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Department of Mechanical and Industrial Engineering
Dr. Sofie received his Ph.D. in Materials Science & Engineering from the University of Washington in 2002. His area of expertise resides in innovative ceramic processing, materials synthesis and characterization, and device fabrication/testing, with extensive prior experience in functional oxide ceramic systems including high temperature YBCO superconductors for flywheel energy storage systems, compositional enhancement of PZT based high strain piezoceramics for medical ultrasound imaging. Dr. Sofie has developed several new ceramic processing approaches for customized device fabrication and microstructural control of pores and grain orientation/structures.
He joined the NASA Glenn Research Center solid oxide fuel cell team in 2003 working to develop novel sulfur tolerant anode materials, graded pore electrode structures, and advanced electrochemical testing systems to achieve robust, very high power density solid oxide fuel cells for aeronautics/aerospace applications. Dr. Sofie has recently co-developed a novel patent-pending SOFC concept to meet the demanding requirements of aerospace operation.
In 2005, Dr. Sofie joined the Mechanical Engineering faculty at Montana State University, continuing the development of high temperature electrochemical ceramics with research areas including SOFC anode development, novel planar SOFC concepts, fundamentals of sulfur tolerance, metal brazed seals, and engineered low tortuosity electrodes.
Electrode Development & Sulfur Tolerance: This activity focuses on the modification of traditional Ni/YSZ systems for anode supported technology with both electrochemically active and inert filler compounds to enhance anode performance while minimizing integration of new anode materials. The objective of the modified anode compositions is to improve durability by improving CTE match, thermal conductivity, and strength as well as achieving higher levels of sulfur tolerance. Further, fundamental studies are being performed to establish the mechanism of sulfur degradation in Ni/YSZ systems using high energy X-ray techniques which may lead to novel anode materials beyond the traditional system including all ceramic approaches.
Engineered Pore Structure & Gas Diffusion Characteristics: Research activities examining the effects of concentration polarization under high current densities suggest that gas diffusion through thick pore structures limits performance of SOFC’s. Typical electrode structures are fabricated with spherically shaped thermal fugitives (polymer & carbon powder additions). New techniques, based on tape casting technology, are being developed that are capable of generating ordered pore structures without the additions of thermal fugitives. A new tape casting technology (Freeze Tape Casting) is being developed by which a traditional cast tape is solidified uni-directionally solidified through the thickness of the tape. Through the precise control of slurry solids loading, freezing rate, and additives, engineered electrode structures can be fabricated to function as advanced solid oxide fuel cell electrodes that dramatically decrease tortuosity of the gas path. Further, studies are being performed on traditional and freeze tape cast anodes to understand the gas diffusion characteristics associated with concentration polarization.
Fuel cell design: While traditional anode supported cells (ASC) deliver high performance at relatively moderate temperatures, there are significant disadvantages to the design, including; shrinkage mismatch resulting in cell camber, CTE mismatch resulting in thermal stress, gas diffusion limitations, stack interconnection losses, and reactivity of electrode & electrolyte during sintering thus limiting the selection of potential electrode materials. A new design is being developed that will maintain a balanced symmetry for robustness and utilizing an interleaved micro-textured electrolyte support architecture that more than doubles active cell area while maintaining thin ionic conducting pathways for low area specific resistance (ASR). This new cell concept, developed as the Uni-Cell, is a merging of ASC and electrolyte supported cell (ESC) technology to maximize cell durability and to improve methods for sealing. The intended result is a cell that can be processed with the ease of electrolyte supported technology with low camber and robust mechanical properties. Electrode infiltration will also be utilized to further enhance the properties of this new concept.
Metallic Brazed Seals: While traditional approaches to SOFC sealing has been focused on compliant and/or rigid glass or glass/ceramic seals, the metallic braze seals may yield a more robust, mechanically stronger, and true hermetic seal. While significant challenges include the elimination of noble metals, shutting off electrical conductivity to prevent shorting of the cells, oxidiation resistance, metal/ceramic bonding, and thermal expansion mismatch, recent research in metallic braze seals shows promise to yield a viable and cost effective approach to SOFC sealing. A copper based braze system is being developed at MSU that forms a chemical and hermetic bond to metal and YSZ components and under the right treatment allows the shutdown of electronic conductivity to negate cell shorting issues. Fillers are also used in this system to control thermal expansion of the metal braze.
Web link: http://www.coe.montana.edu/me/faculty/sofie/research/