Development of a novel high performance electrolyte supported solid oxide fuel cell
Gentile, Paul Steven.
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High power solid oxide fuel cell (SOFC) stacks are based on the planar design concept to yield high specific power densities. The key engineering challenges to planar stack reliability and robust operation is attaining low resistance interconnection of individual cells in series and hermetic sealing of interconnects. While stack design and contact paste development is paramount to address this issue, the basic design of the fuel cell introduces limitations. State-of-the-art anode supported cells (ASC) yield high power densities due to low ASR thin electrolytes, however, the asymmetrical design, anode/electrolyte CTE mismatch, and thick support anode yields undesirable cell camber and fuel transport issues. These deficiencies lead to poor interconnect contact, non-optimal sealing surfaces, and poor fuel utilization, which can mitigate the key benefit of the ASC. Conversely, the electrolyte supported cell (ESC) presents a host of advantages from ease of processing, large diameter scale-up potential, mechanical robustness, optimal seal contact surface, thin electrodes, and minimal cell curvature with the key obstacle arising from high cell ASR due to the thick structural electrolyte. MSU has developed a novel cell concept that merges the benefits of the ASC and ESC designs.The "UniCell" concept has been designed to effectively lower the ASR of thick electrolyte supports while maintaining the traditional advantages of the ESC technology utilizing innovative, post ceramic processed, engineering techniques. SOFC fabrication methods of the electrolyte substrate established on xylene/ethanol solvent based yttria stabilized zirconia (YSZ) slurry include thin film tape casting and high temperature sintering. Photo-resist machining and laser drilling of interleaved electrolyte texture introduced into both surfaces of the YSZ green tapes and sintered substrates have been investigated. The findings of a dispersion study, thermo gravitational analysis performed to minimize microstructure defects due to rapid organic burnout, dilatometer investigation of sintering shrinkage and FEM microstructure analysis of electrolytes will be discussed. Mechanical strength testing via concentric ring on ring tests, and fuel cell performance data will be reported and compared to an ESC baseline to establish the feasibility of this concept. Alternative methods explored to introduce features during ceramic processing to reduce the process cost will be reviewed.