Medium Temperature Operating Solid Oxide Fuel Cells Using Hydrocarbon Fuels

点击翻译按钮获取中文摘要

Solid oxide fuel cells (SOFCs) are expected to provide high energy conversion efficiencies. The SOFCs have a potential of use of hydrocarbon fuels, which can be reformed internally to reactive fuels such as hydrogen or carbon monoxide on the anode. It is desirable to operate SOFCs at a medium temperature (700〜800℃) to overcome problems such as degradation of the construction materials, sintering of electrodes, and a limited choice of materials. The aim of this research project is to develop high performance anodes for the internal reforming-type SOFCs operating at medium temperatures. We obtained the following results.1.Mixed conducting samaria-doped ceria (SDC) anodes with a small amount of Ni nanoparticles (8 vol.%) exhibited a higher performance in SOFC operated at 700-900℃ than that of Ni-SDC cermet. Microstructural analyses of Ni-dispersed SDC showed that nanometer-sized Ni catalysts enhanced the anodic reaction rate by increasing the active reaction sites and lowering the electro … More nic resistance in the anode effectively. The Ni-dispersed SDC anode exhibited a stable performance at 800℃ and 0.6 A cm^<-2> in humidified H_2 for a long term over 1100 h. We succeeded to clarify a mechanism for the stabilization of the anode microstructure during the long term operation.2.The Ni-dispersed SDC anode could be operated with methane at S/C (steam to carbon ratio) of unity, which was lower than that required for complete steam reforming. It was found that CH_4 was reformed additionally by utilizing water vapor formed by the anode discharging reaction. The carbon deposition could be suppressed by increasing the amount of catalysts or changing the kind of catalyst dispersed on the SDC.3.We have found that the Ni (8 vol.%)-dispersed SDC was also applied to the cathode in solid oxide electrolysis cell (SOEC) for efficient production of hydrogen. An SOEC, comprised of Ni-dispersed SDC cathode, La(Sr)CoO_3 anode with SDC interlayer and YSZ electrolyte, exhibited fairly high performance ; IR-free cell voltage=1.20 V at 0.50 A cm^<-2> and 900℃ under the atmosphere of H_2+H2_O(p[H_2]=0.6 atm, p[H2_O]=0.4 atm) and O_2 (1 atm). Less