Preparation and performance of Pr-doped Ba_(0.5)Sr_(0.5)Co_(0.8)Fe_(0.2)O_(3-δ) cathode for IT-SOFCs

(Ba0.5Sr0.5)1-xPrxCo0.8Fe0.2O3-δ(BSPCFx;x=0.00-0.30) oxides were synthesized by a sol-gel thermolysis process using combination of PVA and urea,and were also investigated as cathode material for intermediate temperature solid oxide fuel cells(IT-SOFCs).X-ray diffraction(XRD) results showed that all the samples formed a single phase cubic pervoskite-type structure after being calcined at 950 oC for 5 h and the lattice constant decreased with the Pr content increasing.The electrical conductivity of Ba0.5Sr0.5Co0.8Fe0.2O3-δ(BSCF) was greatly enhanced by Pr-doping.The thermal expansion coefficient(TEC) of BSPCFx was increased with the content of Pr increasing,and all the thermal expansion curves had an inflection at about 250-400 oC due to the thermal-induced lattice oxygen loss and the reaction of Co and Fe ion.Ac impedance analysis indicated that BSPCFx possessed better electrochemical performance.The polarization resistance of the sample with x=0.2 was only ～0.948 Ω cm2 at 500 oC,significantly lower than that of BSCF(～2.488 Ω cm2).     

Characterization and Stability of La0.5Sr0.5CoO2.91 Perovskite-Type Oxide

Compositely doped oxide La0.5Sr0.5CoO2.91 （LSC） was synthesized using solid state reaction and citric acid-nitrate low temperature self-propagating combustion methods. The crystal structure and the particle size micrograph of LSC powders synthesized by different methods were investigated with XRD and SEM. The experimental results show that the single perovskite phase of LSC can be synthesized by solid state reaction method, but LaSrCoO4 phase appears in LSC powder synthesized by citric acid-nitrate low temperature self-propagating combustion method. The LSC particle by citric acid-nitrate low temperature self- propagating combustion method has smaller size. To analyze the character of cathode material based on Ceo.gGdo.101.95（GDC） electrolyte, two types of cathode wafers were fabricated with the two kinds of LSC and GDC powders at the mass rate of 6：4, respectively. The electrical conductivity of the sintered samples was measured by four probe DC method from 300 to 800 ℃. The cathode with LSC particle by citric acid- nitrate low temperature self-propagating combustion method has higher electrical conductivity. In order to investigate the stability, the two samples were put into the muffle furnace to heat up in air at 800℃for 800 h. To analysis the reason for reduced electrical conductivity, the crystal structure and the particle micrograph of the cathode wafers before and after an exposure were investigated with XRD and SEM. The result shows that new crystal structure appears in both the two kinds of cathode wafers and crystal micrographs change a lot.     

Electrical Properties and Microwave Synthesis of Mixed Rare Earth Oxide Ln0.7Sr0.3-xCaxCo0.9Fe0.1O3-δ

In order to lower the raw materials cost and develop a novel cathode materials for intermediate temperature solid oxide fuel cell(ITSOFC), using mixed rare earth replacing the expensive pure La2O3 as the raw materials, the powders of Ln0.7Sr0.3-xCaxCo0.9Fe0.1O3-δ (Ln=the mixed rare earth, x=0.05, 0.10, 0.15) for the applications as the cathode materials were prepared by microwave sintering process. The crystal structure and the particles morphology of the obtained powders were characterized by XRD and SEM, the electrical conductivity of all samples sintered at 1200 ℃ for 3 h was also measured as the function of the temperature from 100 to 800 ℃ by DC four-probe method in air. The experimental results show that due to the influence of mixed rare earth the powders of Ln0.7Sr0.3-xCaxCo0.9Fe0.1O3-δ synthesized at 1200 ℃ for 0.5 h with the mean particle size of 1～20 μm was of perovskite and cubic fluorite phase as well a little SrO phase, the electrical conductivity of the samples decreases with the adding Ca2+ content, and are all higher than 100 S·cm-1 from 500 to 700 ℃ when x≤0.10. Ln0.7Sr0.3-xCaxCo0.9Fe0.1O3-δ. Can meet the demand of the electrical properties for the cathode materials in ITSOFC.     

Microwave assisted synthesis,sinterability and properties of Ca-Zn co-doped LaCrO_3 as interconnect material for IT-SOFCs

The interconnect materials La0.7Ca0.3Cr1-xZnxO3-δ(x=0,0.01,0.03,0.05,0.07) were prepared by a microwave assisted sol-gel auto-ignition process.The crystalline structures of the samples were characterized by X-ray diffraction(XRD) and the lattice parameters were evaluated with Rietveld method.For Ca-Zn co-doped LaCrO3 with x=0.03,the sintering activity was improved,and the relative density came up to 96.5% for the sample sintered at 1300 oC for 10 h.The electrical conductivity of the samples was increased from 21.1 S/cm to the maximum of 70.9 S/cm at 650 oC in air,with the x content increasing from 0.01 to 0.03.However,with x further increasing,the electrical conductivity was decreased.The average thermal expansion coefficient(TEC) of the samples at RT-1000 oC in air was ca.10.0×10-6 K-1.All data indicated that the La0.7Ca0.3Cr1-xZnxO3-δ series ceramics would be potential candidate to be used as an interconnect materials for IT-SOFCs.     

Effect of samarium filling on the lattice thermal conductivity of skutterudite materials

Sm-filled skutterudites SmxCo4Sb12 (x=0.1, 0.2, 0.5) were synthesized via high pressure and high temperature (HPHT) technique. The temperature dependences of electrical resistivity, Seebeck coefficient and thermal conductivity were measured on these compounds in the range of 300-723 K. All samples showed n-type conduction. The thermal conductivity of SmxCo4Sb12 was significantly depressed as com-pared to unfilled CoSb3. It was believed that Sm atoms "rattled" in the voids of structure and substantially affected the phonon propagation through the lattice. The dimensionless thermoelectric figure of merit, ZT, increased with increasing temperature and reached a maximum value of 0.81 for Sm0.5Co4Sb12 at 723 K.     

Synthesis and Electrical Properties of La0.6M0.4FeO3-δ(M=Ca, Sr, Ba) as Cathodes for SOFCs

A series samples of La0.6M0.4FeO3-δ (M=Ca, Sr, Ba) perovskite-type oxides were prepared by glycine nitrate process (GNP). FTIR, TG-DSC, XRD and TEM techniques were used to characterize the chemical constitution, thermal stability and phase structure. The electrical conductivity of the samples was investigated by four-probe technique. With the increase of substituted-ionic radius, the temperature of phase formation increases, and the solid solubility decreases gradually, respectively. The La0.6Ca0.4FeO3-δ(LCF)powder is pure cubic perovskite-type crystalline after fired at 850 ℃ for 2 h. The XRD patterns of La0.6Sr0.4FeO3-δ(LSF) powder shows a small quantity of SrO peaks sintered at 1050 ℃ for 2 h. The electrical conductivity of LCF and LSF at 500～800 ℃ is over 100 S·cm-1, and the value of LCF is 1170 S·cm-1 at 800 ℃, which indicate that LCF and LSF may be used as a profitable cathode for IT-SOFCs. The characteristic of La0.6Ba0.4FeO3-δ(LBF) is poor, and the electrical conductivity at intermediate temperatures is 1/20 less than that of LSF.     

Solid state reaction synthesis and total electrical conductivity of La_(0.7)Sr_(0.3)Cr_yMn_zCo_(1-y-z)O_(3-δ)

The La0.7Sr0.3CryMnzCo(1-y-z)O3-δ samples were prepared by solid state reaction.The phases,microstructure and properties of the samples were investigated by XRD,SEM,DC four-probe method and iodometry method.The single orthorhombic phase La0.7Sr0.3CryMnzCo(1-y-z)O3-δ perovskite oxides were obtained when sintered at l350 °C for 10 h.The oxygen nonstoichiometry of the materials varied inversely with the total electronic conductivity.The sample with composition of La0.7Sr0.3Cr0.5Mn0.35 Co0.15O3-δ had the maximal total electronic conductivity and the lowest oxygen nonstoichiometry which were 22.4 S/cm and 0.040 at 850 °C,respectively.The low total electronic conductivity is related to the low relatively density of the samples directly.The activation energy of conduction changed at 550 °C,and the activation energy of conduction at high temperature(T550 °C) was higher than that at low temperature range(T550 °C).     

Fabrication, characterization, and electrical conductivity properties of Pr6O11 nanoparticles

Pr6O11 nanoparticles were obtained by subsequent thermal decomposition of the as-prepared precipitate formed under ambient temperature and pressure using NaOH as precipitant.The calcination process was affected,for 1 h in static air atmosphere,at 400-700 °C temperature range.The different samples were characterized using X-ray diffraction(XRD),transmission electron microscopy(TEM),field emission scanning electron microscopy(FE-SEM),thermogravimetric analysis(TGA),in situ electrical conductivity,and N 2 adsorption/desorption.The obtained results demonstrated that nano-crystalline Pr6O11,with crystallites size of 6-12 nm,started to form at 500 °C.Such value increased to 20-33 nm for the sample calcined at 700 °C.The as-synthesized Pr6O11 nanoparticles presented high electrical conductivity due to electron hopping between Pr(III)-Pr(IV) pairs.     

Thermoelectric properties of Yb x Co_4 Sb_（12） system

Yb x Co 4 Sb 12 polycrystals were fabricated by vacuum melting combined with hot-press sintering.The effect of Yb-filling on thermoelectric property of unfilled skutterudite CoSb 3 was investigated,which indicated the enhancement of the power factor of the material.Transport properties of materials changed from semi-conductor to semi-metal during the measurement of electrical conductivity,which indicated the change of electronic band structure.The maximum value of electrical conductivity was about 190000 S/m at 300 K for all samples.On the basis of Yb-filling,power factor of Yb 0.2 Co 4 Sb 12 reached 5-6 mW/(m·K) during the measurement temperature.Thermal conductivity decreased with increase of Yb content,and the thermal conductivity of Yb 0.2 Co 4 Sb 12 reached 3.2 W/(m·K) at 600 K.The ZT value of Yb 0.2 Co 4 Sb 12 reached 1.16 at 700 K due to positive contribution from high power factor and low thermal conductivity.     

Preparation and Characterization of Component Materials for Intermediate Temperature Solid Oxide Fuel Cell by Glycine-Nitrate Process

La1-xSrxGa1-yMgyO3-δ (LSGM) electrolyte, La1-xSrxCr1-yMnyO3-δ (LSCM) anode and La1-xSrxFe1-yMnyO3-δ (LSFM) cathode materials were all synthesized by glycine-nitrate process (GNP). The microstructure and characteristics of LSGM, LSCM and LSFM were tested via X-ray diffraction(XRD), scanning electron microcopy (SEM), A C impedance and four-probe direct current techniques. XRD shows that pure perovskite phase LSGM electrolyte and electrode (LSCM anode and LSFM cathode) materials were prepared after being sintered at 1400 ℃ for 20 h and at 1000 ℃ for 5 h, respectively. The max conductivities of LSGM (ionic conductivity), LSCM (total conductivity) and LSFM (total conductivity) materials are 0.02, 10, 16 S·cm-1 in the air below 850 ℃, respectively. The conductivity of LSCM becomes smaller when the atmosphere changes from air to pure hydrogen at the same temperature and it decreases with the temperature like metal. The porous and LSGM-based LSCM anode and LSFM cathode films were prepared by screen printing method, and the sintering temperatures for them were 1300 and 1250 ℃, respectively. LSGM and electrode (LSCM and LSFM) materials have good thermal and chemical compatibility.     

Transport properties of Zintl phase Yb1-xCaxCd2Sb2 at low temperature

We investigated the transport properties of isoelectronic substitution of Yb by Ca for Zintl phase YbCd2Sb2 below 300 K.The p-type Yb1-xCaxCd2Sb2(0.2≤x≤0.8) samples were synthesized via a solid-state reaction followed by suitable cooling,annealing,grinding,and spark plasma sintering(SPS) densification processes.For samples with x=0.2,0.4,0.5,0.6,0.8,the electrical conductivity,Seebeck coefficient,thermal conductivity,heat capacity and Hall effect measurements were carried out in the temperature range from 1...     

Effect of Y-filling on thermoelectric properties of CoSb3

The CoSb3 and Y0.18Co4Sb12 compounds were synthesized by a metallurgical route. Their bulk materials were prepared by the hot-pressed process under vacuum. Thermoelectric properties of the samples were measured by the thermoelectric measurement system and the laser flash diffusivity apparatus. The carrier type conversion of hot-pressed CoSb3 was found at about 530 K, while the conversion was missed for the Y0.18Co4Sb12 sample. Electrical conductivity of the Y0.18Co4Sb12 sample increased due to the increase of carrier concentration, and its thermal conductivity decreased due to the enhancement of phonon scattering. The value of ZT, figure of merit, for the Y0.18Co4Sb12 sample was obviously enhanced due to positive contribution of the electrical conductivity and the thermal conductivity.     

High-temperature thermal properties of yttria fully stabilized zirconia ceramics

In this study,the dependences of yttria content,porosity and grain size on the thermal properties of Y2O3 stabilized ZrO2 (YSZ) ceramics were investigated.YSZ ceramics were synthesized by the solid state reaction method.The phase,microstructure and thermal properties of YSZ ceramics were characterized by X-ray diffraction (XRD),scanning electron microscopy (SEM),differential scanning calorimetry (DSC) and laser-flash apparatus (LFA),respectively.The results indicated that the specific heat capacity of YSZ increased with the increase of temperature and decreased with the increase of yttria content.As the temperature increased,the thermal diffusivity and conductivity of YSZ ceramics were decreased,whereas their variations for 16YSZ,18YSZ and 20YSZ were much less pronounced than those for 12YSZ and 14YSZ.At a given temperature,the thermal conductivity of YSZ was opposite to yttria content.The thermal conductivity of YSZ ceramics almost linearly decreased with the increase of porosity.In addition,the grain size also had a great influence on the thermal conductivity.     

Electrical Properties and Applications of （ZrO2）0.92 （Y2O3）0.08 Electrolyte Thin Wall Tubes Prepared by Improved Slip Casting Method

8%(mole fraction) yttria-stabilized zirconia electrolyte thin wall tubes were prepared by improved slip casting method. The length and wall thickness of the tubes are 266 mm and 0.4 - 0.9 mm, respectively and the relative density is 96.7 %. The microstructure and electrical properties of samples sintered at different temperatures were studied using SEM and ac impedance spectroscopy. The effect of sintered density, grain and grain boundary on the electrical properties of the samples was analyzed. The research results show that the density of the samples increases gradually with increasing sintering temperatures. The microstructurc of samples strongly influences its electrical properties, and the electrical prop.erties of samples enhance with the increase of sintered density. The ionic conductivity of grain and grain boundary is increased as the sintering temperature increases. Better sinterability of the samples was obtained at the sintering temperature of 1650℃. The maximum open circuit voltage and short circuit current for single cell is 0.946V and 1.84A, respectively. The maximum output power of single cell is 0.46W at the temperature of 850℃.     

Preparation and Electrical Transport Properties of Perovskite Oxide Ln0.5Sr0.5CoO3

The superfine powders of Ln0.5 Sr0.5 CoO3 （Ln = La, Pr, Nd, Sm, Eu） were obtained by solid state reactions. The crystal structure and electrical transport properties of samples doped with different rare earth elements as well as the forming process of the Perovskite structure were studied. The result shows that when the temperature reaches 1200 ℃, the samples will become a steady and unitary Perovskite phase by solid state reactions. The conductive behavor at low temperature is consistent with small polaron mechanism （i. e., localized electronic carriers having a thermally activated mobility）. However, the maximum of conductivity appears at about 700 ℃, and the conductivity of La0.5Sr0.5CoO3 is the biggest in the intermediate-temperature （600 - 850 ℃ ）, so it is fit for cathode material of intermediate-temperature solid oxide fuel cells.     

Preparation and thermoelectric transport properties of Ba-, La- and Ag- doped Ca3Co4O9 oxide materials

The Ba-, La- and Ag-doped polycrystalline Ca2.9M0.1Co4O9 (M=Ca, Ba, La, Ag) thermoelectric bulk samples were prepared via citrate acid sol-gel synthesis method followed by spark plasma sintering technique. The bulk samples were characterized and analyzed with regard to their phase compositions, grain orientations as well as microstructures. The high temperature thermoelectric transport properties of the bulk samples were studied in detail. All bulk samples were found to be single-phased with modified body texture. The electrical resistivity was modulated as a result of carrier concentration modification, however the carrier transport process was not influenced; the Seebeck coefficient was deteriorated simultaneously. The total thermal conductivity was remarkably reduced, on account of the decreasing of phonon thermal conductivity. The thermoelectric properties of the Ba-, La-, and Ag-doped bulk samples were optimized, and the Ba-doped Ca2.9Ba0.1Co4O9 system was found to have the highest dimensionless figure of merit ZT0.20 at 973K, which was remarkably higher than that of the un-doped sample.     

Effects of praseodymium doping on thermoelectric transport properties of CaMnO3 compound system

The rare earth Pr doped Ca1-x Prx MnO3(x=0,0.06,0.08,0.1,0.12,and 0.14) compound bulk samples were prepared to study the effect of Pr doping on thermoelectric transport properties of CaMnO3 compound system.The doped samples exhibited single phase composition within the experimental doping range,with condensed bulk microstructure and small porosities.The electrical resistivity was remarkably reduced for doped samples,on account of the enhanced carrier concentration;the absolute value of Seebeck coefficient was deteriorated mainly due to enhanced electron carrier concentration.The electrical performances of the doped samples reflected by resistivity and Seebeck coefficient fluctuations were optimistically tuned,with an optimized power factor value of 0.342 mW/(m·K2) at 873 K for x=0.08 sample,which was very much higher comparing with that of the un-doped sample.The lattice thermal conduction was really confined,leading to distinctly repressed total thermal conductivity.The thermoelectric performance was noticeably improved by Pr doping and the dimensionless figure of merit ZT for the Ca0.92 Pr0.08 MnO3 compound was favorably optimized with the maximum value 0.16 at 873 K.     

Preparation of Sr_2Fe_(1-x)Sc_xMoO_(6-δ) nanopowders and its electrical conductivity

Double-perovskite Sr2Fe1-xScxMoO6-δ (x=0, 0.05, 0.1, 0.2, 0.3, 0.4) powders applied to the cathode of solid oxide electrolysis cells were synthesized by the sol-gel citrate combustion method. Initial powders were calcined at different temperatures under different atmosphere (air, H2(4 vol.%)/Ar), and the effects of the preparation process on the structure and the morphology of the powders were investigated by thermal analysis (TG/DSC), X-ray diffraction (XRD), scanning electron microscopy (SEM) and surface area analysis. The electric conductiv-ity of the materials was measured by electrochemical work station using wafers prepared by dry pressing. It was found that the formation of perovskite structure was related to the content of Sc and combustion improver (NH4NO3), pH value, calcining temperature and atmosphere. A single perovskite phase of Sr2Fe1-xScxMoO6-δ could be formed after 3 h calcining in reducing atmosphere of H2 (4 vol.%)/Ar at 1100 oC. The electrical property indicated that, this material had a potential to be used in medium/high temperature solid oxide fuel cells or electrolysis cells.     

Fabrication and Characterization of SOFC Anode, Ni-SDC Cermet

NiO and Ce0.8Sm0.2O1.9 were synthesized by the combination of sol gel and citric acid-nitrate low temperature self-propagating combustion method. Anode precursors which include home-made NiO and Ce0.8Sm0.2O1.9 were prepared by different NiO content and fabrication condition. The anode precursors with pure hydrogen at 820 ℃ for 2.5 h were reduced, The electrical conductivity was tested, and the effect of microstructure on electrical conductivity of Ce0.8Sm0.2O1.9 composite anodes was investigated. The results show that the anode electrical conductivity depends strongly on the anode microstructure that is dramatically affected by Ni content and fabrication condition.     

Surface composition change of chlorine-doped catalyst Ni(Cl_x)/CeO_2 in methanation reaction

The oxide sample NiO/CeO_2 with feed atomic ratio of Ni/Ce at 40%, prepared by co-precipitation method and calcination at 500 oC for 2 h, was impregnated by aqueous solution of NH_4Cl to dope chlorine ions. After the impregnated samples were dried and calcined at 400 oC for 2 h, the calcined samples NiO(Cl_x)/CeO_2(x=0.1–0.5) were characterized by means of X-ray diffraction(XRD) and temperature programmed reduction(TPR) techniques. It was comfirmed that the doped chlorine ions hindered reduction of Ni~(2+) ions in the calcined samples, and suppressed adsorption of CO_2 and CO on the reduced sample Ni(Cl_(0.3))/CeO_2. The reduced samples Ni(Cl_x)/CeO_2(x=0.0–0.5) were used as catalysts for selective methanation of CO in H_2-rich gas. When chlorine ions were doped at the feed atomic ratio of Cl/Ce(x) equal to 0.3–0.5, CO in the H_2-rich gas could be removed to below 10 ppm with a high selectivity more than 50% in a wide reaction temperature range of 220–280 oC. However, the selectivity of CO methanation decreased with reaction time in the durability tests over the catalyst Ni(Cl_(0.3))/CeO_2 at the reaction temperature of 260 oC and even at 220 oC. The lowering of the selectivity was found to be related with the surface composition change of the catalyst in the catalytic reaction.