PNNL

Abstract

The identification and fabrication of suitable interconnect materials is a major challenge in the development of SOFCs [1,2]. The primary function of the interconnect is to carry electrical current from the electrochemical cell to the external circuit, so the inteconnect material must have good electrical conductivity. In addition, the interconnect must be chemically and mechanically stable for operation at high temperatures for long periods of time. This is especially challenging, since the interconnect is exposed to both oxidizing conditions at the cathode and reducing conditions at the anode. Thus, interconnect materials should not undergo significant dimensional changes with changes in either temperature or oxygen partial pressure. One such change is thermal expansion, which must be matched with the expansion of other fuel cell components to avoid the generation of thermal stresses during heating or cooling. Similarly, some materials undergo expansion or contraction with changes in oxygen partial pressure, which can also lead to stresses in the fuel cell. Thus, although the interconnect is not always a load-bearing component, moderate mechanical strength of the interconnect material is required to avoid fracture when stresses are generated during operation. Even higher strength is required in some planar designs were the interconnect provides structural support. In such designs, the interconnect also separates the fuel from air, so oxygen and hydrogen permeability should be low. The interconnect material must also be chemically stable with other fuel cell components. This includes not only stability during fuel cell operation, but also during fabrication, which typically involves higher temperatures. Finally, ease of fabrication and cost are important so that application of the fuel cell is economically feasible.