Study On Performance Of Cathode And Interconnect Material For Solid Oxide Fuel Cell

Solid oxide fuel cell (SOFC) is an energy conversion device which can convert fossilenergy into electrical directly without any thermal cycling. Due to its high powerefficiency and environmentally friendly, and along with the energy shortage and theincreasing environmental pollution, the study on SOFCs has grabbed a lot of attention inthe field of energy and materials science. SOFCs have still met a lot of materials andtechnology problems because of its high openration temperature (~1000℃), so reduce theoperating temperature of SOFCs is nessary. Reducing the layer thickness of the electrolyte,optimizing the structure of the battery and preparation technology and developing newmaterials with high conductivities may be an effective approachs. Cathode materials andinterconnector are key component of solid oxide fuel cell, to explore new cathode materialsand the interconnect material to improve electrode properties and enhance its thermalexpansion coefficient (TEC) close to those of the other components of the cell isparticularly important.A layered perovskite oxide SmBaFe2O5+δ(SBFO) is employed as a cathode material forintermediate-temperature solid oxide fuel cells (IT-SOFCs). The XRD results indicate thatSBFO is chemically compatible with SDC at temperatures up to1100°C. The thermalexpansion coefficient (TEC) of SBFO was close to that of SDC electrolyte and theelectrical conductivity of SBFO reaches the maximum value of17.37Scm1at800°C. Thesingle cell consisting of SBFO/SDC/NiO-SDC is operated from500to650°C withhydrogen as fuel and the static air as oxidant that shows an excellent power density of430mW·cm2at650°C. The symmetrical cell with the configuration ofSBFO-SDC/SDC/SBFO-SDC is applied for the impedance study and area specificresistance (ASR) of SBFO cathode material is as low as0.74Ωcm2at650°C. Preliminaryresults confirm that SmBaFe2O5+δ(SBFO) may be promising cathode for IT-SOFCoperation.In order to develop a cathode material for intermediate-temperature solid oxide fuelcells (IT-SOFCs), SmBaCuCoO5+δ(SBCC) powder was prepared via citric acid method.The structure and performance of SBCC cathode were investigated by X-ray diffraction(XRD), electrical conductivity, thermal expansion, alternating current impedancespectroscopy and scanning electron microscopy (SEM). The results show that SBCC hasgood chemical compatibility with the electrolyte Sm0.2Ce0.8O1.9(SDC). The electricalconductivity of SBCC reaches the maximum value of86.0Scm1at800°C. Its thermalexpansion coefficient value (12.3×10-6K–1) is close to those of typical electrolytes such assamaria-doped cerium (SDC) and yettria-stablilzed zirconia (YSZ). The single cellconsisting of Ni-SDC/SDC/SBCC operated from500to650°C with hydrogen as fuel andthe static air as oxidant shows an excellent power density of374mWcm2at650°C, andthe area specific resistance of SBCC cathode material is as low as0.24Ωcm2at650°C. Sm1-xCaxCrO3-δ(x=0,0.1,0.2,0.3,0.4) as new interconnecting materials for solidoxide fuel cells were developed. The ceramic powders with a nominal composition ofSm1-xCaxCrO3-δwere prepared via citric acid method. The powders exhibit good sinteringability and the Ca-doped samples are more compact than SmCrO3after sintering at1400°Cfor5h in air. The average thermal expansion coefficients (TECs) of the Sm1-xCaxCrO3-δspecimens in the temperature range of30~1000°C increase from7.34×10–6to8.05×10–6K–1when x increases from0.1to0.4, which well match with those of the other componentsof SOFC. The most striking of which was the electrical conductivity of Sm0.7Ca0.3CrO3-δis29.8S·cm-1at700°C in air and1.68S·cm-1at600°C in H2, respectively. It suggests thatSm0.7Ca0.3CrO3-δis a good candidate for interconnect material of SOFCs.In this paper, the interconnecting materials for intermediate-temperature solid oxidefuel cells were developed, the ceramic powders with a nominal composition ofNd1-xCaxCrO3-δ(x=0,0.1,0.2,0.3,0.4) were prepared via citric acid method. The electricalconductivity of the Nd0.6Ca0.4CrO3-δis56.4S·cm-1at800°C in air and1.6S·cm-1at800°Cin H2, respectively. The average thermal expansion coefficients (TECs) of theNd1-xCaxCrO3-δ(x=0,0.1,0.2,0.3,0.4) specimens in the temperature range of30~800°Cincreased from6.5×10–6K–1to7.8×10–6K–1when x increased from0.1to0.4, which wellmatches with the other components of SOFC.