Novel High-Performance Electrodes for Medium-Temperature Solid Oxide Fuel Cells

固体氧化物燃料电池（sofc）有望在各种类型的燃料电池中提供最高的能量转换效率。目前，由于最先进的电解质和电极在低温下的性能不足，SOFC的工作温度限制在1000℃左右的非常高的值。然而，理想的是在中温（-800℃）下操作SOFC，因为高温操作会导致许多严重的问题：SOFC组件的降解，材料的选择有限等。运行中温sofc必须解决两个主要障碍。首先是减少固体电解质中的欧姆损耗。除了降低欧姆损耗外，开发高性能电极也至关重要，因为在这样的温度下，电极的反应速率必须减慢。我们开发了一种用于中温SOFCs的多孔催化反应层。混合导电氧化物粒子，钐掺杂的铈[(CeO_2)_<0.8>(SmO_<1.5…More >)_<0.2>，标记为SDC]为阳极，La(Sr)MnO_3 （LSM）为阴极，与表面高度分散（纳米尺寸）的金属电催化剂结合使用。本研究的目的是通过制造高性能、高可靠性的新型电极，为高性能中温SOFC的发展做出贡献。1999财年，我们成功开发出高性能的新型阴极。La(Sr)CoO_3 （LSC）具有比LSM更高的阴极性能。然而，在高温下，LSC比LSM更容易与钇稳定的氧化锆（YSZ）电解质反应。我们发现薄而致密的SDC中间层可以有效地避免LSC和YSZ之间的不良固相反应。在不增加欧姆电阻的情况下，控制LSC阴极的微观结构可以明显降低无红外过电位。在低工作温度下，负载为3wt %的高分散Pt催化剂进一步提高了阴极性能。在800℃空气中，过电位（η）为-0.05 V时，Pt-LSC阴极上的电流密度为1 A/cm^2。在2000财年，我们成功地通过使用掺钇铈（YDC）代替SDC来提高阳极性能。我们发现在800 ~ 1000℃的工作温度下，多孔YDC阳极比SDC阳极表现出更高的性能。混合导电YDC的高电子导电性显著提高了阳极反应速率。高度分散的Ru催化剂（3wt %）有效地提高了YDC阳极的性能。在800℃的湿化H_2条件下，η= 0.1 V时的电流密度可达0.4 A/cm^2。总之，它们是中温sofc的理想电极。少

Solid oxide fuel cells (SOFCs) are expected to provide the highest energy conversion efficiency among various types of fuel cells. At present, the SOFC operating temperatures are restricted to very high values of about 1000℃ because of insufficient performances of the state-of-the-art electrolyte and electrodes at low temperatures. It is desirable, however, to operate SOFCs at a medium temperature (-800℃) because high-temperature operation causes many serious problems : degradation of SOFC components, limited choice of materials, etc. Two major obstacles must be solved to operate mediunm-temperature SOFCs. The first is to reduce an ohmic loss in the solid electrolyte. Besides reducing the ohmic loss, it is essential to develop high performance electrodes because the electrode reaction rates must be slow down at such temperatures.We have developed a porous catalyzed-reaction layer for medium-temperature SOFCs. Mixed conducting oxide particles, samaria-doped ceria [(CeO_2)_<0.8>(SmO_<1.5 … More >)_<0.2>, denoted as SDC] for the anode and La(Sr)MnO_3 (LSM) for the cathode, were employed in combination with highly dispersed (nanometer-sized) metal electrocatalysts on their surfaces.The aim of this research work is to contribute to development of high-performance medium-temperature SOFC by fabricating novel electrodes with high performance and high reliability.In FY1999, we succeeded to develop new cathodes with exceptionally high-performance. La(Sr)CoO_3 (LSC) has been known to exhibit a higher cathodic performance than LSM.However, LSC tends to react easier with yttria-stabilized zirconia (YSZ) electrolyte than LSM at high temperatures. We found that a thin and dense SDC interlayer was effective to avoid unfavorable solid-state reactions between LSC and YSZ.Control of the microstructure of LSC cathode appreciably lowered the IR-free overpotential without an increase of the ohmic resistance. The cathode performance was enhanced further with highly dispersed Pt catalysts of 3 wt% loading, especially at low operating temperature. The current density on the Pt-LSC cathode at an overpotential (η) of -0.05 V was 1 A/cm^2 at 800℃ in air.In FY2000, we succeeded to enhance the anode performance by employing yttria-doped ceria (YDC) in place of SDC.We found that the porous YDC anode exhibited higher performance than that of SDC at the operating temperature of 800℃ to 1000℃. High electronic conductivity in the mixed conducting YDC appreciably contributes to enhancing the anode reaction rate. Highly dispersed Ru catalysts (3 wt%) effectively enhanced the performance of the YDC anode. The current density of 0.4 A/cm^2 at η= 0.1 V was achieved at 800℃ in humidified H_2. In conclusion, they are promising electrodes for medium-temperature SOFCs. Less