Metal-Supported Solid Oxide Fuel Cell with High Power Density

Abstract

Metal-supported solid oxide fuel cells (mSOFC) 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 mSOFCs 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 mSOFCs 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 mSOFC 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 mSOFC. In this work, we seek to maximize mSOFC power density. This work is an extension of our previous efforts focusing on co-sintered, YSZ-based mSOFCs 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 mSOFCs 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 mSOFCs to date. Cell stability in the operating temperature range 600 to 750°C will also be presented. Acknowledgements Funding for this work was provided by Nissan Motor Co., Ltd. This work was funded in part by the U.S. Department of Energy under contract no. DE-AC02-05CH11231. Figure 1