(Invited) Metal-Supported Solid Oxide Fuel Cells with High Power Density

Abstract

Metal-supported solid oxide fuel cells (MS-SOFC) display a number of advantages over conventional all-ceramic SOFCs, including low-cost structural materials (e.g. stainless steel), mechanical ruggedness, excellent tolerance to redox cycling, and extremely fast start-up capability. Challenges for MS-SOFCs include: oxidation of the metal support, especially at 800°C and above; the possibility of the stainless steel exacerbating Cr poisoning of the cathode catalyst; fabrication and materials set restrictions arising from the requirement that stainless steel be sintered in reducing atmosphere; and, only moderate performance and lifetime have been demonstrated to date. These advantages and challenges suggest that MS-SOFCs may be well-suited for portable, ruggedized, fast-start, intermittent-fuel, or other unique and innovative applications. Nissan has developed the world’s first light-duty vehicle with a conventional SOFC stack for traction power, fueled by bio-ethanol reformate. Because of the desire for rapid-start capability, developing MS-SOFC cell and stack technology for this vehicular application is a priority. The small volume allowance for the SOFC stack on-board a small vehicle furthermore demands high power density from the MS-SOFC. In this work, we seek to maximize MS-SOFC power density. This work is an extension of our previous efforts focusing on co-sintered, YSZ-based MS-SOFCs with porous metal supports on both anode and cathode sides, with catalysts deposited into both electrodes via infiltration. These features provide for a mechanically rugged cell that can be processed with low-cost scalable techniques, and high surface-area catalysts that provide excellent performance by avoiding interdiffusion or coarsening during cell sintering. To support the vehicular traction application, in this work we further develop catalyst infiltration processing for MS-SOFCs to dramatically increase power density. The goal is to increase cell performance by improving infiltration of conventional catalyst compositions (lanthanum strontium manganite (LSM), Ni, doped ceria) into electrode backbones of conventional yttria-stabilized zirconia (YSZ). Various aspects of the infiltration procedure were optimized, including: precursor composition and dilution with water; catalyst loading; and, crystallization temperature. Figure 1 shows the resulting high performance. Peak power of 1.1 and 1.9 W/cm2 is achieved at 700°C and 800°C, respectively, and the 800°C performance is the highest reported for stainless steel-supported MS-SOFCs to date. Figure 2 shows initial stability of the MS-SOFC. Testing is ongoing, and operation for >1000 h and post-mortem analysis will also be presented. Demonstration of redox cycling and rapid-start tolerance will be discussed. Acknowledgements Funding for this work was provided by Nissan Motor Co., Ltd. through Strategic Partnership Projects Agreement FP00004436. This work was funded in part by the U.S. Department of Energy under contract no. DE-AC02-05CH11231. Figure 1