PNNL

Abstract

For SOFC stack designs which utilize higher operating temperatures, ceramic interconnects are required. Currently, acceptor-doped lanthanum chromite is the predominant ceramic interconnect material due to its relatively good stability, electrical conductivity, and thermal expansion match. However, it exhibits inferior sintering behavior, and is susceptible to hydration in moist environments. In addition, it undergoes a phase transition from orthorhombic to rhombohedral symmetry upon heating, and is reactive with YSZ electrolyte at high temperatures. Therefore, an alternate interconnect material is needed to overcome these technical limitations of acceptor-doped lanthanum chromite. Yttrium chromite-based perovskites exhibit several attractive features for interconnect applications over lanthanum chromites such as stability with respect to formation of hydroxides, low chemical expansion in reducing environments, and chemical compatibility with YSZ electrolyte. The electrical conductivity of yttrium chromite is known to be relatively low, but can be improved by multiple doping on A- and B-sites. Electrical and thermal properties of yttrium chromite are strongly influenced by transition metal doping on B-site, and the basic properties of yttrium chromite could possibly be refined and optimized by a wide variety of dopants to satisfy the rigorous requirements for SOFC interconnect applications. During FY 2011, PNNL investigated the effect of Co-, Ni-, and Cu-doping on thermal and electrical properties of yttrium chromite. Co-firing and constrained sintering behavior of doped yttrium chromite was evaluated, and densification of screen-printed layer was improved by the addition of infiltration steps. Based on the results, an optimized composition for SOFC interconnect application was proposed.