High Efficiency CFY-Stack for High Power Applications

Abstract

SOFC modules with a power of 5 to 50 kW are a serious competitor to commercially available combined heat and power plants for decentralized electricity and heat supply with high electrical efficiency. Electrical efficiency and electrical power of a SOFC stack are essential for its profitable operation. The highest power density and electrical efficiency can only be achieved with planar SOFC stacks. Electrolyte supported cells with 10ScSZ electrolytes allow power densities of more than 500 mW/cm². On account of the thermomechanical properties of electrolyte, this potential can only be used in stacks with chromium based interconnects (CFY from Plansee SE). High power, robustness and long-term stability are essential for stationary SOFC systems. In order to fulfill these requirements, Fraunhofer IKTS in close collaboration with Plansee SE develops a new stack design with larger active area, simple cathode contacting, external cathode manifold and optimized interconnect layer. This paper will give an overview of the current SOFC stack development focused on power output, long-term stability, temperature cycling and reliability of SOFC stack assembling. Material Combination for SOFC Stacks with High EfficiencyPlanar Solid Oxide Fuel Cells (SOFC) are considered to be highly efficient power generators with low emission levels even for small power units (1-200 kW el ). The recently developed and up-scaled net-shape technology for powder metallurgical production of bipolar plates allows new options for application of electrolyte supported cells with area specific resistances (ASR) <0.3 Ωcm² and are a match to stacks with anode supported cells (1-4). The electrolyte supported cells have benefits in long-term stability and thermal cyclability which were previously tested and are important parameter for a robust SOFC-system.The development of SOFC stacks with interconnects made from powder metallurgical processed chromium-iron-yttria based alloy (CFY) and scandia stabilized zirconia electrolytes (10ScSZ) have a long history and have surpassed the line to mass production in recent years.The bipolar plates of the new stack design (MK35x) have dimensions of 130x150x3.2 mm³. Currently, it is the biggest CFY interconnect and has a good ratio of active area to ECS Transactions, 35 (1) 269-277 (2011) 10.1149/1.3570002 © The Electrochemical Society 269 ) unless CC License in place (see abstract). ecsdl.org/site/terms_use address. Redistribution subject to ECS terms of use (see 160.39.73.191 Downloaded on 2015-03-24 to IP

Long Term Performance of Stacks with Chromium-Based Interconnects (CFY)

“…Until 2012 MK351 stacks were built with a state of art protective coating at that time and it was applied manually. As reported recently, (15) stacks was in the range of 1.5-1.7 %/1,000h. After the optimization of composition of protection layers and introduction of a semi-automatic coating process Plansee / IKTS succeeded to reduce the degradation rate of the MK351 stack significantly.…”

Analysis of the Cathode Electrical Contact in SOFC Stacks

“…R Others include other components of the ohmic resistance, such as the oxidation of the metallic interconnector, and are assumed to be minor with regard to the electrolyte and cathode contact shares. 34,35 So the cathode contact resistance is being isolated by using multiple stacks (see Table I) with structural differences. The resistance of the cathode contact for different temperatures is presented in Figure 5.…”

Glass ceramics sealants for SOFC interconnects based on a high chromium sinter alloy

“…A second stack were tested under constant electrolysis operation at I = −35 A with an average cell voltage of Ucell = 1.3 V for a duration of more than 3000 hours at T = 800°C. Details on the background of the testing procedures and results are described by Megel et al It is important to mention that the stacks remained intact after these test runs without any cracks in the sealant, the CFY interconnectors or the ceramic electrolytes which in turn would accelerate degradation of the stacks or cause direct combustion and overheating. After successful implementation of the testing procedures, the stacks were cooled down and the so called “post mortem analysis” was conducted.…”

“…Additionally, an optimized sealing glass (denoted as FS‐p) was tested in CFY‐based SOFC stacks. Details of the used SOFC stack type and testing procedures of such stacks are described in previous publications . Figure depicts an explosion view of a part CFY‐based SOFC stack, including all relevant components which are necessary to assemble a fully functional stack.…”