| K2NiF4-type layered perovskite oxides generally exhibit excellent oxygen ion surface exchange kinetics and fast bulk transfer properties.Moreover,their thermal expansion coefficients(13.0×10-6K-1)are well matched with commonly used electrolytes in solid Oxide fuel cell?SOFC?.So they are potential candidates as electrodes for SOFC.K2NiF4-type oxides such as Ln2NiO4?Ln=La,Pr,Nb?,La2CuO4 have been extensively studied as cathode materials for SOFC;however,they are not suitable for anode due to their instability under reducing atmosphere.Up to now,the K2NiF4-type redox stable anode materials has been only reported for La0.6Sr1.4MnO4,nevertheless,the anode suffers from insufficient electrochemical activity for oxidation of fuels with maximum output power density(Pmax)of 153mW cm-2 at 850?in a SDC electrolyte single cell with wet H2 as fuel.In this thesis,SrLaFeO4?LSF?and SrPrFeO4?PSF?were prepared by solid-state reaction method,and their physical and chemical properties have been investigated,such as crystal structure,thermal expansion coefficient,conductivity,electrochemical catalytic properties and stability.The SOFCs with LSF or PSF as anodes as well as symmetrical single cells with PSF/LSF as both anode and cathode were prepared by screen printing.The performances and stability of the cells were examined in different fuels.In order to improve the electrical conductivity of LSF,metallic nanoparticles were incorporated into porous LSF anode by infiltration;and the effect of different metal nanoparticles on the performance of LSF anode was investigated.LSF anode was firstly synthesized and characterized as anode for SOFC.The thermal expansion curve of LSF showed a linear dependent on temperature with the thermal expansion coefficient of 14.3×10-6 K-1,which is close to those of commonly used electrolyte materials.The XPS results showed that Sr content at the surface of LSF was lower than the value in the bulk material in the reducing atmosphere,which would be benefit to the stability of the anode.The presence of Fe+2 and+3 valences may be responsible for the catalytic activity of LSF.The single cell with LSF anode LSF/SDC/ScSZ/SDC/LSFCNb demonstrated excellent catalytic activity and stability in H2,H2S,CO fuels with tolerance to coke and sulfur poisoning.The Pmaxs of the cell achieved 820,480 mW cm-2 in wet H2 fuel,892,601 in 50ppm H2S,and 673,272 mW cm-2 in 50%CO at 900 and800?,respectively.ThePmaxsofasymmetriccell LSF/SDC/YSZ/SDC/LSF with LSF both as cathode and anode in wet H2fuel achieved 594,442,and 301 mW cm-2 at 900,850 and 800?,respectively.Therefore,LSF is a promising anode material for SOFC.Then PSF was synthesized and evaluated as anode for SOFC.Two slopes can be observed for the dependence of polarization resistance Rp of PSF anode in symmetrical half cell in 5%H2 with the reciprocal of temperature,and the activation energy Ea at higher temperature is smaller than the Ea at lower temperature,indicating that the electrocatalytic activity of PSF is thermally activated.The Pmaxs of single cell PSF/SDC/YSZ/SDC/PSFC were 553,370 and 245mW cm-2 with wet H2 as fuel at 900,850 and 800?,respectively.The Pmaxs of a symmetric cell PSF/SDC/YSZ/SDC/PSF with PSF both as cathode and anode in wet H2fuel were 327,246,168 mW cm-2 at 900,850 and 800?,respectively.In order to improve the electrochemical conductivity of LSF anode,metallic?alloy?nanoparticles of Co,Co-Fe,Co-Ni and Fe-Ni are impregnated into the porous LSF anode substrate.The Rp of the composite LSF-M anodes significantly decreased at low and intermediate temperature ranges,and the degree of reduction is relevant to the composition of impregnated metal?alloy?nanoparticles.It is observed that Co-Ni alloy nanoparticles showed the best enhancement on the electrochemical catalytic performance of LSF anode,for example,the anodic polarization resistance at 700?decreases by 94.4%from 7.14?cm2 to 0.40?cm2after infiltration with Co-Ni nanoparticles. |
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