Study on Sm1.8Ce0.2CuO4-Ce0.9Gd0.1O1.95 composite cathode materials for intermediate temperature solid oxide fuel cell

Sm_1.8Ce_0.2CuO₄-xCe_0.9Gd_0.1O_1.95 (SCC-xCGO, x = 0-12 vol.%) composite cathodes supported on Ce_0.9Gd_0.1O_1.95 (CGO) electrolyte are studied for applications in IT-SOFCs. Results show that Sm_1.8Ce_0.2CuO₄ material is chemically compatible with Ce_0.9Gd_0.1O_1.95 at 1000 °C. The composite electrode exhibits optimum microstructure and forms good contact with the electrolyte after sintering at 1000 °C for 4 h. The polarization resistance (R_p) reduces to the minimum value of 0.17 Ω cm² at 750 °C in air for SCC-CGO06 composite cathode. The relationship between R_p and oxygen partial pressure indicates that the reaction rate-limiting step is the surface diffusion of the dissociative adsorbed oxygen on the composite cathode.     

High sintering activity Cu-Gd co-doped CeO2 electrolyte for solid oxide fuel cells

Nano-sized Ce_0.79Gd_0.2Cu_0.01O_2−δ electrolyte powder was synthesized by the polyvinyl alcohol assisted combustion method, and then characterized by crystalline structure, powder morphology, sintering micro-structure and electrical properties. The results demonstrate that the as-synthesized Ce_0.79Gd_0.2Cu_0.01O_2−δ was well crystalline with cubic fluorite structure, and exhibited a porous foamy morphology composed of gas cavities and fine crystals ranging from 30 to 50 nm. After sintering at 1100 °C, the as-prepared pellets exhibited a dense and moderate-grained micro-structure with 95.54% relative density, suggesting that the synthesized Ce_0.79Gd_0.2Cu_0.01O_2−δ powder had high sintering activity. The powders made by this method are expected to offer potential application in intermediate-to-low temperature solid-oxide fuel cells, due to its very low densification sintering temperature (1100 °C), as well as high conductivity of 0.026 S cm⁻¹ at 600 °C and good mechanical performance with three-point flexural strength value of 148.15 ± 2.42 MPa.     

Electrical properties of Mg-doped Gd0.1Ce0.9O1.95 under different sintering conditions

Ce_0.9Gd_0.1O_1.95 with various Mg doping contents was synthesized by citric acid-nitrate low temperature combustion process and sintered under different conditions. The crystal structures, microstructures and electrical properties were characterized by X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM) and ac impedance spectroscopy. Low solubility of Mg²⁺ in Ce_0.9Gd_0.1O_1.95 lattice was evidenced by XRD and FESEM micrographs. The samples sintered at 1300 °C exhibited the higher total conductivity than those sintered at 1100 and 1500 °C, with the maximum value of 1.48 × 10⁻² S cm⁻¹ (measured at 600 °C) at the Mg doping content of 6 mol%, corresponding to the minimum total activation energy (E_tol) of 0.84 eV (150–400 °C). The effect of Mg doping on the electrical conductivity was significant particularly at higher sintering temperatures. At the sintering temperature of 1500 °C, the addition of Mg (10 mol%) enhanced the grain boundary conductivity by over 10² times comparing with that of undoped Ce_0.9Gd_0.1O_1.95, which may be explained by the optimization of space charge layer due to the segregation of Mg²⁺ to the grain boundaries.     

Co-doped Sr2FeNbO6 as cathode materials for intermediate-temperature solid oxide fuel cells

Sr₂Fe_1−xCo_xNbO₆ (0.1 ≤ x ≤ 0.9) (SFCN) oxides with perovskite structure have been developed as the cathode materials for intermediate-temperature solid oxide fuel cells (IT-SOFCs). These materials are synthesized via solid-state reaction and characterized by XRD, SEM, electrical conductivity, AC impedance spectroscopy and DC polarization measurements. The reactivity tests show that the Sr₂Fe_1−xCo_xNbO₆ electrodes are chemically compatible with the Zr_0.85Y_0.15O_1.925 (YSZ) and Ce_1.9Gd_0.1O_1.95 (CGO) electrolytes at 1200 °C, and the electrode forms a good contact with the electrolyte after sintering at 1200 °C for 12 h. The total electrical conductivity that has a considerable effect on the electrode properties is determined in a temperature range from 200 °C to 800 °C. The highest conductivity of 5.7 S cm⁻¹ is found for Sr₂Fe_0.1Co_0.9NbO₆ at 800 °C in air. The electrochemical performances of these cathode materials are studied using impedance spectroscopy at various temperatures and oxygen partial pressures. Two different kinds of reaction rate-limiting steps exist on the Sr₂Fe_0.1Co_0.9NbO₆ electrode, depending on the temperature. The Sr₂Fe_0.1Co_0.9NbO₆ electrode on CGO electrolyte exhibits a polarization resistance of 0.74 Ω cm² at 750 °C in air, which indicates that the Sr₂Fe_0.1Co_0.9NbO₆ electrode is a promising cathode material for IT-SOFCs.     

Preparation and characterization of Ce1−x(Gd0.5Pr0.5)xO2 electrolyte for IT-SOFCs

The Ce_1−x(Gd_0.5Pr_0.5)_xO₂ (x = 0–0.24) compositions were synthesized through the sol–gel process followed by low temperature combustion. X-ray diffraction data analysis showed that all the samples exhibit a cubic structure with single phase. The lattice parameter was calculated by rietveld refinement of XRD patterns. Dense ceramics were prepared by sintering the pellets at 1300 °C. The relative density of the samples was over 98%. The surface morphology was studied by Scanning electron microscopy (SEM). Chemical composition was analyzed by Energy dispersive spectroscopy (EDX). A.C. impedance spectroscopy measurements were carried out to study the grain, grain boundary and total ionic conductivity of co-doped ceria samples in the temperature range 150–700 °C. The Ce_0.84(Gd_0.5Pr_0.5)_0.16O₂ composition showed highest grain ionic conductivity i.e., 1.059 × 10⁻² S/cm at 500 °C which is 11.5% higher than the Ce_0.9Gd_0.1O₂ (with an activation energy 0.62 eV). At intermediate temperatures, the Ce_1−x(Gd_0.5Pr_0.5)_xO₂ materials were found to be ionic in nature.     

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.     

Fabrication and characterization of a co-fired La0.6Sr0.4Co0.2Fe0.8O3−δ cathode-supported Ce0.9Gd0.1O1.95 thin-film for IT-SOFCs

A dense membrane of Ce_0.9Gd_0.1O_1.95 on a porous cathode based on a mixed conducting La_0.6Sr_0.4Co_0.2Fe_0.8O_3−δ was fabricated via a slurry coating/co-firing process. With the purpose of matching of shrinkage between the support cathode and the supported membrane, nano-Ce_0.9Gd_0.1O_1.95 powder with specific surface area of 30 m² g⁻¹ was synthesized by a newly devised coprecipitation to make the low-temperature sinterable electrolyte, whereas 39 m² g⁻¹ nano-Ce_0.9Gd_0.1O_1.95 prepared from citrate method was added to the cathode to favor the shrinkage for the La_0.6Sr_0.4Co_0.2Fe_0.8O_3−δ. Bi-layers consisting of <20 μm dense ceria film on 2 mm thick porous cathode were successfully fabricated at 1200 °C. This was followed by co-firing with NiO–Ce_0.9Gd_0.1O_1.95 at 1100 °C to form a thin, porous, and well-adherent anode. The laboratory-sized cathode-supported cell was shown to operate below 600 °C, and the maximum power density obtained was 35 mW cm⁻² at 550 °C, 60 mW cm⁻² at 600 °C.     

Improved electrochemical performance and thermal compatibility of Fe- and Cu-doped SmBaCo2O5+δ-Ce0.9Gd0.1O1.95 composite cathode for intermediate-temperature solid oxide fuel cells

Fe- and Cu-doped SmBaCo₂O_5+δ (FC-SBCO)-Ce_0.9Gd_0.1O_1.95 (CGO) composites with various CGO contents (0-40 wt.%) are investigated as new cathode materials for intermediate-temperature solid oxide fuel cells (IT-SOFCs) based on a Ce_0.9Gd_0.1O_1.95 electrolyte. The effect of CGO incorporation on the thermal expansion coefficient (TEC), electrochemical properties and thermal stability of the FC-SBCO-CGO composites is investigated. A composite cathode of 30 wt.% CGO-70 wt.% FC-SBCO (CS30-70) coated on a Ce_0.9Gd_0.1O_1.95 electrolyte shows the lowest area specific resistance (ASR), i.e., 0.049 Ω cm² at 700 °C. The TEC of the CS30-70 cathode is 14.1 × 10⁻⁶ °C⁻¹ up to 900 °C, which is a lower value than that of the FC-SBCO (16.6 × 10⁻⁶ °C⁻¹) counterpart. Long-term thermal stability and thermal cycle tests of the CS30-70 cathode are performed. Stable ARS values are observed during both type of test. An electrolyte-supported (300-μm thick) single-cell configuration of CS30-70/CGO/Ni-CGO delivers a maximum power density of 535 mW cm⁻² at 700 °C. The unique composite composition of CS30-70 demonstrates improved electrochemical performance and good thermal stability for IT-SOFCs.     

Structural,morphological and electrical properties of Gd0.1Ce0.9O1.95 prepared by a citrate complexation method

A variant of the sol–gel technique known as cation complexation is used to prepare a nanocrystalline Gd_0.1Ce_0.9O_1.95 (GDC) solid solution. A range of techniques including thermal analysis (TGA/DTA), X-ray diffraction, specific surface area determination (BET) and electron microscopy (SEM and TEM) are employed to characterise the GDC powders. GDC calcined at 500 °C is found to have an average crystallite size of 11 nm. Specific surface areas are found to be 29.7 m² g⁻¹ for the as-calcined powder and 57.5 m² g⁻¹ after ball milling at 400 rpm. Dense ceramic pellets are prepared from unmilled and ball-milled GDC powders employing different thermal treatments. Their electrical properties are studied by impedance spectroscopy. Those samples sintered at 1300 °C for 30 h (starting from ball-milled powders) exhibit the highest density (96% of theoretical density) and the highest total ionic conductivity (1.91 × 10⁻² S cm⁻¹ at 600 °C).     

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.     

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.     

Grain boundary conductivity of high purity neodymium-doped ceria nanosystem with and without the doping of molybdenum oxide

Solid solutions of Ce_1−xNd_xO_2−x/2 (0.05 ≤ x ≤ 0.2) and (Ce_1−xNd_x)_0.95Mo_0.05O_2−δ (0.05 ≤ x ≤ 0.2) have been synthesized by a modified sol–gel method. Both materials have very low content of SiO₂ (∼27 ppm). Their structures and ionic conductivities were characterized by X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM) and electrochemical impedance spectroscopy (EIS). The XRD patterns indicate that these materials are single phases with a cubic fluorite structure. The powders calcined at 300 °C with a crystal size of 5.7 nm have good sinterability, and the relative density could reach above 96% after being sintered at 1450 °C. With the addition of MoO₃, the sintering temperature could be decreased to 1250 °C. Impedance spectroscopy measurement in the temperature range of 250–800 °C indicates that a sharp increase of conductivity is observed when a small amount of Nd₂O₃ is added into ceria, of which Ce_0.85Nd_0.15O_1.925 (15NDC) shows the highest conductivity. With the addition of a small amount of MoO₃, the grain boundary conductivity of 15NDC at 600 °C increases from 2.56 S m⁻¹ to 5.62 S m⁻¹.     

BaZr0.1Ce0.7Y0.1Yb0.1O3−δ electrolyte-based solid oxide fuel cells with cobalt-free PrBaFe2O5+δ layered perovskite cathode

A new anode-supported SOFC material system Ni-BZCYYb|BZCYYb|PBFO is investigated, in which a cobalt-free layered perovskite oxide, PrBaFe₂O_5+δ (PBFO), is synthesized and employed as a novel cathode while the synthesized BZCYYb is used as an electrolyte. The cell is fabricated by a simple dry-pressing/co-sintering process. The cell is tested and characterized under intermediate temperature range from 600 to 700 °C with humified H₂ (∼3% H₂O) as fuel, ambient air as oxidant. The results show that the open-circuit potential of 1.006 V and maximal power density of 452 mW cm⁻² are achieved at 700 °C. The polarization resistance of the electrodes is 0.18 Ω cm² at 700 °C. Compared to BaZr_0.1Ce_0.7Y_0.1O_3−δ, the conductivity of co-doped barium zirconate-cerate BZCYYb is significantly improved. The ohmic resistance of single cell is 0.37 Ω cm² at 700 °C. The results indicate that the developed Ni-BZCYYb|BZCYYb|PBFO cell is a promising functional material system for SOFCs.     

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.     

Preparation and property-performance relationships in samarium-doped ceria nanopowders for solid oxide fuel cell electrolytes

In a systematic study, Samarium doped ceria (SDC) nanopowders, Sm_xCe_1−xO_2−x/2 (x = 0.1, 0.2 or 0.3), were prepared by a low temperature citrate complexation route. The synthesis and crystallisation of the SDC powders were followed by thermochemical techniques (TGA/DTA), X-ray diffraction, elemental analysis, specific surface area determination (BET) and electron microscopy (SEM and TEM). Mean crystallite sizes were found to be around 10 nm for all compositions calcined at 500 °C. Dense electrolyte bodies were prepared at 1300 °C, 1400 °C and 1450 °C using two sintering times, 4 h or 6 h. Densities of 91-97% of theoretical were obtained, with a marked improvement in density on going from 1300 °C to higher sintering temperatures. Grain size analysis was conducted using SEM. Grain size distributions were related to %Sm and sintering conditions. Impedance spectroscopy was used to determine the total, bulk and grain boundary conductivities, the related activation energies and enthalpies of defect association and ion migration. Sintering at 1400 °C/6 h or 1450 °C/4 h gave superior grain structure and conductivity, with oversintering occurring after more severe treatments. At 600 °C the highest total ionic conductivity was 1.81 × 10⁻² S cm⁻¹ for Sm_0.2Ce_0.8O_1.9. The relationships between chemical composition, sintering parameters, grain structure and electrochemical performance are discussed.     

Low-temperature sintering and electrical properties of strontium- and magnesium-doped lanthanum gallate with V2O5 additive

The effects of a V₂O₅ additive on the low-temperature sintering and ionic conductivity of strontium- and magnesium-doped lanthanum gallate (LSGM: La_0.8Sr_0.2Ga_0.8Mg_0.2O_2.8) are studied. The LSGM powders prepared by the glycine nitrate method are mixed with 0.5-2 at.% of VO_5/2 and then sintered at 1100-1400 °C in air for 4 h. The apparent density and phase purity of the LSGM specimens are increased with increasing sintering temperature and VO_5/2 concentration due to the enhanced sintering and mass transfer via the intergranular liquid phase. The 1 at.% VO_5/2-doped LSGM specimen sintered at 1300 °C exhibits a high oxide ion conductivity of ∼0.027 S cm⁻¹ at 700 °C over a wide range of oxygen partial pressure (PO₂=10⁻²⁷−1 atm), thereby demonstrating its potential as a useful electrolyte for anode-supported solid oxide fuel cells (SOFCs) without the requirement for any buffer layer between the electrolyte and anode.     

High performance composite interconnect La0.7Ca0.3CrO3/20 mol% ReO1.5 doped CeO2 (Re = Sm,Gd, Y) for solid oxide fuel cells

This paper reports and discusses composite interconnect materials that were modified from La_0.7Ca_0.3CrO_3−δ (LCC) by addition of Re doped CeO₂ (Re = Sm, Gd, Y) for improved conductivity at relative low temperatures. It is found that the addition of small amounts of RDC (ReO_1.5 doped CeO₂) into LCC dramatically increased the electrical conductivity. For the best system studied, LCC + 5 wt% SDC (Sm_0.2Ce_0.8O_1.9), LCC + 3 wt% GDC (Gd_0.2Ce_0.8O_1.9) and LCC + 3 wt% YDC (Y_0.2Ce_0.8O_1.9), the electrical conductivities reached 687.8, 124.6 and 104.8 S cm⁻¹ at 800 °C in air, respectively. The electrical conductivities of the specimens, LCC + 3 wt% SDC, LCC + 1 wt% GDC and LCC + 2 wt% YDC in H₂ at 800 °C were 7.1, 3.8 and 5.9 S cm⁻¹, respectively. With the increase of RDC content, the relative density increased, indicating that RDC served as an effective sintering aid in enhancing the sinterability of the powders. The average coefficient of thermal expansion (CTE) at 30–1000 °C in air increased with the increase of the RDC content. The oxygen permeation measurements indicated a negligible oxygen ionic conduction, indicating that the efficiency loss of a solid oxide fuel cell by permeation is negligible for the general cell design using LCC + RDC as interconnect. Therefore, the composite materials La_0.7Ca_0.3CrO₃/20 mol% ReO_1.5 doped CeO₂ are very promising interconnecting ceramics for solid oxide fuel cells (SOFCs).     

Doping effects on complex perovskite Ba3Ca1.18Nb1.82O9−δ intermediate temperature proton conductor

In this work, the effects of Ce doping on the Ca and Nb ions in complex perovskite Ba₃Ca_1.18Nb_1.82O_9−δ (BCN18) proton conductor have been evaluated. It has been found that cerium ions can be doped into both the Ca and Nb sites to form a single-phase complex perovskite structure when the sintering temperature is 1550 °C. Ce ions substituted with Nb ions enhances the electrical conductivity, especially the grain boundary conductivity. The highest conductivity has been obtained for a composition of Ba₃Ca_1.18Nb_1.62Ce_0.2O_9−δ, possessing a conductivity of 2.69 × 10⁻³ S cm⁻¹ at 550 °C in wet H₂, a 78% enhancement compared with BCN18 (1.51 × 10⁻³ S cm⁻¹). The chemical stability tests show that Ce-doped BCN18 samples remain single phase after treated either in boiling water for 7 h or in pure CO₂ for 4 h at 700 °C. This work has demonstrated a new direction in developing intermediate temperature proton conducting materials that possess both high conductivity and good stability.     

Improved electrical conductivity of Ce0.9Gd0.1O1.95 and Ce0.9Sm0.1O1.95 by co-doping

Solid electrolytes are the most important and indispensable part of a solid oxide fuel cell (SOFC) where hydrogen is used as one of the fuels to obtain electricity. Ce_0.9Gd_0.1O_1.95 and Ce_0.9Sm_0.1O_1.95 were chosen to be the base electrolytes. The effects of MgO and Nd₂O₃ as co-dopants on the electrical conductivity were investigated, respectively. For 4 mol% Mg-doped Ce_0.9Gd_0.1O_1.95 or Ce_0.9Sm_0.1O_1.95, MgO phases were detected by FESEM micrographs, which showed a very low solubility of Mg²⁺ in ceria lattice. The existence of MgO phases was observed to have negligible effect on the grain conductivity, but improve the grain boundary conductivity measured by ac impedance spectroscopy. However, when Nd₂O₃ was used as a co-dopant, XRD patterns and FESEM both indicated a pure cubic phase. Ce_0.9Gd_0.05Nd_0.05O_1.95 and Ce_0.9Sm_0.05Nd_0.05O_1.95 were found to exhibit higher grain conductivity, comparing with single-doped ceria.     

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.