LSM Protective Coatings on Stainless Steel as Interconnects for Solid Oxide Fuel Cells
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LSM Protective Coatings on Stainless Steel as Interconnects for Solid Oxide Fuel Cells Ryan Eriksen1, Srikanth Gopalan1, Sanjay Sampath2, Yikai Chen2 1. Material Science Division, Boston University, Brookline, MA 02445, U.S.A. 2. Material Science and Engineering, Stony Brook University, Stony Brook, NY, U.S.A. ABSTRACT One of the major barriers to the adoption of solid oxide fuel cells (SOFCs) is the short lifetime of the fuel cell stacks. A stack consists of a number of cells in series separated by an interconnect. Due to the high temperatures necessary for SOFCs, typical commercial interconnects are ceramic. Great attention has been paid to decreasing the operating temperature of SOFCs in order to extend the life and decrease the cost of the stack. As operating temperatures decrease below 1000˚C, alternative interconnect materials become viable. Stainless steel interconnects are more cost effective than ceramic interconnects but the high temperatures and the oxidizing environment of the cathode leads to the formation of a chromium oxide scale that increases the stack resistance. Chromium from the stainless steel can also enter the vapor phase and redeposit on the cathode thereby blocking the electrochemically active sites. One method to neutralize these effects is to coat the metallic interconnect in a ceramic such as La.8Sr.2MnO3 (LSM). The coating acts as a diffusion barrier both against chromium diffusing into the cathode and oxygen diffusing into the interconnect. In this study LSM has been deposited using plasma spray and tested in a dual atmosphere setup using impedance spectroscopy to analyze the performance of the coatings at various temperatures. The area specific resistance and chemical composition of the scale was examined in order to determine the affect of the LSM coating. INTRODUCTION Solid oxide fuel cells (SOFCs) can utilize a wide variety of hydrocarbon fuels, making SOFCs a very attractive form of electricity production. The added benefit of easy modularization and high efficiencies gives SOFCs great potential while providing an alternative to burning fossil fuels. However technical challenges remain to SOFCs adoptability. In order to be economical an SOFC must have an operational lifetime of between 40,000 and 80,000 hours. Current SOFC stacks last on the order of 20,000 hours [2]–[6]. The cells in the SOFC are placed in series form a stack for practical applications. Each cell is then separated by an interconnect which functions as both an electrical connection between one cell to the next and a gas separator to prevent the fuel and oxidant from mixing. The interconnect must therefore be electrically conductive with low area specific resistance (ASR), impermeable to gases, stable under both oxidizing and reducing conditions, and mechanically durable to counteract for differences in the coefficient of thermal expansion (CTE). Interconnects also typically have channels that traverse the length of the fuel cell to allow rapid fuel and oxidant delivery across the cell, and therefore the interconnec
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