Flatness Enhancement of Metal-Supported Solid Oxide Fuel Cells with Additional Compensation Layer

Abstract

Solid oxide fuel cells are high-temperature fuel cells which offer several advantages: high efficiency, fuel flexibility, high-quality waste heat, and the use of non-noble metal catalysts. Metal-supported solid oxide fuel cells, in which the ceramic mechanical support layer is replaced with the metal support, are considered as next-generation solid oxide fuel cells because of their enhanced mechanical/thermal ruggedness compared to conventional ceramic-supported solid oxide fuel cells. However, different thermomechanical behavior of metal support and ceramic layers during sintering makes metal-supported cells vulnerable to warping. Cell warpage must be minimized because it reduces not only uniformity of wet-chemical coating, but also actual contact area between electrode and interconnect, increasing the contact resistance.In this study, causes of metal-supported cell warpage are identified, and the design that can minimize cell warpage is suggested for successful scale-up of metal-supported solid oxide fuel cells. Through thermomechanical and residual stress analyses, it is found that residual stress derived from coefficient of thermal expansion mismatch between electrode layers and the metal substrate is the main cause of the warpage of metal-supported solid oxide fuel cells. Based on these results, a novel design that has thicker metal protection layer on the opposite side of the electrolyte is proposed for minimizing cell warpage due to residual stress. Through the design modification, vertical deformation of 2-inch metal-supported solid oxide fuel cell can be successfully controlled to 17.36% of the previous design. Furthermore, electrochemical evaluation showed a 21% decrease in ohmic ASR and a 25% increase in peak power density after the design modification, implicating reduction of contact resistance as a result of increased contact area by enhanced flatness.