PNNL

Abstract

Over the past several years, advances in materials and fabrication techniques for planar SOFCs have allowed for a reduction in SOFC operating temperatures (e.g., 650-800ºC) [1]. Consequently, relatively inexpensive ferritic stainless steels that have good thermal expansion matching with the ceramic cells are now considered to be among the most promising candidate materials for the construction of interconnects in SOFC stacks. To function well in the stacks, the metallic interconnects must demonstrate: (i) Excellent stability over thousands of hours in a very challenging “dual” environment, as they are exposed simultaneously to a reducing atmosphere (fuel, such as hydrogen) on one side and an oxidizing atmosphere (air) on the other side; (ii) High electrical conductivity through both the bulk material and in-situ formed oxide scales; (iii) Bulk and interfacial thermal mechanical reliability and durability at the operating temperature; (iv) Compatibility with other materials in contact with interconnects such as seals and electrical contact materials. Our screening work [2-4] has indicated that only few, if any, traditional compositions could completely satisfy the aforementioned materials requirements in the long term. This paper summarizes the results of our evaluation of newly developed alloys and selected oxide-coated stainless steels. In addition, the anomalous oxidation of stainless steels under the dual environment is also briefly discussed.