Development of High Performance Cathode for Intermediate-Temperature Solid Oxide Fuel Cells via Impregnation

在中温(500-600oC)下运行的固体氧化物燃料电池(SOFC)具有巨大的优势：(1)由于廉价的金属可用于互连、热交换器和结构部件，因此降低了SOFC系统的成本；(2)由于降低了运行温度，氧化、腐蚀、化学互扩散、热应力和蠕变变形将减少，因此提高了耐用性。然而，在较低的工作温度下，SOFC的电阻迅速增加，并且通常由电解液和阴极之间的阴极界面极化电阻主导。因此，通过开发新的正极材料和/或独特的微结构来降低界面极化电阻，可以显著降低SOFC的电阻。在不同的钙钛矿型SOFC正极材料中，钴酸盐具有最高的表面氧交换系数、氧化物离子电导率和中温电子电导。然而，钴铁矿在SOFC中作为阴极的功能是有限的，因为钴铁矿与其他电池组件相比具有更高的热膨胀系数，并且与最先进的YSZ(氧化钇稳定的氧化锆)电解液具有很高的化学反应活性。为了克服在高阴极制备温度下热膨胀失配和化学互扩散的障碍，PI利用浸渍沉积在多孔电解液骨架表面的钴催化剂复合材料开发了新的阴极结构。本项目的目的是论证采用浸渍法制备催化活性阴极的高离子导电多孔阴极架的可行性，研究阴极的微观结构特征与阴极电化学性能的相关性，比较电化学活性，了解合理设计更有效的阴极微结构，分析新型阴极结构的传输特性和限速步骤。本项目的智力优势是加深对新型阴极结构工作机理的基本理解，将新型阴极微结构的不同特征与阴极性能联系起来，确定纳米结构阴极催化剂上氧还原的传输特性和限速步骤，以优化阴极的微结构特征，评估新型阴极结构的长期耐久性，并应用新型阴极结构来提高固体氧化物燃料电池的低温性能和耐久性。更广泛的影响：新型阴极的使用有望在降低运行温度的情况下突破性地提高固体氧化物燃料电池的性能和耐用性。这将有助于这项技术迅速进入市场，以提高能源转换效率并大幅减少排放。通过积极推广这种新型的阴极结构，它将为科学界提供一种有效利用钴铁矿作为高性能阴极材料的技术。该项目还将通过让学生接触与材料科学相关的固体氧化物燃料电池研究，对南卡罗来纳大学的课程开发产生重大影响。强调代表不足的学生支持。突出了对高中生和普通公众的宣传，以促进对燃料电池技术的兴趣和认识。研究生和本科生的培训以及推广活动将有助于将固体氧化物燃料电池技术转移到美国产业，从而提高其全球竞争力。

0967166ChenSolid 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.