Solid oxide fuel cells (SOFCs) operating at intermediate temperatures (500-600oC) could have tremendous advantages: (1) reduced cost of the SOFC systems since inexpensive metals can be used for interconnects, heat exchangers, and structural components and (2) improved durability since oxidation, corrosion, chemical interdiffusion, thermal stress and creep deformation will be reduced at reduced operating temperatures. However, at reduced operating temperatures, SOFC resistance increases rapidly and is often dominated by the cathode interfacial polarization resistance between the electrolyte and the cathode. Accordingly, the SOFC resistance could be substantially reduced by developing novel cathode materials and/or unique microstructures to lower the interfacial polarization resistance.
Among the different perovskite-type cathode materials for SOFCs, cobaltite has the highest surface oxygen exchange coefficient, oxide ion conductivity as well as electronic conductivity at intermediate temperatures. However, the functionality of cobaltite as a cathode in SOFC is limited since cobaltite has a much higher thermal expansion coefficient compared with the other cell components and has high chemical reactivity with the state-of-the-art YSZ (yttria stabilized zirconia) electrolyte. In order to overcome the barriers of thermal expansion mismatch as well as chemical interdiffusion at high cathode fabrication temperatures, novel cathode architectures have been developed by the PI, using a composite of the cobaltite catalyst deposited on the surface of the porous electrolyte frame through impregnation. The objectives of this project are to demonstrate the feasibility of the novel cathode architecture using a highly ionic conductive porous cathode frame coated with a catalytically active cathode via impregnation, to study the correlation of the microstructure features of the cathode with the cathode electrochemical performance, to compare the electrochemical activity and gain insight into rational design of more efficient cathode microstructure, and to analyze the transport properties and the rate-limiting step governing the novel cathode architecture.
Intellectual merits of the project are to develop a fundamental understanding of the working mechanism of the novel cathode architecture, to correlate the different features of the novel cathode microstructure with the cathode performance, to determine the transport properties and rate-limiting step for oxygen reduction on the nanostructured cathode catalyst in order to optimize the microstructure features of the cathode, to assess the long-term durability of the novel cathode architecture, and to apply the novel cathode structure to improve the performance and durability of the solid oxide fuel cells at reduced temperatures.
Broader Impacts: Utilization of the novel cathode is expected to bring breakthrough enhancement of the performance and durability of the solid oxide fuel cells at reduced operating temperatures. This will contribute to the rapid transition of this technology into the marketplace to improve energy conversion efficiency and greatly reduce emissions. By active dissemination of the novel cathode architecture, it will offer the scientific community a technique to effectively utilize cobaltite as a high performing cathode material. This project will also have a significant impact on the curriculum development at the University of South Carolina by exposing students to materials science-related solid oxide fuel cell research. Underrepresented student support is emphasized. Outreach to high school students and the general public to promote interest and awareness of the fuel cell technology is highlighted. The training of the graduate and undergraduate students and the outreach activities will help transfer the solid oxide fuel cell technology to US industry, thus enhancing its global competitiveness.
. Solid oxide fuel cells (SOFCs) offer many potential advantages for the conversion of renewable, carbon-based biofuels to electrical power, most notably the opportunity to provide fuel-flexible power systems without the need of noble metals for a variety of applications ranging from small scale to large scale. Furthermore, SOFCs offer high efficiency and low emissions. SOFCs operating at reduced temperatures (400-600 Celsius) are particularly important due to enhanced reliability and potential reduction of operating cost, but the overall fuel cell performance is typically limited by the sluggish oxygen reduction process in the cathode at these temperatures. The cathode performance is directly related to the cathode composition and microstructures. Outcomes of the intellectual merits of this award include discovery of new cathode compositions that enhance cathode catalytic activity, development of new fabrication methods that control and create unique cathode microstructures to facilitate mass and charge transport, and achieving fundamental understanding of the correlation of the novel cathode composition and microstructure with cathode performance. These research findings are extremely valuable to advance next generation solid oxide fuel cell technology for clean and sustainable energy supply. Outcomes of the broad impact of this project include generating fundamental knowledge of materials composition, structure, property relationship that can guide development of clean and sustainable energy technologies, producing multiple peer-reviewed publications based on the results from this award, presenting at national and international conferences of the research findings, training both graduate and undergraduate students in materials science and energy conversion and storage, offering one-week summer camp in nanotechnology and fuel cells to high school students, and outreaching to K-12 students and the general public to promote the interest and awareness of the fuel cell and other related clean energy technology.
