Sm-doped Ceria Research Articles

La0.85Sr0.15Cr0.9Ni0.05Pd0.05O3 Perovskite Anode for SOFC

A Pd doped perovskite La0.85Sr0.15Cr0.9Ni0.05Pd0.05O3 (LSCNP) was investigated as a candidate for a metal-free anode material of solid oxide fuel cell. The deposition and the solid dissolution by reduction and oxidation treatment were observed by FE-SEM and the change of crystal structure was observed by XRD. The performance of anode prepared by mixing LSCNP and Sm doped ceria (SDC) was measured using H2 and dry CH4 as fuel. The anode voltage gradually decreased during the power generation, but recovered by oxidation treatment. Electrochemical impedance spectra were measured and the interfacial resistance increased during the power generation, but it decreased by oxidation treatment. The recovery of the performance due to the deposition and solid solution was confirmed. The performance of LSCNP-SDC anode using dry CH4 as fuel showed a maximum at 5ccm, and the maximum current density was 500 mA cm–2. From the impedance spectroscopy, it was revealed that when the flow rate was high, the relatively low water vapor pressure diminished the reforming reaction, whereas when the flow rate was low, the insufficient supply of fuel increased the diffusion resistance.

Synthesis and electrochemical performance of La 0.6Ca 0.4Fe 1− xNi xO 3 ( x = 0.1, 0.2, 0.3) material for solid oxide fuel cell cathode

Polycrystalline samples of La 0.6Ca 0.4Fe 1− x Ni x O 3 ( x = 0.1, 0.2, 0.3) (LCFN) are prepared by liquid mix method. The structure of the polycrystalline powders is analyzed with X-ray powder diffraction data. The XRD patterns are indexed as the orthoferrite similar to that of LaFeO 3 having a single phase with orthorhombic perovskite structure ( Pnma). The morphological characterization is performed by scanning electron microscopy (SEM) obtaining a mean particle size less than 300 nm. Polarization resistance is studied using two different electrolytes: Y-stabilized zirconia (YSZ) and Sm-doped ceria (SDC). Electrochemical impedance spectroscopy (EIS) measurements of LCFN/YSZ/LCFN and LCFN/SDC/LCFN test cells are carried out. These electrochemical experiments are performed at equilibrium from 850 °C to room temperature, under both zero dc current intensity and air. The best value of area specific resistance (ASR) obtained is 0.88 Ω cm 2, corresponding to the La 0.6Ca 0.4Fe 0.9Ni 0.1O 3 material using SDC as electrolyte. The dc four-probe measurement indicates that La 0.6Ca 0.4Fe 0.9Ni 0.1O 3 exhibits fairly high electrical conductivity, over 300 S cm −1 at T > 500 °C.

Fuel-flexible operation of a solid oxide fuel cell with Sr 0.8La 0.2TiO 3 support

Solid oxide fuel cells with Sr 0.8La 0.2TiO 3 anode-side supports, Ni- Sm-doped ceria adhesion layer, Ni- Y 2O 3-stabilized ZrO 2 (YSZ) anode active layer, YSZ electrolyte, and La 0.8Sr 0.2MnO 3(LSM)–YSZ cathode are described. These cells are stable in simulated natural gas at current densities as low as 0.2 A cm −2. This represents much-improved stability against coking in natural gas, compared with conventional Ni–YSZ anode-supported SOFCs which rapidly coke, even at higher current densities. Cell operation in H 2 fuel with 50–100 ppm, H 2S results in an initial decrease in cell power density, but no long-term degradation occurs and full recovery to the initial performance level is observed after dry H 2 fuel flow is restored. Degradation is not observed during or after seven redox cycles between H 2 and air.

Effect of Tb co-dopant on the electrical conductivity of Sm-doped ceria electrolyte

Series of solid solutions of (Ce 0.85Sm 0.15) 1 − x Tb x O 2 − δ with x = 0–0.05 were synthesized by glycine–nitrate process. All prepared (Ce 0.85Sm 0.15) 1 − x Tb x O 2 − δ ( x = 0–0.05) powders were sintered at 1250 °C, 1350 °C and 1450 °C, respectively. X-ray diffraction patterns indicate that all samples crystallize to a single phase of cubic fluorite structure. Higher sintering temperature was found to give lower electrical conductivity and higher activation energy for (Ce 0.85Sm 0.15) 1 − x Tb x O 2 − δ ( x = 0–0.05). The lower sintering temperatures suppress grain growth giving rise to small grain size. The samples sintered at lower temperatures showed higher grain boundary conductivities, which results in the increasing of total electrical conductivity. The change of electrical conductivities of solid solutions for (Ce 0.85Sm 0.15) 1 − x Tb x O 2 − δ ( x = 0–0.05) was not obvious, and the maximum conductivity was found at x = 0.01 when sintered at1250 °C. The reason may be that co-doping 0.01 terbium in doped ceria will increase the oxygen vacancy concentration slightly, increasing dopant concentration, the oxygen vacancy V o and the dopants Tb′ Ce and Sm′ Ce tend to associate and form [ V o Tb′ Ce] and [ V o Sm′ Ce] pairs, resulting in a decrease in [ V o].

Optimization on technical parameters for fabrication of SDC film by screen-printing used as electrolyte in IT-SOFC

Sm-doped Ceria (SDC) electrolyte film was successfully fabricated on anode substrate of NiO-SDC by screen-printing. Some technical parameters for fabrication were investigated and optimized, including printing times, ink composition and sintering temperature. Scanning electron microscope (SEM) measurement was done to check the microstructures of SDC film and single cell. The parameters greatly affected the quality of SDC film and cell performance. The single cell with the optimum parameters exhibited an OCV of 0.82 V and a power density of 0.5 W/cm 2 at 600 °C.

Catalytic modification of Ni–Sm-doped ceria anodes with copper for direct utilization of dry methane in low-temperature solid oxide fuel cells

A Cu/Ni/Sm-doped ceria (SDC) anode has been designed for direct utilization of dry methane in low-temperature anode-supported solid oxide fuel cells. The anode is prepared by the impregnation method, whereby a small amount of Cu is incorporated into the previously prepared Ni/SDC porous matrix. After reduction, Cu nanoparticles adhere to and are uniformly distributed on the surface of the Ni/SDC matrix. For the resulting Cu/Ni/SDC anode-supported cell, maximum power density of 317mWcm−2 is achieved at 600°C. The power density shows only ∼2% loss after 12-h operation. The results demonstrate that the Cu/Ni/SDC anode effectively suppresses carbon deposition by decreasing the Ni surface area available and the level of carbon monoxide disproportionation. This combination of effects results in very low-power density loss over the operating time.

Optimization of the interface polarization of the La 2NiO 4-based cathode working with the Ce 1– xSm xO 2– δ electrolyte system

The performance of La 2NiO 4 cathode material and Ce 1– x Sm x O 2– δ ( x = 0.1, 0.2, 0.3, 0.4) electrolyte system was analyzed. Ceria-based materials were prepared by the freeze-drying precursor route whereas La 2NiO 4 was prepared by the nitrate–citrate procedure. Electrolyte pellets were obtained after sintering the powders at 1600 °C for 10 h. Also dense ceria-based electrolytes samples were obtained by calcining the powders at 1150 °C after the addition of 2 mol%-Co. Interface polarization measurements were performed by impedance spectroscopy in air at open circuit voltage, using symmetrical cells prepared after the deposition of porous La 2NiO 4-electrodes on the Ce 1– x Sm x O 2– δ system. X-ray diffraction (XRD) of cathode materials after using in symmetrical cells confirmed no significant reaction between La 2NiO 4 and ceria-based electrolytes. The efficiency of the cathode material is highly dependent on the composition of the electrolyte, and low-content Sm-doped ceria samples revealed an important decrease in the performance of the system. Differences in electrochemical behaviour were attributed principally to the oxide ion transference between cathode and electrolyte, and were correlated to the conductivity of the electrolyte. In this way cobalt-doped electrolytes with a Sm-content ≤30% perform better than free-cobalt samples due to the increase in grain boundary conductivity. Finally, composites of the ceria-based materials and La 2NiO 4 to use as cathode were prepared and an important increase of the interface performance was observed compared to La 2NiO 4 pure cathode. Predictions of maximun power density were obtained by the mixed transport properties of the electrolytes and by the interface polarization results. The use of composite materials could allow to increase the performance of the cell from 170 mW cm −2 for pure La 2NiO 4 cathode, to 370 mW cm −2 for La 2NiO 4–Ce 0.8Sm 0.2O 2– δ cathode, both working with Ce 0.8Sm 0.2O 2– δ electrolyte 300 μm in thickness and Ni–Ce 0.8Sm 0.2O 2– δ as anode at 800 °C.

Synthesis, electrical and electrochemical properties of Ba 0.5Sr 0.5Zn 0.2Fe 0.8O 3− δ perovskite oxide for IT-SOFC cathode

The Ba 0.5Sr 0.5Zn 0.2Fe 0.8O 3− δ (BSZF) complex oxide with cubic perovskite structure was synthesized and examined as a new cobalt-free cathode for intermediate-temperature solid oxide fuel cells (IT-SOFCs). The electrical conductivity was relatively low with a peak value of 9.4 S cm −1 at about 590 °C, which was mainly caused by the high concentration of oxygen vacancy and the doping of bivalent zinc in B-sites. At 650 °C and under open circuit condition, symmetrical BSZF cathode on Sm-doped ceria (SDC) electrolyte showed polarization resistances ( R p) of 0.48 Ω cm 2 and 0.35 Ω cm 2 in air and oxygen, respectively. The dependence of R p with oxygen partial pressure indicated that the rate-limiting step for oxygen reduction was oxygen adsorption/desorption kinetics. Using BSZF as the cathode, the wet hydrogen fueled Ni + SDC anode-supported single cell exhibited peak power densities of 392 mW cm −2 and 626 mW cm −2 at 650 °C when stationary air and oxygen flux were used as oxidants, respectively.

A cathode-supported SOFC with thin Ce0.8Sm0.2O1.9 electrolyte prepared by a suspension spray

Abstract In order to develop a cost-effective route to fabricate solid oxide fuel cells (SOFCs), a dense Ce 0.8 Sm 0.2 O 1.9 (SDC) electrolyte was fabricated on a porous cathode based on a mixed conducting La 0.8 Sr 0.2 FeO 3− δ (LSF) via a suspension spray/co-firing process. For the purpose of shrinkage matching between the cathode support and the electrolyte membrane, nano-SDC1 powder for the easily sinterable electrolyte was synthesized with ammonia as the precipitant from the nitrates, whereas SDC2 powder prepared by modified glycine–nitrate method (GNP) was added into cathode to favor the shrinkage of La 0.8 Sr 0.2 FeO 3− δ (LSF) . Sm-doped ceria solid solution was directly formed during precipitation at 50 °C, and this is ascribed to the role of OH − . The powders calcined at 800 °C for 2 h were still uniform and exhibited an average particle size of 20 nm. The bi-layer with 10 μm dense SDC electrolyte was obtained by co-sintering at 1250 °C for 5 h. A thin and well-adherent anode was formed by depositing ultra-fine NiO–SDC powders, followed by sintering at 1000 °C. The obtained single cells were tested with humidified (3% H 2 O) hydrogen as fuel and the static air as oxidant. The maximum power density reached 67.2 mW/cm 2 at 600 °C.

Preparation of Sm-doped ceria (SDC) nanowires and tubes by gas–liquid co-precipitation at room temperature

Sm-doped cerium dioxide (SDC) with fcc structure was formed using a gas–liquid chemical co-precipitation process at room temperature. Morphology and structure of the as-prepared samples were characterized using TG, XRD, TEM, HRTEM and SAED techniques. Under our specific experimental conditions, two kinds of 1D nano-structures SDC have been mainly obtained. SDC nanowires are 0.3–1.2 μm in lengths and 5–20 nm in diameters. SDC nanotubes have outer diameters in 10–40 nm with lengths up to 2 μm. The as-prepared SDC shows very strong UV absorption ability and the maximum absorption peak redshifts compared with that of SDC nanoparticles.

Nano-metal Dispersed Anode of Intermediate-temperature SOFC for High Power Density Operation

Improvements of the anode and the fuel side current collector has been carried out in order to increase the output power of the intermediate-temperature (IT) solid oxide fuel cells (SOFCs) using lanthanum gallate electrolyte. Dispersion of nano-size metal in the cermet anode composed of Sm doped ceria (SDC) and Ni has been tried. As a source material to manufacture the novel anode, SDC powder incorporated with nano-size Ru particles was developed. In order to achieve in-situ production of hydrogen inside the cell-stack, fuel side current collectors were impregnated with catalyst metals such as Ru or Ni. It was demonstrated experimentally that the developed current collectors have high catalytic activity for steam reforming reaction of methane and also have favorable effect to increase the power density. Replacement of the dopant to ceria from Sm to Gd is also tested both for the anode and the fuel side current collector.

Synthesis and Performance of La0.6Ca0.4Fe0.8Ni0.2O3-δ Material for Intermediate-Temperature SOFC Cathode

A major research goal on solid oxide fuel cells (SOFC) is to develop cost-effective component materials for operation temperatures lower than 800ºC. In this way, the La0.6Ca0.4Fe0.8Ni0.2O3-δ (LCFN) phase with perovskite-type structure was obtained by a liquid mix method. The product was characterized by X-ray diffraction and an orthorhombic structure (Pnma) was found. The particle size was studied by scanning electron microscopy obtaining a mean particle size less than 300 nm.The polarization resistance was studied using two different electrolytes: Y-doped zirconia (YSZ) and Sm-doped ceria (SDC). Chemical reactivity of the LCFN and the electrolytes was studied. Electrochemical Impedance Spectroscopy measurements of LCFN/YSZ/LCFN and LCFN/SDC/LCFN test cells were conducted. These electrochemical experiments were performed at equilibrium from room temperature up to 850{degree sign}C, under zero dc current intensity and under air. The obtained ASR values at 700{degree sign}C for the SDC and YSZ cell tests were 3.23 Ω•cm2 and 85.87 Ω•cm2 , respectively.

Preparation of SDC Interlayer and Influence on Performances of Anode Supported Solid Oxide Fuel Cells

A single cell with a two-layer electrolyte consisting of an yttria stabilized zirconia (YSZ, Y2O3 8 mol%) layer and an Sm-doped ceria (SDC, Sm2O3 20mol%) interlayer has been fabricated on porous YSZ-NiO anode support. The layer of YSZ electrolyte was prepared by modified electrostatic powder coating method and the SDC interlayer by screen-printed method on the green YSZ layer. After co-firing at 1400°C for 5 h, the two-layer film with a dense YSZ film of about 15μm and porous SDC film of about 25μm was fabricated. The performances of as-fabricated single cell using La0.8Sr0.2FeO3 as cathode were tested using H2-3% H2O as fuel and air as oxidant at 800°C. Results indicated that the peak power density of a single cell with SDC interlayer reaches 469 mW/cm2 at 800°C, obviously higher than that of without SDC interlayer, which is about 300 mW/cm2 at 800°C.

Nd 2 − xLa xNiO 4 + δ, a mixed ionic/electronic conductor with interstitial oxygen, as a cathode material

The performance of Nd 2 − x La x NiO 4 + δ as a cathode material for solid oxide fuel cell (SOFC) was evaluated in this paper. Substitution of smaller Nd 3+ ion for La 3+ in La 2NiO 4 + δ increased the retention of mobile interstitial oxygen defects (O i″ ions). The concentration of the O i″ ions in Nd 2NiO 4 + δ was stabilized at δ ≈ 0.12 at 800 °C in air after thermal cycling. As a mixed oxide-ion/electronic conductor (MIEC), Nd 2NiO 4 + δ gave a performance comparable to that of the best perovskite cathode material, SrCo 0.8Fe 0.2O 3 − δ (SCF), for the Sm-doped ceria (SDC) electrolyte-supported SOFC. However, the Nd 2NiO 4 + δ cathode exhibited a higher overpotential with La 0.8Sr 0.2Ga 0.83Mg 0.17O 2.815 (LSGM) as the electrolyte, presumably due to the interdiffusion of La 3+ and Nd 3+ ions across the electrolyte/cathode interface and subsequent formation of ion-blocking phases at the interface. La 1.2Nd 0.8NiO 4 + δ , on the other hand, provided La isoactivity across the LSGM/cathode interface and therefore an improved performance with the LSGM electrolyte. Since Nd 2 − x La x NiO 4 + δ contains neither Sr nor Co, as a cathode, it might be compatible with the electrolytes such as yttria-stabilized zirconia without the need of a buffer layer.

Self-Regeneration Pd-Perovskite Anode for SOFC

A Pd doped perovskite La0.85Sr0.15Cr0.9Ni0.05Pd0.05O3 (LSCNP) was investigated as a candidate for a metal-free anode material of solid oxide fuel cell in comparison with La0.85Sr0.15Cr0.9Ni0.1O3 (LSCN). The performance of anodes of LSCNP and LSCN with and without mixing Sm doped Ceria (SDC) was measured using H2 and dry-CH4 as fuel. The maximum current density of the cell in H2 increased approximately twofold by the doping of Pd for the anode with or without SDC. The rate of the anodic reaction in H2 was enhanced mainly by the catalytic activity of LSCNP and additionally by SDC. When dry-CH4 was used as the fuel, the cell with LSCNP-SDC anode was the only cell which was able to perform power generation. Both the doping of Pd to the perovskite and the mixing of SDC contributed to the ability to operate SOFC in dry CH4. The anode reaction did not occur when SDC was not in the anode, indicating that the supply of oxide ion was the rate determining step. Pd, which is considered to deposit from LSCNP in reducing atmosphere, seemed to be the reaction site of the electrochemical methane oxidation since the reaction rate was low for LSCN-SDC. Although slight indication of carbon deposition was observed, Pd doped perovskite would be a good candidate for metal-free SOFC anode.

Effective Thickness of Ni–Sm-Doped Ceria Cermet Anode for Solid Oxide Fuel Cell

The effective thickness or the active thickness of Ni-Sm-doped ceria cermet anode was investigated by measuring the performance of cells with different anode thickness. The performance of the solid oxide fuel cell (SOFC) increased by increasing the anode thickness. The power density increased as the thickness increased and showed a maximum of 1 W/cm 2 at 2 A/cm 2 for 110 μm anode. This large effective thickness of the electrode was most likely achieved due to the high sintering temperature. Although this structure may not be typical, it indicates an alternative method for the improvement of the anodic performance of SOFCs.

Electrical properties of nanocrystalline Sm-doped ceria ceramics

Electrical properties of nanocrystalline materials are usually different than that of microcrystalline. This phenomenon is not fully understood and therefore it is of continuous interest in the scientific community. In this paper, the results of investigation of nanocrystalline Sm-doped ceria prepared by a net shape technology are presented. The net shape technology is a relatively new ceramic preparation method, which combine powder and polymer precursor methods. The ceramics prepared in this way can be dense and nanocrystalline. Net-shaped prepared Sm-doped ceria was fabricated in the form of bulk ceramics and film on platinum foil. Their electrical properties were investigated and compared with the results obtained from microcrystalline sample.

Ceria coated Ni as anodes for direct utilization of methane in low-temperature solid oxide fuel cells

A new type of anode, a Ni framework coated with Sm-doped ceria (SDC), was developed for direct utilization of methane fuel in low-temperature solid oxide fuel cells (SOFCs) with thin-film SDC electrolytes. The coated SDC was prepared with an ion impregnating method and the electrolyte films were fabricated with a co-pressing and co-firing technique. The impregnating process produced an ideal anode microstructure where nickel particles were effectively connected and uniformly covered with nanosized SDC. This anode microstructure was believed to enlarge the triple-phase boundaries and therefore enhance the anode performance. The cell performance was much higher than that of a conventional fuel cell with a Ni-SDC composite anode. In addition, the performance increased with impregnated SDC loading up to a maximum at 20 mg cm −2, indicating that the coated SDC is the contributing factor for the enhanced fuel cell performance. Power density as high as 571 and 353 mW cm −2 were obtained at 600 °C when humidified hydrogen and methane were used as fuels, respectively. The stability of the cell also increased with the SDC loading. No significant degradation was observed for anodes coated with 20 and 25 mg cm −2 SDC. This verifies that the coated SDC electrodes are very effective in suppressing catalytic carbon formation by blocking methane from approaching the Ni, which is catalytically active towards methane pyrolysis. The high performance of this anode shows high promise in the developing field of direct hydrocarbon SOFCs.

Evaluation of Electrode Performances of Single-Chamber Solid Oxide Fuel Cells

The interfacial resistances of La1-xSrxCo1-yFeyO3-δ (denoted LSCF(10(1-x)/10x/10(1-y)/10y)) cathodes, and the catalytic activities of a Ni-Ce0.85Y0.15O1.925 (Ni-YDC) anode and an LSCF(2/8/8/2) cathode of a single-chamber solid oxide fuel cells (SOFCs) were investigated. LSCF cathodes with high oxide ion conductivities gave low interfacial resistances. LSCF cathodes with suitable thermal expansion coefficients formed favorable interfacial structures with a ceria-based electrolyte. Ni-YDC showed a higher conversion efficiency for CH4 and a lower selectivity for CO2 than LSCF(2/8/8/2). The single-chamber SOFC based on the Sm-doped ceria electrolyte with the Ni-YDC anode and LSCF(2/8/8/2) cathode showed a maximum power density of 186 mW/cm2 at 800°C.

Synthesis and Densification of Nanometric Ce0.8Sm0.2O1.9-δ

AbstractNanometric 20% molar Sm-doped ceria (SDC20) powders were synthesized by tetrametylethylen ammine (TMDA) co-precipitation method. SDC20 was sintered in several conditions to control the final microstructure. Fast firing and conventional sintering were performed. LiNO3was used as an additive to promote liquid phase sintering of ceria at low temperatures (900-1200°C). Powders and dense pellets were analysed using X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), and transmission electron microscopy (TEM). Electrochemical impedance spectroscopy (EIS) measurements were performed on dense pellets in air to estimate the contribution of grain boundary and bulk to the electrical conductivity. Liquid phase sintering produced the densest samples with the highest conductivity.