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，由于现有电解质和电极在低温下的性能不足，SOFC的工作温度被限制在约1000℃的非常高的值。然而，希望在中温（-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。第一是减少固体电解质中的欧姆损失。除了降低欧姆损失外，由于在中温SOFC中电极反应速率必须降低，因此开发高性能电极也是必要的。钐掺杂氧化铈[（CeO_2）_<0.8>（SmO_&lt;1.5 关于我们 （<0.2>SDC）_（表示为SDC]）和La（Sr）MnO_3（LSM）（表示为阴极）与高度分散的（纳米尺寸）金属电催化剂。本研究工作的目的是通过制造具有高性能和高可靠性的新型电极，为开发高性能中温SOFC做出贡献。我们成功地开发出了具有极高性能的新阴极。La（Sr）CoO_3（LSC）具有比LSM更好的阴极性能，但在高温下，LSC比LSM更容易与YSZ电解液反应。我们发现，一个薄而致密的SDC中间层是有效的，以避免LSC和YSZ之间的不利的固态反应。LSC阴极的微观结构的控制显着降低IR自由过电位，而不增加欧姆电阻。阴极性能进一步增强与高度分散的Pt催化剂的负载量为3重量%，特别是在低操作温度。在800℃空气中，Pt-LSC阴极在过电位（η）为-0.05 V时的电流密度为1 A/cm^2。在FY 2000中，我们成功地用氧化钇掺杂的氧化铈（YDC）代替SDC来提高阳极性能，发现在800 ~ 1000℃的工作温度下，多孔YDC阳极的性能优于SDC。混合导电YDC中的高电子电导率明显有助于提高阳极反应速率。高度分散的Ru催化剂（3wt%）有效地增强了YDC阳极的性能。在800℃、湿H_2气氛中，在η= 0.1V时，电流密度为0.4A/cm ~ 2。总之，它们是中温SOFC的有前途的电极。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