Initial Testing of Solutions to Redox Problems with Anode-Supported SOFC

The most commonly used solid oxide fuel cell (SOFC) anode material is a two phase nickel- and yttria-stabilized zirconia (Ni/YSZ) cermet. During typical fuel cell operation, this material remains a cermet; however, in a commercial SOFC system seal leakage, fuel supply interruption, or other situations may cause the anode to reoxidize. The cyclic reduction and oxidation (redox) of nickel results in large bulk volume changes, which may have a significant effect on the integrity of interfaces within the fuel cell and thus may cause significant performance degradation. Following initial study of the degradation mechanisms and redox kinetics, a number of solutions have been devised. These can be broadly categorized into system solutions and unit cell or materials solutions. The former includes purge gas, other means to produce a reducing gas, cell reversal, and passive solutions such as hydrides, oxygen getters, and steam purging. The latter includes alternative anode materials, microstructural modification of anode functional layers (AFLs), graded porosity, and composition of AFL and redox barrier layers. This paper discusses the pros and cons of each approach and some initial feasibility testing in short-stack repeat units.