One of the key issues hindering the commercial success of solid oxide fuel cells (SOFCs) is their long term mechanical reliability. While significant progress has been made in the electrode materials development, cell and stack manufacturing technologies, as well as large-scale system level assemblies, the operating thermal gradients in the cell or stack still remains a challenge. The thermal gradients combined with mechanical loading can lead to glass seal or other ceramic component (anode, electrolyte, and cathode) failure in SOFCs. Apart from these components that can affect the stack reliability, another weakest link identified in the assembled planar stacks is the contact between electrodes and interconnects, especially on the cathode side. While these contacts not only provide the needed mechanical support for electrodes, they also provide the necessary electrical current path in the SOFC and their failure typically results in significant loss of performance. Hence, the electrode-interconnect contact strength and bond reliability is one of the key aspects of SOFC stack mechanical reliability. One way to ensure the reliability of cathode contact materials is by experiments; however, such experiments are expensive and may not be feasible for large stacks using current generation planar SOFCs. An alternative to experiments is computational modeling of contact material mechanics and bond reliability assessment based on available experimental data. The latter method though may not quantify reliability as accurately as design-specific experiments; it does provide significant insights on the contact mechanics and parameters affecting contact reliability of planar SOFCs in general.

This paper presents recent efforts on SOFC cathode contact modeling and reliability evaluations. For this work a continuum viscous sintering model was incorporated into a commercial FEA code to simulate contact paste sintering and evaluate the cathode contact reliability. The data required for the model implementation and contact reliability assessments were obtained from literature as well as experiments conducted in-house. Sensitivity studies were conducted to assess the influence of contact sintering parameters such as contact material thickness, sintering temperature, sintering pressure etc. using a generic planar SOFC design. The reliability evaluations of SOFCs were conducted at operating as well as shutdown states using commercial software based on Weibull statistics. The realistic operating temperatures of the generic stack were obtained from the in-house multi-physics code SOFC-MP. The sintering parameter sensitivity studies indicated that of all the parameters, sintering temperature has the most significant influence on the contact densification and associated stresses. The reliability evaluations indicated that cathode contact materials still require improved sintering and higher strengths to avoid failure under shutdown conditions.