| Energy and environment issues have become major challenges for the sustainable development. Solid oxide fuel cell (SOFC), which is electrochemical device that convert chemical energy to electrical energy directly、efficiently and friendly to environment, has received enormous attention. Recently, for the commercialization of SOFC, intermediate temperature solid oxide fuel cell (IT-SOFC) has been called, asking for reducing the working temperature from traditional high temperature1000℃to intermediate temperature500-800℃. However, the electrochemical performance of traditional cathode is strongly dropped with reducing temperature. Therefore, it is critical to develop new cathode materials suited for operation at intermediate temperature. With the purpose, the electrochemical performance of YBaCo2O5+δ cathode material was improved through doping other elements.A series of layered perovskite oxide Y1-xCaxBaCo2O5+δ were made by partially replacing of Y with Ca, using a citric acid-nitrates auto ignition method. The XRD results showed that Y1-xCaxBaCo2O5+δ were chemically compatible with the Ceo.8Smo.201.9(SDC) electrolyte. With increasing the amount of Ca, the conductivity of Y1-xCaxBaCo2O5+δ oxide increased first and then decreased. Among them, Yo.8Ca0.2BaCo205+δ (YCBC2) possessed the most high conductivity, which was about500S-cm-1at400℃. The area specific resistance (ASR) results showed that YCBC2had the minimum ASR, which was0.26Ω·cm at650℃. An anode-supported single cell of Ni-SDC|SDC|YCBC2with humidified hydrogen (about3%H2O) as fuel and static air as oxidant was tested. The maximum power density was351mW-cm-2at650℃with the open-circuit voltage (OCV) value of0.81V. Present results demonstrated that YCBC cathode material was a very promising cathode for IT-SOFC.Composite materials YCBC2-xSDC (x=10-50, wt%) were made by mixing the YCBC2with SDC at different weight ratio. The electrical conductivity measurement showed that the conductivity of the samples decreased with increasing the amount of SDC. High temperature thermal expansion DIL402C was used to investigate the thermal expansion, indicating that YCBC2-30SDC had the lowest thermal expansion coefficient13.3×10-6K-1, which was very close to the intermediate temperature electrolyte SDC (12.2×10-6K-1). The area specific resistance (ASR) results showed that YCBC2-30SDC had the minimum ASR as low as0.06Ω·cm2at650℃. The maximum power density of the single cell Ni-SDC|SDC|YCBC2-30SDC at650℃was as high as553mW-cm-2. It indicated that the composite material YCBC2-xSDC, especially the YCBC2-30SDC, was a very promising and commercializing cathode for IT-SOFC.Auto ignition method was employed for layered perovskite oxide Yo.8Ca0.2Bao.5Sro.5Co205+δ (YCBSC) by substituting partially Sr for Ba in YCBC2. Compared with YCBC2, the Sr doped sample had lower conductivity but still larger than100S-cm-1. The average thermal expansion coefficient (TEC) at the temperature range of30-1000℃was17.4×10-6K-1. The maximum power density of the anode supported single cell Ni-SDC|SDC|YCBSC at650℃was about394mW-cm-2. It revealed that YCBSC was a promising cathode with favorable electrochemical performance.Yo.8Cao.2BaCoFe05+δ (YCBCF)oxide was synthesized by displacing partially Co in YCBC2with Fe with auto ignition method. At the temperature range of30-1000℃, the average TEC of the synthesized YCBCF was15.6×10-6K"1, suggesting that it match well with intermediate temperature electrolyte. A single cell with configuration of Ni-SDC|SDC|YCBCF was fabricated and examined with humidified hydrogen (about3%H2O) as fuel and static ambient air as oxidant. The maximum power density of the tested cell was422mW-cm-2at650℃, with the interface resistance value of0.12Ω·cm2. Present studies implied that the YCBCF material had a potential application as a cathode for IT-SOFC. |
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