Performances of LnBaCo2O5+x-Ce0.8Sm0.2O1.9 composite cathodes for intermediate-temperature solid oxide fuel cells

Double-perovskite oxides, LnBaCo₂O_5+x (LnBCO) (Ln = Pr, Nd, Sm, and Gd), are prepared using a solid-state reaction as cathodes for intermediate-temperature solid oxide fuel cells (IT-SOFCs). The performances of LnBCO-Ce_0.8Sm_0.2O_1.9 (SDC) composite cathodes were investigated for IT-SOFCs on La_0.9Sr_0.1Ga_0.8Mg_0.2O_3−δ (LSGM) electrolyte. The thermal expansion coefficient can be effectively reduced in the case of the composite cathodes. No chemical reactions between LnBCO cathodes and SDC electrolyte, and LnBCO and LSGM are found. The electrochemical performances of LnBCO cathodes and LnBCO-SDC composite cathodes decrease with decreasing Ln³⁺ ionic radii, which is closely related to the decrease of the electrical conductivity and fast oxygen diffusion property. The area specific resistances of the LnBCO cathodes and LnBCO-SDC composite cathodes on LSGM electrolyte are all lower than 0.13 Ω cm² and 0.15 Ω cm² at 700 °C, respectively. The maximum power densities of single-cell consisted of LnBCO-SDC composite cathodes, LSGM electrolyte, and Ni-SDC anode achieve 758-608 mW cm⁻² at 800 °C with the change from Ln = Pr to Gd, respectively. These results indicate that LnBCO-SDC composite oxides are candidates as a promising cathode material for IT-SOFCs.     

Characterization of atmospheric plasma-sprayed La0.8Sr0.2Ga0.8Mg0.2O3 electrolyte

La_0.8Sr_0.2Ga_0.8Mg_0.2O₃ (LSGM) deposit in free standing planar shape was prepared by atmospheric plasma spraying (APS) to examine the coating microstructure and electrical conductivity to aim at applying APS LSGM to solid oxide fuel cells (SOFCs). The electrical conductivity of the plasma-sprayed LSGM coating was investigated. The coating microstructure was characterized by X-ray diffraction and scanning electron microscopy. The result showed that a fraction amorphous phase was present in the as-sprayed LSGM deposit, which starts to recrystallize at the temperature of 785 °C. The electrical conductivities of the LSGM with recrystallization treatment are 0.04 and 0.09 S cm⁻¹ at 1000 °C at the directions perpendicular and parallel to the coating surfaces, respectively. The electrical conductivity at perpendicular direction is about one-tenth that of sintered bulk at 1000 °C. This result is due to the lamellar structure feature with the limited interface bonding which dominates the electrical conductivity of APS coatings. The activation energy for ion conduction within APS-deposited LSGM deposit depends on temperature range. The change of activation energy indicates that the ion transportation dominant changes with temperature.     

Combustion synthesis and properties of highly phase-pure perovskite electrolyte Co-doped La0.9Sr0.1Ga0.8Mg0.2O2.85 for IT-SOFCs

The highly phase-pure perovskite electrolyte, La_0.9Sr_0.1Ga_0.8Mg_0.115Co_0.085O_2.85 (LSGMCO), was prepared by means of glycine–nitrate process (GNP) for intermediate-temperature solid oxide fuel cells (IT-SOFCs). The perovskite phase evolution, sintering, electrical conductivity and electrochemical performance of LSGMCO were investigated. The results show that the highly phase-pure perovskite electrolyte LSGMCO can be obtained after calcining at 1150 °C. The sample sintered at 1450 °C for 20 h in air exhibited a better sinterability, and the relative density of LSGMCO was higher than 95%. The stoichiometric indexes of the elements in the sintered sample LSGMCO determined experimentally by EDS were in good agreement with the nominal composition. The electrical conductivities of the sample were 0.094 and 0.124 S· cm⁻¹ at 800 °C and 850 °C in air, respectively. The ionic conduction of the sample was dominant at high temperature with the higher activation energies. While at lower temperature the electron hole conduction was predominated with the lower activation energies. The maximum power densities of the single cell fabricated with LSGMCO electrolyte with Ce_0.8Sm_0.2O_1.9 (SDC) interlayer, SmBaCo₂O_5+x cathode and NiO/SDC anode achieved 643 and 802 mW cm⁻² at 800 °C and 850 °C, respectively.     

La0.7Ca0.3CrO3-Ce0.8Gd0.2O1.9 composites as symmetrical electrodes for solid-oxide fuel cells

La_0.7Ca_0.3CrO₃ (LCC)-Ce_0.8Gd_0.2O_1.9 (GDC) composites have been investigated as symmetrical electrodes for solid-oxide fuel cells (SOFCs) on La_0.9Sr_0.1Ga_0.8Mg_0.2O_3−δ (LSGM) electrolyte, where there is no interlayer between anode and electrolyte. LCC oxide is chemically compatible with GDC and LSGM electrolyte at temperatures up to 1200 °C. The electrical conductivity of the LCC-GDC composites decreases with increasing GDC content. The best electrical conductivities of 18.64 S cm⁻¹ in air and 1.86 S cm⁻¹ in H₂ at 850 °C are achieved for an 80 wt% LCC-20 wt% GDC (LCC-GDC20) composite. The thermal expansion coefficients of the LCC-GDC composites increase with increasing GDC content, and are very close to that of the LSGM electrolyte. A cell with a 0.3 mm thick LSGM electrolyte and LCC-GDC20 symmetrical electrodes displays the highest electrochemical performance. The maximum power density is 573 mW cm⁻² in dry H₂ and 333 mW cm⁻² in humidified commercial city gas containing H₂S at 900 °C, respectively. These results suggest that the LCC-GDC20 composite can potentially serve as an electrode for symmetrical SOFCs operated on H₂ and commercial city gas containing H₂S.     

SmBaCo2O5+x double-perovskite structure cathode material for intermediate-temperature solid-oxide fuel cells

SmBaCo₂O_5+x (SBCO), an oxide with double-perovskite structure, has been developed as a novel cathode material for intermediate-temperature solid-oxide fuel cells (IT-SOFCs). The electrical conductivity of an SBCO sample reaches 815–434 S cm⁻¹ in the temperature range 500–800 °C. XRD results show that an SBCO cathode is chemically compatible with the intermediate-temperature electrolyte materials Sm_0.2Ce_0.8O_1.9 (SDC) and La_0.9Sr_0.1Ga_0.8Mg_0.2O_3−δ (LSGM). The polarization resistances of an SBCO cathode on SDC and LSGM electrolytes are 0.098 and 0.054 Ω cm² at 750 °C, respectively. The maximum power densities of a single cell with an SBCO cathode on SDC and LSGM electrolytes reach 641 and 777 mW cm⁻² at 800 °C, respectively. The results of this study demonstrate that the double-perovskite structure oxide SBCO is a very promising cathode material for use in IT-SOFCs.     

Electrochemical performances of NdBa0.5Sr0.5Co2O5+x as potential cathode material for intermediate-temperature solid oxide fuel cells

Layered perovskite oxide NdBa_0.5Sr_0.5Co₂O_5+x is investigated as a cathode material for intermediate-temperature solid oxide fuel cells. The NBSC cathode is chemically compatible with the electrolyte La_0.9Sr_0.1Ga_0.8Mg_0.2O_3−δ (LSGM) at temperatures below 1000 °C. It is metallic in nature and the maximum and minimum conductivities are 1368 S cm⁻¹ at 100 °C and 389 S cm⁻¹ at 850 °C. The area specific resistance (ASR) value for the NBSC cathode is as low as 0.023 Ω cm² at 850 °C. The electrolyte-supported fuel cell generates good performance with the maximum power density of 904, 774 and 556 mW cm⁻² at 850, 800 and 750 °C, respectively. Preliminary results indicate that NBSC is promising as a cathode for IT-SOFCs.     

Desirable performance of intermediate-temperature solid oxide fuel cell with an anode-supported La0.9Sr0.1Ga0.8Mg0.2O3 − δ electrolyte membrane

An anode-supported La_0.9Sr_0.1Ga_0.8Mg_0.2O_3 − δ (LSGM) electrolyte membrane is successfully fabricated by simple, cost-effective spin coating process. Nano-sized NiO and Ce_0.8Gd_0.2O_3 − α (GDC) powders derived from precipitation and citric-nitrate process, respectively, are used for anode support. The dense and uniform LSGM membrane of ca. 50 μm in thickness is obtained by sintering at relatively low temperature 1300 °C for 5 h. A single cell based on the as-prepared LSGM electrolyte membrane exhibits desirable high cell performance and generates high output power densities of 760 mW cm⁻² at 700 °C and 257 mW cm⁻² at 600 °C, respectively, when operated with humidified hydrogen as the fuel and air as the oxidant. The single cell is characterized by field-emission scanning electron microscope (FESEM), X-ray diffraction (XRD) and electrochemical AC impedance. The results demonstrate that it is feasible to fabricate dense LSGM membrane for solid oxide fuel cell by this simple, cost-effective and efficient process. In addition, optimized anode microstructure significantly reduces polarization resistance (0.025 Ω cm² at 700 °C).     

Physical and electrochemical characterization of Bi2O3-doped scandia stabilized zirconia

Electrolytes based on Sc₂O₃–ZrO₂ exhibit the highest ionic conductivity of zirconia based systems, however, stabilization of the electrochemical properties at operational temperatures, 600–1000 °C, are needed before implementation into SOFCs. Trace additions of Bi₂O₃ are a known sintering aid for zirconia systems. Crystal structures, electrical properties and long-term stability of Bi₂O₃-doped 10ScSZ systems were investigated. The addition of more than 1.0 mol% Bi₂O₃ resulted in suppression of the rhombohedral to cubic phase transformation at 600 °C and cubic phase stabilization at room temperature. The ionic conductivity of 10ScSZ was also improved by Bi₂O₃ additions. A maximum conductivity of 0.034 S cm⁻¹ at 700 °C was observed in 2 mol% Bi₂O₃-doped 10ScSZ sintered at 1300 °C. No phase change was observed in 10ScSZ after annealing at 1000 °C. A certain amount of monoclinic phase, and dramatic conductivity decrease, were observed in Bi₂O₃-doped samples sintered below 1200 °C after annealing. However, 10ScSZ and 2 mol% Bi₂O₃-doped 10ScSZ sintered at 1300 °C show no significant conductivity degradation with annealing. Samples with more than 1 mol% Bi₂O₃ and sintered above 1300 °C resulted in good ionic conductivity and stability.     

BaCo0.7Fe0.2Nb0.1O3−δ as cathode material for intermediate temperature solid oxide fuel cells

BaCo_0.7Fe_0.2Nb_0.1O_3−δ (BCFN) has been synthesized and characterized as cathode material for intermediate temperature solid oxide fuel cells (IT-SOFCs) using La_0.8Sr_0.2Ga_0.83Mg_0.17O_3−δ (LSGM) electrolyte. X-ray diffraction results show that pure cubic BCFN perovskite phase can be obtained at 950 °C through solid state reactions of BaCO₃, Co₃O₄, Fe₂O₃ and Nb₂O₅. The electrical conductivity of BCFN increases with the increase in oxygen partial pressure, indicating that BCFN is a p-type semiconductor. The polarization resistance of the BCFN cathode with LSGM electrolyte is only 0.06 Ω cm² at 750 °C in air under open-circuit conditions. The overpotential at a current density of 1 A cm⁻² in oxygen was only about 0.04 V at 750 °C. Peak power densities of 550, 770 and 980 mW cm⁻² have been achieved on LSGM-electrolyte supported single cells with the configuration of Ni-Gd_0.1Ce_0.9O_1.95|La_0.4Ce_0.6O₂|LSGM|BCFN at 700, 750 and 800 °C, respectively. These results indicate that BCFN is a very promising cathode candidate for IT-SOFCs with LSGM electrolyte.     

Preparation and electrochemical performance of Pr2Ni0.6Cu0.4O4 cathode materials for intermediate-temperature solid oxide fuel cells

Cathode material Pr₂Ni_0.6Cu_0.4O₄ (PNCO) for intermediate-temperature solid oxide fuel cells (IT-SOFCs) is synthesized by a glycine-nitrate process using Pr₆O₁₁, NiO, and CuO powders as raw materials. X-ray diffraction analysis reveals that nanosized Pr₂Ni_0.6Cu_0.4O₄ powders with K₂NiF₄-type structure can be obtained from calcining the precursors at 1000 °C for 3 h. Scanning electron microscopy shows that the sintered PNCO samples have porous microstructure with a porosity of more than 30% and grain size smaller than 2 μm. A maximum conductivity of 130 S cm⁻¹ is obtained from the PNCO samples sintered at 1050 °C. A single fuel cell based on the PNCO cathode with 30 μm Sm_0.2Ce_0.8O_1.9 (SCO) electrolyte film and a 1 mm NiO-SCO anode support is constructed. The ohmic resistance of the single Ni-SCO/SCO/PNCO cell is 0.08 Ω cm² and the area specific resistance (ASR) value is 0.19 Ω cm² at 800 °C. Cell performance was also tested using humidified hydrogen (3% H₂O) as fuel and air as oxidant. The single cell shows an open circuit voltage of 0.82 V and 0.75 V at 700 °C and 800 °C, respectively. Maximum power density is 238 mW cm⁻² and 308 mW cm⁻² at 700 °C and 800 °C, respectively. The preliminary tests have shown that Pr₂Ni_1−xCu_xO₄materials can be a good candidate for cathode materials of IT-SOFCs.     

PrBa0.5Sr0.5Co2O5+x as cathode material based on LSGM and GDC electrolyte for intermediate-temperature solid oxide fuel cells

PrBa_0.5Sr_0.5Co₂O_5+x (PBSC) oxides have been evaluated as cathode materials for intermediate-temperature solid oxide fuel cells (IT-SOFCs) with Ce_0.9Gd_0.1O_1.95 (GDC) and La_0.9Sr_0.1Ga_0.8Mg_0.2O_3−δ (LSGM) as electrolytes. XRD results show that PBSC cathode is chemically compatible with the intermediate-temperature electrolyte materials GDC and LSGM. The maximum electrical conductivity is 1522 S cm⁻¹ at 100 °C and its value is higher than 581 S cm⁻¹ over the whole temperature range investigated. Microstructures show that the contact between PBSC and LSGM is better than that between PBSC and GDC. The area-specific resistances (ASRs) of PBSC cathode on GDC and LSGM electrolytes are 0.048 and 0.027 Ωcm² at 800 °C, respectively. The electrolyte-supported (thickness of electrolyte is 300 μm) fuel cells generate good performance with the maximum power densities of 617 mW cm⁻² on GDC electrolyte and 1021 mW cm⁻² on LSGM electrolyte at 800 °C. All results demonstrate that PBSC oxide is a very promising cathode material for application in IT-SOFCs and this cathode based on LSGM electrolyte obtained better performance than on GDC electrolyte.     

Effect of Co doping on the properties of Sr0.8Ce0.2MnO3−δ cathode for intermediate-temperature solid-oxide fuel cells

The effect of the Co doping on the structure, electrical conductivity and electrochemical properties of Sr_0.8Ce_0.2MnO_3−δ was investigated. The Co doping decreased the sintering temperature by about 100 °C and cubic structure was synthesized for Sr_0.8Ce_0.2Mn_0.8Co_0.2O_3−δ. The electrical conductivity of Sr_0.8Ce_0.2Mn_0.8Co_0.2O_3−δ reached 102 S cm⁻¹ at 700 °C, which was sufficient to provide low ohmic losses at the cathode. In comparison with Sr_0.8Ce_0.2MnO_3−δ, the area-specific resistance of Sr_0.8Ce_0.2Mn_0.8Co_0.2O_3−δ was 0.10 Ω cm² at 750 °C, which was about 20 times lower than that of Sr_0.8Ce_0.2MnO_3−δ. While the exchange current density i₀ of Sr_0.8Ce_0.2Mn_0.8Co_0.2O_3−δ was 0.49 A cm⁻² at 800 °C, that for Sr_0.8Ce_0.2MnO_3−δ was 0.11 A cm⁻². The results show that the Sr_0.8Ce_0.2Mn_0.8Co_0.2O_3−δ cathode had high catalytic activity for oxygen reduction reaction in the temperature range of 700–800 °C.     

Double-perovskites YBaCo2−xFexO5+δ cathodes for intermediate-temperature solid oxide fuel cells

Double-perovskites YBaCo_2−xFe_xO_5+δ (YBCF, x = 0.0, 0.2, 0.4 and 0.6) are synthesized with a solid-state reaction and are assessed as potential cathode materials for utilization in intermediate-temperature solid oxide fuel cells (IT-SOFCs) on the La_0.9Sr_0.1Ga_0.8Mg_0.115Co_0.085O_2.85 (LSGMC) electrolyte. The YBCF materials exhibit chemical compatibility with the LSGMC electrolyte up to a temperature of 950 °C. The conductivity of the YBCF samples decreases with increasing Fe content, and the maximum conductivity of YBCF is 315 S cm⁻¹ at 325 °C for the x = 0.0 sample. A semiconductor-metal transition is observed at about 300-400 °C. The thermal expansion coefficient of the YBCF samples increases from 16.3 to 18.0 × 10⁻⁶ K⁻¹ in air at temperatures between 30 and 900 °C with increase in Fe content. The area-specific resistances of YBCF cathodes at x = 0.0, 0.2 and 0.4 on the LSGMC electrolyte are 0.11, 0.13 and 0.15 Ω cm² at a temperature of 700 °C, respectively. The maximum power densities of the single cells fabricated with the LSGMC electrolyte, Ce_0.8Sm_0.2O_1.9 (SDC) interlayer, NiO/SDC anode and YBCF cathodes at x = 0.0, 0.2 and 0.4 reach 873, 768 and 706 mW cm⁻², respectively. This study suggests that the double-perovskites YBCF (0 ≤ x ≤ 0.4) can be potential candidates for utilization as IT-SOFC cathodes.     

Electrochemical performance of (Ba0.5Sr0.5)0.9Sm0.1Co0.8Fe0.2O3−δ as an intermediate temperature solid oxide fuel cell cathode

This study presents the electrochemical performance of (Ba_0.5Sr_0.5)_0.9Sm_0.1Co_0.8Fe_0.2O_3−δ (BSSCF) as a cathode material for intermediate temperature solid oxide fuel cells (IT-SOFC). AC-impedance analyses were carried on an electrolyte supported BSSCF/Sm_0.2Ce_0.8O_1.9 (SDC)/Ag half-cell and a Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3−δ (BSCF)/SDC/Ag half-cell. In contrast to the BSCF cathode half-cell, the total resistance of the BSSCF cathode half-cell was lower, e.g., at 550 °C; the values for the BSSCF and BSCF were 1.54 and 2.33 Ω cm², respectively. The cell performance measurements were conducted on a Ni-SDC anode supported single cell using a SDC thin film as electrolyte, and BSSCF layer as cathode. The maximum power densities were 681 mW cm⁻² at 600 °C and 820 mW cm⁻² at 650 °C.     

Sr2Fe4/3Mo2/3O6 as anodes for solid oxide fuel cells

Sr₂Fe_4/3Mo_2/3O₆ has been synthesized by a combustion method in air. It shows a single cubic perovskite structure after being reduced in wet H₂ at 800 °C and demonstrates a metallic conducting behavior in reducing atmospheres at mediate temperatures. Its conductivity value at 800 °C in wet H₂ (3% H₂O) is about 16 S cm⁻¹. This material exhibits remarkable electrochemical activity and stability in H₂. Without a ceria interlayer, maximum power density (P_max) of 547 mW cm⁻² is achieved at 800 °C with wet H₂ (3% H₂O) as fuel and ambient air as oxidant in the single cell with the configuration of Sr₂Fe_4/3Mo_2/3O₆|La_0.8Sr_0.2Ga_0.83Mg_0.17O₃ (LSGM)| La_0.6Sr_0.4Co_0.2Fe_0.8O₃ (LSCF). The P_max even increases to 595 mW cm⁻² when the cell is operated at a constant current load at 800 °C for additional 15 h. This anode material also shows carbon resistance and sulfur tolerance. The P_max is about 130 mW cm⁻² in wet CH₄ (3% H₂O) and 472 mW cm⁻² in H₂ with 100 ppm H₂S. The cell performance can be effectively recovered after changing the fuel gas back to H₂.     

Electrochemical behavior of Ba0.5Sr0.5Co0.2−xZnxFe0.8O3−δ (x = 0-0.2) perovskite oxides for the cathode of solid oxide fuel cells

Zinc-doped barium strontium cobalt ferrite (Ba_0.5Sr_0.5Co_0.2−xZn_xFe_0.8O_3−δ (BSCZF), x = 0, 0.05, 0.1, 0.15, 0.2) powders with various proportions of zinc were prepared using the ethylenediamine tetraacetic acid (EDTA)-citrate method with repeated ball-milling and calcining. They were then evaluated as cathode materials for solid oxide fuel cells at intermediate temperatures (IT-SOFCs) using XRD, H₂-TPR, SEM, and electrochemical tests. By varying the zinc doping (x) from zero to 0.2 (as a substitution for cobalt which ranged from zero to 100%), it was found that the lowest doping of 0.05 (BSCZF05) resulted in the highest electrical conductivity of 30.7 S cm⁻¹ at 500 °C. The polarization resistances of BSCZF05 sintered at 950 °C were 0.15 Ω cm², 0.28 Ω cm² and 0.59 Ω cm² at 700 °C, 650 °C and 600 °C, respectively. The resistance decreased further by about 30% when Sm_0.2Ce_0.8O_2−δ (SDC) electrolyte particles were incorporated and the sintering temperature was increased to 1000 °C. Compared to BSCF without zinc, BSCZF experienced the lowest decrease in electrochemical properties when the sintering temperature was increased from 950 °C to 1000 °C. This decrease was due to an increase in thermal stability and a minimization in the loss of some cobalt cations without a decrease in the electrical conductivity. Using a composite cathode of BSCZF05 and 30 wt.% of SDC, button cells composed of an Ni-SDC support with a 30 μm dense SDC membrane exhibited a maximum power density of 605 mW cm⁻² at 700 °C.     

Sr2CoMoO6 anode for solid oxide fuel cell running on H2 and CH4 fuels

The double perovskite Sr₂CoMoO_6−δ was investigated as a candidate anode for a solid oxide fuel cell (SOFC). Thermogravimetric analysis (TGA) and powder X-ray diffraction (XRD) showed that the cation array is retained to 800 °C in H₂ atmosphere with the introduction of a limited concentration of oxide-ion vacancies. Stoichiometric Sr₂CoMoO₆ has an antiferromagnetic Néel temperature T_N ≈ 37 K, but after reduction in H₂ at 800 °C for 10 h, long-range magnetic order appears to set in above 300 K. In H₂, the electronic conductivity increases sharply with temperature in the interval 400 °C < T < 500 °C due to the onset of a loss of oxygen to make Sr₂CoMoO_6−δ a good mixed oxide-ion/electronic conductor (MIEC). With a 300-μm-thick La_0.8Sr_0.12Ga_0.83Mg_0.17O_2.815 (LSGM) as oxide-ion electrolyte and SrCo_0.8Fe_0.2O_3−δ as the cathode, the Sr₂CoMoO_6−δ anode gave a maximum power density of 1017 mW cm⁻² in H₂ and 634 mW cm⁻² in wet CH₄. A degradation of power in CH₄ was observed, which could be attributed to coke build up observed by energy dispersive spectroscopy (EDS).     

Performance of strontium- and magnesium-doped lanthanum gallate electrolyte with lanthanum-doped ceria as a buffer layer for IT-SOFCs

La_0.8Sr_0.2Ga_0.8Mg_0.2O_2.8 (LSGM8080) powder, showing the highest electrical conductivity among LSGMs of various compositions, is synthesized using the glycine nitrate process (GNP) and used as the electrolyte for an intermediate-temperature solid oxide fuel cell (IT-SOFC). The LDC (Ce_0.55La_0.45O_1.775) powder is synthesized by a solid-state reaction and employed as the material for a buffer layer to prevent the reaction between the anode and electrolyte materials. The LDC also serves as the skeleton material for the anode. An anode-supported single cell with an active area of 1 cm² is constructed for performance evaluation. A single-cell test is performed at 750 and 800 °C. The maximum power density of the cell 459 and 664 mW cm⁻² at 750 and 800 °C, respectively.     

Synthesis and sintering of Gd-doped CeO2 electrolytes with and without 1 at.% CuO dopping for solid oxide fuel cell applications

Nano-sized Ce_0.8Gd_0.2O_2−δ and Ce_0.79Gd_0.2Cu_0.01O_2−δ electrolyte powders were synthesized by the polyvinyl alcohol assisted combustion method, and then characterized by powder characteristics, sintering behaviors and electrical properties. The results demonstrate that the as-synthesized Ce_0.8Gd_0.2O_2−δ and Ce_0.79Gd_0.2Cu_0.01O_2−δ possessed similar powder characteristics, including cubic fluorite crystalline structure, porous foamy morphology and agglomerated secondary particles composed of gas cavities and primary nano crystals. Nevertheless, after ball-milling these two powders exhibited quite different sintering abilities. A significant reduction of about 400 °C in densification temperature of Ce_0.79Gd_0.2Cu_0.01O_2−δ was obtained when compared with Ce_0.8Gd_0.2O_2−δ. The Ce_0.79Gd_0.2Cu_0.01O_2−δ pellets sintered at 1000 °C and the Ce_0.8Gd_0.2O_2−δ sintered at 1400 °C exhibited relative densities of 96.33% and 95.7%, respectively. The sintering of Ce_0.79Gd_0.2Cu_0.01O_2−δ was dominated by the liquid phase process, followed by the evaporation-condensation process, Moreover, Ce_0.79Gd_0.2Cu_0.01O_2−δ shows much higher conductivity of 0.026 S cm⁻¹ than Ce_0.8Gd_0.2O_2−δ (0.0065 S cm⁻¹) at a testing temperature of 600 °C.     

High performance metal-supported intermediate temperature solid oxide fuel cells fabricated by atmospheric plasma spraying

The LSGM(La_0.8Sr_0.2Ga_0.8Mg_0.2O₃) electrolyte based intermediate temperature solid oxide fuel cells (ITSOFCs) supported by porous nickel substrates with different permeabilities are prepared by plasma spray technology for performance studies. The cell having a porous nickel substrate with a permeability of 3.4 Darcy, an LSCM(La_0.75Sr_0.25Cr_0.5Mn_0.5O₃) interlayer on the nickel substrate, a nano-structured LDC(Ce_0.55La_0.45O₂)/Ni anode functional layer, an LDC interlayer, an LSGM/LSCF(La_0.58Sr_0.4Co_0.2Fe_0.8O₃) cathode interlayer and an LSCF cathode current collector layer shows remarkable electric output power densities such as 1270 mW cm⁻² (800 °C), 978 mW cm⁻² (750 °C) and 702 mW cm⁻² (700 °C) at 0.6 V cell voltage under 335 ml min⁻¹ H₂ and 670 ml min⁻¹ air flow rates. SEM, TEM, EDX, AC impedance, voltage and power data with related analyses are presented here to support this high performance. The durability test of the cell with the best power performance shows a degradation rate of about 3% kh⁻¹ at the test conditions of 400 mA cm⁻² constant current density and 700 °C. Results demonstrate the success of APS technology for fabricating high performance metal-supported and LSGM based ITSOFCs.