PNNL

Abstract

Currently, acceptor-doped lanthanum chromite is the state-of-the-art ceramic interconnect material for high temperature solid oxide fuel cells (SOFCs) due to its fairly good electronic conductivity and chemical stability in both oxidizing and reducing atmospheres, and thermal compatibility with other cell components. The major challenge for acceptor-doped lanthanum chromite for SOFC interconnect applications is its inferior sintering behavior in air, which has been attributed to the development of a thin layer of Cr2O3 at the interparticle necks during the initial stages of sintering. In addition, lanthanum chromite is reactive with YSZ electrolyte at high temperatures, forming a highly resistive lanthanum zirconate phase (La2Zr2O7), which further complicates co-firing processes. Acceptor-doped yttrium chromite is considered to be one of the promising alternatives to acceptor-doped lanthanum chromite because it is more stable with respect to the formation of hydroxides in SOFC operating conditions, and the formation of impurity phases can be effectively avoided at co-firing temperatures. In addition, calcium-doped yttrium chromite exhibits higher mechanical strength than lanthanum chromite-based materials. The major drawback of yttrium chromite is considered to be its lower electrical conductivity than lanthanum chromite. The properties of yttrium chromites could possibly be improved and optimized by partial substitution of chromium with various transition metals. During FY10, PNNL investigated the effect of various transition metal doping on chemical stability, sintering and thermal expansion behavior, microstructure, electronic and ionic conductivity, and chemical compatibility with other cell components to develop the optimized ceramic interconnect material.