Functional Materials Research Laboratory
Dr. Stephen W. Sophie, Lab Coordinator
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.
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.
Sintering Performance and Electrical Properties of YSZ Ceramics:
This study focuses on the evaluation of nickel oxide as an electrolyte dopant, given the proven performance and compatibility of NiO with YSZ, as well as the low cost and availability of NiO within the SOFC research and industrial community. The affects of low level NiO dopants in both 8YSZ and 3YSZ in nano/micro particulate was evaluated in regards to density and densification rates as a function of dopant concentration and temperature. In addition to sintering behavior, the most critical feature of YSZ is ionic conduction, which was characterized by impedance spectroscopy to evaluate the affect of the dopant relevant to grain boundary and bulk conduction.