Application In Intermediate-temperature Solid Oxide Fuel Cells Research Articles

Structural, electrical and thermal studies on microwave sintered Dy and Pr co-doped ceria ceramics as electrolytes for intermediate temperature solid oxide fuel cells

The present study was focused on the effects of co-doping on the conductivity enhancement of CeO2-based solid ceramics for application as electrolytes in intermediate temperature solid oxide fuel cells (IT-SOFCs) and the correlation of ionic conductivity variations with micro structural alterations resulting from the addition of co-dopants. Nano-crystalline Dy and Pr co-doped ceria Ce0.8Pr0.2−xDyxO2−δ solid solutions were successfully synthesized by sol–gel auto-combustion and innovative densification by energy efficient microwave sintering (MS) at 1300 °C. The XRD results in concurrence with Raman studies ascertained the formation of cubic fluorite structure in the entire range of composition. The lattice parameters obtained by Rietveld refinement showed lattice contraction with increased dysprosium content. MS has resulted in improved densification and the relative densities of all the samples were noticed above 96% of the theoretical density. TEM images confirmed the nano-crystalline character in the as-prepared samples with the particle sizes measured around 20 nm. SEM micrographs showed spherical faceted near-uniform grains (average grain sizes around 225 nm) with distinct grain boundaries and negligible porosity. Formation of oxygen vacancies and their concentration in all the samples was assessed with the help of Raman spectroscopy. Total ionic conductivity values and activation energies were measured depending on the Dy content. The ionic conductivity of the best composition was found to be 6.8 mS cm−1 at 500 °C. Thermal expansion co-efficient of the samples was matched with that of the commonly used electrode materials. These results gave rise to the firm conclusion that the investigated co-doped ceria has the potential to be utilized as an electrolyte for IT-SOFC applications.

Effect of La3+ and Pr3+ co-doping on structural, thermal and electrical properties of ceria ceramics as solid electrolytes for IT-SOFC applications

In the present investigation, the effect of La3+ and Pr3+ co-doping on structural, thermal and electrical properties of ceria ceramics useful as solid electrolytes in intermediate temperature solid oxide fuel cells (IT-SOFCs) has been studied. The co-doped ceria Ce0.8Pr0.2–xLaxO2-δ samples have been prepared successfully via sol-gel auto-combustion synthesis. The high dense ceramic samples have been achieved by carry out an optimized conventional sintering at 1300 °C for 4 h. The powder X-ray diffraction analysis of all the co-doped ceria ceramics revealed the single phase with cubic-fluorite structure formation. Crystallographic information has been carried out from the powder X-ray diffraction and Rietveld refinement analysis. The scanning electron microscope and energy dispersive spectroscopy analysis revealed the smaller grain size with high density in microstructure and stoichiometric elemental confirmations. Raman spectra of prepared ceramics revealed the information of phase and oxygen vacancy formation in the entire compositions. The dilatometric studies of prepared co-doped ceria ceramics revealed the moderate coefficients of thermal expansion. The electrical parameters such as total conductivities and activation energies have been studied with the help of impedance spectroscopy. Among all these co-doped ceria ceramic samples, Ce0.80Pr0.10La0.10O2−δ found to exhibit the highest value of total ionic conductivity with minimum activation energy and this makes it could be a promising electrolyte material for IT-SOFC applications.

Praseodymium doped ceria as electrolyte material for IT-SOFC applications

Praseodymium-doped ceria (PDC, Ce0.9Pr0.1O2) electrolyte material for intermediate temperature solid oxide fuel cells (IT-SOFCs) has been successfully synthesised by EDTA-citrate method. From X-Ray diffraction (XRD), fluorite structure along with a crystallite size of 5.4 nm is obtained for PDC nanopowder calcined at 350 °C/24 h. Raman spectroscopy confirmed the structure, presence of oxygen vacancies with the manifestation of the main peak at 457 cm−1 and with a secondary peak at 550 cm−1. From Transmission Electron Microscopy (TEM) analysis, the average particle size is around 7–10 nm and selected area electron diffraction (SAED) patterns further confirmed the fluorite structure of PDC nanopowder. The PDC nanopowder displayed a BET surface area of 65 m2/g with a primary particle size of ∼13 nm (calculated from BET surface area). Dilatometer studies revealed a multi-step shrinkage behaviour with the multiple peaks at 522, 1171 and 1461 °C which may be originated due to the presence of multiple size hard agglomerates. The PDC electrolyte pellet sintered at 1500 °C displayed an ionic conductivity of 1.213E-03 S cm−1 along with an activation energy of 1.28eV. Instead of a single fluorite structure, XRD of sintered PDC pellet showed multiple structures (Fluorite structure (CeO2) and cubic structure (PrO2).

Insight into the structure and functional application of Mg-doped Na0.5Bi0.5TiO3 electrolyte for solid oxide fuel cells

Na0.5Bi0.5TiO3 (NBT) and its acceptor-doped perovskites, as lead-free piezoelectric materials before, have been found to be excellent oxygen-ion conductors with potential applications in intermediate-temperature solid oxide fuel cells (SOFCs). Among them, the Bi deficient and B-site Mg doped sodium bismuth titanate (Na0.5Bi0.49Ti0.98Mg0.02O2.965, NBTM) exhibits a remarkable oxygen ionic conductivity. Here, we report a structural analysis on NBT and NBTM ceramics using high-temperature in situ neutron diffraction (NPD) to gain insight into the effects of Mg doping on ionic conductivity and structure. Both perovskite oxides exhibit two consecutive phase transformations from R3c to P4bm at ∼400 °C and from P4bm to Pm3¯m at ∼600 °C. The effects of Bi deficiency and Mg substitution on oxygen vacancy concentration and ion displacements are revealed. In addition, a NBTM supported single cell consisting of Ag-NBTM cathode and Ni-NBTM anode is fabricated to evaluate the possibility of its application in intermediate-temperature SOFCs. The structural stability of NBTM is still a major concern that hinders its utilization at high temperature and under reducing atmosphere.

Improvement of ionic conductivity in A-site lithium doped sodium bismuth titanate

Oxide-ion conductors play a significant role in various applications such as solid oxide fuel cells (SOFCs), oxygen separation membranes and sensors. Recently, high ionic conductivity (~1×10−4Scm−1 at 600°C) was found in sodium bismuth titanate (NBT), which originates from oxygen vacancies compensating the introduced Bi-deficiency. By providing pathways with low diffusion barriers, the highly polarizable Bi3+ ions with 6s2 lone pair electrons and weak BiO bonds are also beneficial for the migration of oxygen ions. Here we report the influence of lithium doping on the electrical properties of NBT. The optimal doping level of 4at% Li on the Bi-site improves the ionic conductivity by one order of magnitude to ~7×10−3Scm−1 at 600°C without changing the conduction mechanism, which could be attributed to an increase in the oxygen vacancy concentration based on an acceptor doping mechanism. A further increase in Li content does not improve the total conductivity. Oxygen diffusion data were acquired by the Isotope Exchange Depth Profile (IEDP) method in combination with Secondary Ion-Mass Spectrometry (SIMS). The oxygen self-diffusion coefficients (e.g. 7.04×10−9cm2s−1 at 600°C) are in excellent agreement with the values derived from impedance spectroscopy data, suggesting that the oxygen ions are the main charge carriers in the system. Furthermore, a degradation test was performed for 100h under a variety of atmospheres, showing only a slight decrease in conductivity in both air and oxygen atmospheres attributed to the loss of material from the A-site. Comparison with other oxide-ion conductors indicates that Li-doped NBT materials are promising candidates for intermediate temperature SOFC applications.

Preparation and characterization zirconium and samarium co-doped ceria solid electrolytes for IT-SOFC applications

Zirconium and Samarium co-doped ceria solid electrolyte materials Ce0.8–xSm0.2ZrxO2-δ (x=0, 0.05, 0.10, 0.15 and 0.20) for intermediate temperature-solid oxide fuel cells were synthesized by citrate-nitrate auto combustion synthesis technique. Powder x-ray diffraction results reveal that all the synthesized samples show a single-phase with cubic fluorite structure. The lattice parameter values were calculated from the powder x-ray diffraction data. Samples with high density were obtained by sintering the samples at 1300°C for 4h. The average crystallite sizes were calculated from the Scherer formula. Surface morphologies of all the samples were obtained by using the scanning electron microscope. The total ionic conductivity of all the samples was carried out from impedance analysis in the temperature range RT – 500°C. The highest total ionic-conductivity with lowest activation energy values were observed for Ce0.65Sm0.2Zr0.15O2-δ at 500°C makes it as a useful solid electrolyte material for intermediate temperature-solid oxide fuel cells (IT-SOFCs) applications.

Synthesis, characterization, and electrochemical properties of bi- layered cathode films deposited on co-doped ceria

La0.6Sr0.4Co0.8Fe0.2O3-δ (LSCF) perovskite was studied as a possible cathode material for intermediate-temperature solid oxide fuel cells (IT-SOFC). The LSCF material, prepared using the Pechini method, exhibited chemical compatibility with the Ce0.8Sm0.17La0.03O1.9 (LaSDC) electrolyte up to a temperature of 850 °C. The symmetrical LSCF/LaSDC/LSCF half-cell was studied through structural and morphological analyses. The electrochemical properties of the spin coated and screen-printed LSCF thin and thick porous films on a dense LaSDC electrolyte were measured between 600–700 °C in air over. The electrical properties of a half-cell in air gave low ASR values, 0.032 Ω.cm² at 700 °C and 0.077 Ω.cm² at 650 °C. The results demonstrate that La0.6Sr0.4Co0.8Fe0.2O3/Ce0.8Sm0.17La0.03O1.9 half-cell could potentially be used as good candidate for its application in IT-SOFCs.

Nb-substituted PrBaCo2O5+δ as a cathode for solid oxide fuel cells: A systematic study of structural, electrical, and electrochemical properties

Double perovskite oxides, such as PrBaCo2O5+δ (PBC), are among the most promising cathode materials for intermediate temperature solid oxide fuel cells (IT-SOFCs) thanks to their high catalytic activity and mixed ionic and electronic conductivity. Here, we investigate the impact of Nb substitution on the crystal structure, catalytic activity, and electrical conductivity of PBC. Several studies have outlined that doping high valence cations, such as Nb5+, effectively stabilizes the perovskite structure, decreases the thermochemical expansion coefficient of the material, and can benefit the peak power density of the fuel cell.The as-prepared PrBaCo2−xNbxO5+δ with x = 0, 0.25, 0.50, 0.75, and 1.00 (PBCN) exhibit structural change from P4/mmm (x = 0) to I4/mmm (x = 1), whereas both phases are present for intermediate compositions. The analysis of electrochemical impedance spectroscopy (EIS) data shows that PBCN is characterized by relatively low polarization resistance. Between 300 and 800 °C, the electrical conductivity of PBCN, with x = 0.25, 0.50, lies above 100 S cm−1. If x = 0.75 or 1.00, the conductivity drops below 100 S cm−1. Our work suggests that the Nb-doped PBC exhibits excellent chemical compatibility with typical electrolyte material and good electrochemical performance, making it a promising cathode material for applications in IT-SOFCs.

Erratum to: Synthesis and characterization of La0.595V0.005Sr0.4 CoO3−δ as a novel cathode material for solid oxide fuel cells (SOFC)

The effect of vanadium doping on the crystal structure and on the electrical, electrochemical properties of La0.6−x V x Sr0.4CoO3−δ (x = 0.005–0.05) perovskite oxides performing as cathode materials in solid oxide fuel cells is investigated in this study. Crystal structure, surface morphology, and porosity of prepared cathode materials are characterized by X-ray diffraction, X-ray absorption fine structure, and scanning electron microscopy. For the first time, it has been proven by X-ray absorption fine structure that La3+ cation is replaced with V4+/5+ cation in perovskite structure. Since V4+/5+ cation has the radius almost half of the radius of La3+ cation, this replacement adds better properties to the perovskite structure such as ionic conductivity and catalytic activity for oxygen reduction reaction. The electrical conductivity at the intermediate temperatures (400–700 °C) appears to be enough to yield a better performance in intermediate temperature-solid oxide fuel cells applications. The sample with 0.05% V4+/5+ doping exhibits its maximum electronic conductivity (σ = 843 S.cm−1 at 400 °C) and minimum activation energy (Ea = 0.049 eV). The La0.595V0.005Sr0.4CoO3 material as electrode for symmetric cell configuration was prepared on both surfaces of yttria-stabilized zirconia substrates. Oxygen concentration related polarization experiment suggests that the oxygen adsorption–desorption process or reactions controlled by the atomic oxygen diffusion process followed by a charge transfer are the cathode reaction rate-limiting steps. V4+/5+ ion doped LVxSC (La0.6-xVxSr0.4CoO3−δ x = 0.005-0.05) cathode materials for intermediate temperature-solid oxide fuel cells (IT-SOFC) are synthesized for the first time by sol-gel method. LV05SC cathode with good electro-catalytic activity for ORR can be considered as a potential cathode material for IT-SOFC applications.

Composite Cu-LaFeO3 Conversion Coatings on a 18Cr Ferritic Stainless Steel for IT-SOFC Interconnects: An Investigation on Structure and Formation Mechanism

In this work, a novel iron chemical conversion coating process has been applied to deposit a composite Cu-LaFeO3 perovskite coating layer on a commercial 18Cr ferritic stainless steel for application as Intermediate-Temperature Solid Oxide Fuel Cell (IT-SOFC) interconnect. The conversion process is carried out at 600°C under a CO2 gas atmosphere in a binary eutectic lithium-sodium molten carbonate bath containing lanthanum, magnesium and copper additions in form of their respective oxides. Multi-layer coatings are obtained, with a surface composite layer formed by a dense perovskite polycrystalline thick film with metallic copper particles encased in the perovskite grains grown on a Fe-rich spinel sublayer. Copper oxide additions significantly promote the formation of the LaFeO3 perovskite layer, and the experimental results suggest that galvanic coupling phenomena between the alloy elements and copper take place during the coating formation process. Chemical stability and Cr diffusion barrier properties of the composite coating have been evaluated in air exposure experiments at 700°C for 200 h. The perovskite phase shows high stability after the high temperature exposure, with no detectable sign of Cr diffusion in the layer. Details on functional properties of these composite conversion coatings for IT-SOFC applications will be reported in a subsequent study.

Effects of Sm0.5Sr0.5CoO3-based cathode current-collecting element on the performance of intermediate-temperature solid oxide fuel cells

A new design of cathode current-collecting element (CCCE) based on Sm0.5Sr0.5CoO3, which contains gas channels and an array of truncated-pyramid-shaped contact tips, is synthesized through die pressing followed by a conventional solid-state reaction for intermediate-temperature solid oxide fuel cells (IT-SOFCs). This configuration could not only maintain the high electronic conductivity of the material to ensure the efficiency of current collecting, but also improve the gas diffusion rate at the cathode side. The height h of the channel tips on the CCCEs reaches approximately 60, 120, and 240 μm, respectively, which results in the variation in polarization resistance (RP) more significantly than the contact area of the tips does. The experiments show that the RP of the symmetric cells decreased from 0.267 to 0.060 Ω cm2 at 800 °C after employing the CCCE with modified parameters. In addition, the measured peak power density of the individual cell is enhanced from 111 to 145 mW cm−2 at 800 °C. The results show that the cathode current-collecting elements may be potentially useful for applications in IT-SOFCs.

Characterization and evaluation of Ba-doped BaxSr1−xCo0.9Sb0.1O3−δ as cathode materials for LaGaO3-based solid oxide fuel cells

BaxSr1−xCo0.9Sb0.1O3−δ (BSCSbx, x = 0.0–0.8) are investigated as cathodes for intermediate temperature solid oxide fuel cells (IT-SOFCs). BSCSbx oxides are crystallized in a tetragonal structure with s.g. P4/mmm. XPS analysis shows that Ba doping reduces valence state of Co ions: Co in SrCo0.9Sb0.1O3−δ is prone to Co4+, while Co in Ba doped SrCo0.9Sb0.1O3−δ becomes more prone to Co3+. Oxygen deficiency δ increases with Ba doping even at high temperatures. Conductivity is found to decrease with Ba doping. Thermal expansion coefficient (TEC) decreases from 20.6 × 10−6 K−1 for x = 0.0 to 18.4 × 10−6 K−1 for x = 0.6 at 30–1000 °C. With increasing x from 0.0 to 0.6, polarization resistance (Rp) decreases monotonously, and then increases with further increasing x. The lowest Rp of 0.081 Ω cm2 at 700 °C is obtained for BSCSb0.6 cathode. At 700–850 °C, the Rp of BSCSb0.6 is mainly contributed from electron charge transfer; however, below 700 °C, ion charge transfer plays a more important role in Rp. Maximum power densities of the cell with BSCSb0.6 cathode on 300-μm thick La0.9Sr0.1Ga0.8Mg0.2O3−δ (LSGM) electrolyte attain 306–944 mW cm−2 at 700–850 °C. These results indicate that BSCSb0.6 is a promising cathode for application in IT-SOFC.

Ca and Fe co-doped SmBaCo2O5 + δ layered perovskite as an efficient cathode for intermediate-temperature solid oxide fuel cells

A-site Ca and B-site Fe co-doped SmBa1 − xCaxCo2 − yFeyO5 + δ (x = 0, y = 0; x = 0.25, y = 0; x = 0.25, y = 1.0) layered perovskites are prepared and evaluated as the cathode materials for intermediate-temperature solid oxide fuel cells (IT-SOFCs). The synergistic effects of co-doping on the crystal structure, chemical compatibility with the electrolyte, thermal expansion behavior, electrical conductivity, and electrochemical performance are investigated. Ca and Fe co-doping lowers the thermal expansion coefficient of SmBaCo2O5 + δ. The area specific resistance of the Ca and Fe co-doped sample (SmBa0.75Ca0.25CoFeO5 + δ-GDC) is decreased by 49.3%, compared with that of the undoped sample at 800 °C, based on a GDC electrolyte. Furthermore, the maximum power density of a GDC electrolyte-supported single cell with a SmBa0.75Ca0.25CoFeO5 + δ-GDC cathode is increased by 50.7% at 800 °C. The results indicate that the Ca and Fe co-doping layered perovskite SmBa0.75Ca0.25CoFeO5 + δ is an excellent cathode material for IT-SOFC applications.

Stability, compatibility and performance improvement of SrCo0.8Fe0.1Nb0.1O3−δ perovskite as a cathode for intermediate-temperature solid oxide fuel cells

SrCoO3−δ is a mixed ionic-electronic conductor with multiphase. The structural instability, chemical and thermal incompatibility with the standard electrolytes in this material restrict its widespread applications as electrochemical devices. Here we report the characterization and performance improvement of SrCo0.8Fe0.1Nb0.1O3−δ (SCFN) perovskite as a potential cathode material for intermediate-temperature solid oxide fuel cells (IT-SOFCs). The SCFN material exhibits good chemical compatibility with both La0.9Sr0.1Ga0.8Mg0.2O3−δ (LSGM) and Gd0.1Ce0.9O1.95 (GDC) electrolytes at 950 °C for 10 h. Fe and Nb co-doping significantly improves the structural stability, thermal expansion compatibility, and electrochemical performance of the SCFN material as compared to the undoped SrCoO3−δ and Fe-doped SrCo0.8Fe0.2O3−δ (SCF). The introduction of GDC further improves the thermal compatibility and electrochemical performance of the SCFN–GDC composite cathodes, where the thermal expansion coefficients decrease from 24.5 × 10−6 K−1 for SCFN to 16.8 × 10−6 K−1 for SCFN–50GDC between 30 and 950 °C in air, the corresponding area specific resistances are 0.091 and 0.075 Ω cm2 at 700 °C, respectively. The SCFN and its composites reveal some promising aspects of applications in IT-SOFCs. The SCFN–GDC composites provide a trade-off between TEC and electrochemical performance for application as IT-SOFC cathode materials.

One-step synthesized Co1.5Mn1.5O4-Ce0.8Sm0.2O1.9 composite cathode material for intermediate temperature solid oxide fuel cells

A Co1.5Mn1.5O4-Ce0.8Sm0.2O1.9 (CMO-SDC) composite material has been prepared by the one-step hydrothermal synthesis method. The phase structure and morphology of the polycrystalline powders have been characterized by X-ray powder diffraction (XRD), Scanning Electron Microscopy (SEM). The results show the coexistence of the spinel and the fluorite-type structure which is uniformly distributed throughout the prepared samples. The fluorite phase SDC is well compatible with the spinel phase CMO. This proposed CMO-SDC composite cathode is successfully assembled with a traditional yttria stabilized zirconia (YSZ) electrolyte to fabricate intermediate temperature solid oxide fuel cells (IT-SOFCs) with the structure Ni–YSZ|YSZ|CMO-SDC. The CMO-SDC (50:50wt%) cell with the YSZ film of ~60µm in thickness achieve power densities of 932 and 646mWcm-2 at 800 and 750℃, respectively, in humidified H2 (3vol%H2O), demonstrating its promising application in IT-SOFCs. The high performance is attributed to the intimate contacts between CMO and SDC nanoparticles in the three-phase boundaries in the cathode.

Synthesis and properties of ceria based electrolyte for IT-SOFCs

Fluorite oxides Ce0.8Y0.18M0.02O2 − δ (denoted as MYDC for M = Ca, Sr, Fe and La), were prepared by the sol–gel method used as electrolytes for intermediate-temperature solid oxide fuel cells (IT-SOFCs). X-ray diffraction data show that all the compositions were obtained with highly phase-pure cubic fluorite structure. The relatively density of all the samples sintered at 1400 °C is more than 95%. Surface morphology has been studied by scanning electron microscope showing a dense microstructure. AC impedance spectroscopy measurements have been carried out to study the ionic conductivity of the samples in the temperature range 400–800 °C. In all composition, Ce0.8Y0.18La0.02O2 − δ shows the maximum conductivity of 0.057 S/cm at 800 °C and shows a good prospect of application in IT-SOFCs.

Effect of Thermal Treatment on Structural/Electrical Properties of Protective Oxides for SOFC Metallic Interconnects

For intermediate temperature SOFC applications, metallic interconnects, such as Crofer 22H, have been used to replace ceramic interconnects in SOFC stacks because they are less expensive, more conductive and able to form complex shapes. Most metallic interconnects use chromium-containing alloy that form chromia scales at high temperatures. Since chromia may react with cathode and cause degradation, a protective oxide may be used to suppress the growth of chromia. Several techniques have been adopted to deposit oxides on metallic interconnects, thermal spray is found to be an appropriate technique. Thermal spray coating process has been used to produce a high quality coating by a combination of high temperature, high energy heat source, a relatively inert spraying medium, usually argon, and high particle velocities. This process allows the spraying of various types of metallic or ceramic coatings on to a wide range of substrate materials. As a result, uniform coating layer with excellent bond strength to substrate is obtained without noticeable distortion. However, the temperature during thermal spraying may be high enough to change the crystal structure and conductivity of protective oxides. The heat treatment is believed to be an appropriate method to obtain adequate properties for protective oxide. In this study, conducting oxides were deposited on metallic interconnect using plasma spray technique. However, the deposition temperature for thermal spray coating may be high enough to change the crystal structure and conductivity of protective oxide. The post annealing at elevated temperature is found to be an appropriate method to obtain adequate properties for protective oxide. Thus, the objective of this work is to investigate the effect of annealing on the crystal structure and conductivity of the sprayed oxide. The crystal structure, morphology and electrical conduction of interconnect with sprayed oxide films will be examined by using XRD, FESEM and resistance measurement.

A-site calcium-doped Pr1−xCaxBaCo2O5+δ double perovskites as cathodes for intermediate-temperature solid oxide fuel cells

The LnBaCo2O5+δ (Ln = rare earth) double perovskite cathodes possess superior electrochemical performance in intermediate-temperature solid oxide fuel cells (IT-SOFCs). However, high thermal expansion coefficients (TECs) and material costs are major challenges to their widespread applications. In this paper, a novel A-site Ca doping strategy that can suppress the spin-state transition of Co3+ is proposed to reduce the TECs and material costs of Pr1−xCaxBaCo2O5+δ (x = 0.1–0.4; PCBCO). Substitution of Ca for Pr effectively reduces the TEC from 22.2 × 10−6 K−1 at x = 0.1 to 19.1 × 10−6 K−1 at x = 0.3 between 100 and 800 °C. PCBCO exhibits good chemical compatibility with the Sm0.2Ce0.8O1.9 (SDC) electrolyte. The area-specific resistances of PCBCO cathodes with x = 0.1, 0.2, and 0.3 are 0.081, 0.082, and 0.089 Ω cm2, respectively, at 700 °C on the SDC electrolyte. The maximum power densities of a single cell on a 0.3 mm-thick SDC electrolyte reach 646.5, 636.8, and 620.6 mW cm−2 at 800 °C for cathodes with x = 0.1, 0.2, and 0.3, respectively. The PCBCO double perovskites exhibit excellent chemical compatibility and electrochemical performance while reducing the TECs and material costs; thus, these double perovskites are promising cathode materials for applications in IT-SOFCs.

Synthesis, characterization and thermal expansion of Ce0.8–xSm0.2ZrxO2-δ Solid electrolytes for IT-SOFC applications

The solid electrolyte materials Ce0.8–xSm0.2ZrxO2- (CSZ) (x=0, 0.05, 0.10 and 0.15) for intermediate temperature-solid oxide fuel cells (IT-SOFCs) are prepared by citrate-nitrate auto combustion (CNAC) method. The x-ray diffraction studies of the prepared samples confirm the presence of single phase-cubic fluorite structure with the space group Fm QUOTE m. The calculated average crystallite sizes are found to be in the range of 14 nm to 19 nm. The lattice parameter values are calculated from the XRD patterns. Microstructure analysis and elemental distributions of the composition of the sintered samples are obtained by using the scanning electron microscope (SEM) and energy dispersive spectrum (EDS). The measurements of coefficients of thermal expansion (TECs) are determined from thermal expansion of the CSZ system. The observed TEC values are found to increase with the increase of the doping content of Zr4+. It is found that the thermal expansion coefficients of Zr4+ and Sm3+ co-doped ceria samples match with commonly used electrode materials for IT-SOFCs.

Bismuth and niobium co-doped barium cobalt oxide as a promising cathode material for intermediate temperature solid oxide fuel cells

Perovskite oxides BaBi0.05Co0.95−yNbyO3−δ (BBCNy, 0 ≤ y ≤ 0.2) are synthesized and evaluated as potential cathode materials for intermediate temperature solid oxide fuel cells (IT-SOFCs). Highly charged Nb5+ successfully stabilizes the cubic perovskite structure to room temperature with Nb substituting content y ≥ 0.1. The phase structure, thermal expansion behavior, electrical conductivity and electrochemical performance of BBCNy with cubic phase are systematically studied. The samples exhibit excellent chemical compatibility with GDC and have sufficiently high electrical conductivities. However, the thermal expansion coefficients of BBCNy samples are nearly twice those of the most commonly used electrolyte materials YSZ and GDC, which is a major drawback for application in IT-SOFCs. The polarization resistances of BBCNy with y = 0.10, 0.15 and 0.20 on GDC electrolyte are 0.086, 0.079 and 0.107 Ω cm2 at 700 °C, respectively. Even though the YSZ electrolyte membrane and GDC barrier layer are approximately 50 μm and 10 μm in thickness, the highest maximum power density (1.23 W cm−2) of the single cell Ni-YSZ|YSZ|GDC|BBCN0.15 is obtained at 750 °C. Good long-term stability of the single cell with BBCN0.15 cathode is also demonstrated. These results demonstrate that BBCNy perovskite oxides with cubic structure are very promising cathode materials for IT-SOFCs.