Towards robust co-fired metal- supported solid oxide fuel cell with alternative anodes

Abstract

Solid oxide fuel cells (SOFCs) are the highly efficient devices that directly convert chemicals into electricity with non-toxic byproducts such as water and carbon dioxide and have been operated conventionally at high temperature as 800~1000oC. Recently, by applying metal supports (MS) into the cell architecture (MS-SOFC) also using new alternative anodes, it is feasible to operate the cell at low temperature at 600 °C. Also, applying metals provide excellent thermal cycling ability while maintaining a strong interlayer bond. The objective of this dissertation is to introduce and to develop new materials for fabrication of very robust, high precision, and cost-effective manufacturing technique for MS-SOFCs. Finally, cells supported by stainless steel (STS) with alternative anodes are co-fired and evaluated at 550-700 °C. We, firstly, examined the firing and oxidation behavior of porous STS as a core part for fabrication of MS-SOFC. Then, for the first time in the world, we used alternative anodes (La,Ni co-doped in SrTiO3 or LSTN) in MS-SOFCs. This is the first successful use and fabrication of STS- supported cell with alternative anodes. Part I (Chapter 3) deals with assessing the effect of LSTN-coating on area specific resistance (ASR) of porous tape during exposure to wet H2. Chromia growth can lead to severe increase in ASR. Applying LSTN coating on open surface of porous STS pellet reduces chromia growth rate by preventing diffusion of Cr ions or O ions. Part II (Chapter 4), we quantified how Cr evaporation from porous STS affects anodic resistance, which has not been reported to the best of our knowledge. We quantify the effects of oxide formation and Cr evaporation of porous STS on RΩ and RP in the anode atmosphere. The aim of Part III (Chapter 5) is to demonstrate the feasibility of using LSTN mixed with YSZ as an alternative anode in MS-SOFC. According to our knowledge, MS-SOFC with LST-based anode has not been investigated. In this study, the cell fabrication and the electrochemical performance of the cell at 550-650 °C were investigated. Part IV (Chapter 6) includes the study for demonstrating the feasibility of fabricating MS-SOFC using a new design that uses STS as a support, and includes a new three-phase composite anode, LSTN-YSZ-Ni as an alternative to conventional anodes (Ni/Yttria-stabilized zirconia (YSZ) or Ni/Gadolinia-doped Ceria (GDC). LSTN-YSZ-NiO in 3:3:4 wt. ratio (LYN) was selected for the test.