Enhancing the Redox Tolerance of Anode Supported Solid Oxide Fuel Cells by Microstructural Modification

Abstract

The most commonly used solid oxide fuel cell (SOFC) anode material is a two phase, nickel and yttria stabilized zirconia (Ni/YSZ) cermet. During fuel cell operation, this material is exposed to a reducing environment and thus remains a cermet. However, the metallic component of the anode may reoxidize in a commercial SOFC system due to situations such as seal leakage, fuel supply interruption or system shutdown. The reduction and oxidation of nickel will result in large bulk volume changes, which may have a significant effect on the integrity of interfaces within a fuel cell and thus result in performance degradation. Following an initial study of the redox kinetics and dimensional changes after reduction and oxidation, as well as a baseline characterization of the electrochemical performance degradation and microstructural changes after redox cycling, two modifications to the anode microstructure were made in order to enhance cell redox tolerance. The Ni content of the AFL was functionally graded in order to produce an AFL layer with minimal expansion during oxidation near the electrolyte and good electronic conductivity and thermal expansion match near the anode substrate. An oxidation barrier layer was printed on the bottom of the cell in order to restrict the ability of oxygen to flow into the anode. Both types of microstructural modification significantly improved the cell redox tolerance compared with standard baseline redox tests.