported SOFC.