Electrophoretic deposition of ceramic materials for fuel cell applications

La_0.8Sr_0.2Ga_0.875Mg_0.125O_3-x (LSGM), La_0.8Sr_0.2Co_0.2Fe_0.8O_3-δ (LSCF), yttria stabilized zirconia (YSZ) and (Ce_0.8Gd_0.2)O_1.9 (CGO) were electrophoretically deposited on Ni foils and Ni-yttria stabilized zirconia substrates prepared by tape casting. It was demonstrated that the ethyl alcohol–phosphate ester–polyvinyl butyral system is an effective solvent–dispersant–binder system for electrophoretic deposition of these materials. The influence of dispersant, binder and current density on deposition efficiency and deposit morphology was studied. The microstructure of the deposits was examined by electron microscopy. The proposed solvent–dispersant–binder medium for electrophoretic deposition of LSGM, LSCF, YSZ and CGO has important advantages and implications in fuel cell design.     

Phase interaction and oxygen transport in La0.8Sr0.2Fe0.8Co0.2O3–(La0.9Sr0.1)0.98Ga0.8Mg0.2O3 composites

Composite ceramics made of two perovskite-type compounds, (La_0.9Sr_0.1)_0.98Ga_0.8Mg_0.2O_3−δ (LSGM) and La_0.8Sr_0.2Fe_0.8Co_0.2O_3−δ (LSFC) mixed in the ratio 60:40 wt.%, possess relatively high oxygen permeability limited by both bulk ionic conduction and surface exchange at 700−950 °C. Sintering at elevated temperatures (1320–1410 °C) necessary to obtain dense materials leads to fast interdiffusion of the components, forming almost single perovskite phase ceramics with local inhomogeneities. This phase interaction decreases the oxygen ionic transport in the composites, where the level of ionic conductivity is intermediate between those of LSGM and LSFC. The scanning electron microscopy (SEM) suggests a presence of Ga-enriched domains, probably having a high ionic conductivity. The size and concentration of these domains can be increased by decreasing sintering temperature or using preliminary coarsened LSGM powders. The maximum oxygen permeability is thus observed for the composite prepared under minimum sintering conditions sufficient to obtain gas-tight ceramics, including the use of LSGM, preliminary passivated at 1150 °C, and sintered at 1320 °C. The activation energy values for total conductivity, which is predominantly p-type electronic and slightly decreases due to component interaction, vary in the narrow range from 24.0 to 26.2 kJ/mol at 25–575 °C. The average thermal expansion coefficients (TECs) of LSGM-LSFC composites, calculated from dilatometric data in air, are (12.4–13.5)×10⁻⁶ K⁻¹ at 100–650 °C and (17.8–19.8)×10⁻⁶ K⁻¹ at 650–1000 °C.     

Influence of microstructure and architecture on oxygen permeation of La(1−X)SrXFe(1−Y)(Ga,Ni)YO3−δ perovskite catalytic membrane reactor

Catalytic membrane reactors (CMR) have been an economically attractive process for natural gas reforming to syngas (H₂ + CO) since more than twenty years.The CMR studied in this paper consists of a mixed ionic and electronic conductor dense layer (La_(1?X)Sr_XFe_(1?Y)Ga_YO_3?δ). High temperature X-ray diffraction analysis, from room temperature to 900 °C under air and nitrogen atmosphere, show a reversible monoclinic to rhombohedral phase transition around 300 °C, and good chemical and dimensional stabilities of La_0.8Sr_0.2Fe_0.7Ga_0.3O_3?δ material.The La_0.8Sr_0.2Fe_0.7Ga_0.3O_3?δ dense layer elaborated by tape casting has been respectively coated with La_0.8Sr_0.2Fe_0.7Ga_0.3O_3?δ on the air side and La_0.8Sr_0.2Fe_0.7Ni_0.3O_3?δ on the inert side using screen printing. The influences of the dense membrane microstructure and of the surface exchange kinetics on the oxygen semi-permeation performances are evaluated. Small grain size, mainly below 1 μm in the dense membrane significantly increases the oxygen flux. A porous layer of La_0.8Sr_0.2Fe_0.7Ni_0.3O_3?δ or La_0.8Sr_0.2Fe_0.7Ga_0.3O_3?δ on the air or inert side of the membrane increased strongly the specific oxygen semi-permeation. The impact of the porous layer is much more important than the reduction of the grain size. In this case, surface exchange kinetics are the limiting steps of oxygen permeation, and Ni-containing formulation leads to the highest flux.     

Influence of Microstructure and Surface Activation of Dual‐Phase Membrane Ce0.8Gd0.2O2−δ–FeCo2O4 on Oxygen Permeation

Dual‐phase oxygen transport membranes are fast‐growing research interest for application in oxyfuel combustion process. One such potential candidate is CGO‐FCO (60 wt% Ce_0.8Gd_0.2O_2?δ–40 wt% FeCo₂O₄) identified to provide good oxygen permeation flux with substantial stability in harsh atmosphere. Dense CGO‐FCO membranes of 1 mm thickness were fabricated by sintering dry pellets pressed from powders synthesized by one‐pot method (modified Pechini process) at 1200°C for 10 h. Microstructure analysis indicates presence of a third orthorhombic perovskite phase in the sintered composite. It was also identified that the spinel phase tends to form an oxygen deficient phase at the grain boundary of spinel and CGO phases. Surface exchange limitation of the membranes was overcome by La_0.6Sr_0.4Co_0.2Fe_0.8O_3?δ (LSCF) porous layer coating over the composite. The oxygen permeation flux of the CGO‐FCO screen printed with a porous layer of 10 μm thick LSCF is 0.11 mL/cm² per minute at 850°C with argon as sweep and air as feed gas at the rates of 50 and 250 mL/min.     

Enhanced sintering of Ce0.8Nd0.2O2−δ-La0.8Sr0.2Ga0.8Mg0.2O3−δ using CoO as a sintering aid

Ce_0.8Nd_0.2O_1.9 (NDC) and La_0.8Sr_0.2Ga_0.8Mg_0.2O_3-δ (LSGM) electrolytes were prepared using a sol-gel method. NDC-LSGM composite electrolytes were subsequently prepared by adding 5% (w, mass fraction) precalcined LSGM powders to NDC sols. The electrolyte materials of NDC-Co and NDC-LSGM-Co were obtained by adding 1 mol% CoO to NDC sols and NDC-LSGM composite electrolytes, respectively. The microstructure and phase composition of the pellets were characterized using X-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM), and energy dispersive X-ray spectroscopy (EDS). The electrical conductivities of the pellets were measured using alternative current (AC) impedance spectroscopy. The results indicate that a single perovskite phase is observed for the LSGM ceramic, while NDC-Co, NDC-LSGM and NDC-LSGM-Co have a cubic fluorite structure similar to that of NDC. As a sintering aid, CoO can further promote grain growth and increase relative density (＞95%) of the NDC-LSGM composite electrolyte. The enhancement of the total conductivity is primarily attributed to the large increase in the conductivity of the grain boundary. However, the slight decrease of the grain boundary conductivity of the NDC-LSGM-Co electrolyte is caused by the presence of trace amounts of impurity phases in the grain boundaries.     

The Effect of Plasma Spraying Power on La0.58Sr0.4Co0.2Fe0.8O3–δ–La0.8Sr0.2Ga0.8Mg0.2O3–δ Composite Cathode Interlayer Microstructure and Cell Performance

The metal‐supported intermediate temperature solid oxide fuel cells with a porous nickel substrate, a nano‐structured LDC (Ce_0.55La_0.45O_2–δ)–Ni composite anode, an LDC diffusion barrier layer, an LSGM (La_0.8Sr_0.2Ga_0.8Mg_0.2O_3–δ) electrolyte, an LSCF (La_0.58Sr_0.4Co_0.2Fe_0.8O_3–δ)–LSGM composite cathode interlayer and an LSCF cathode current collector are fabricated by atmospheric plasma spraying. Four different plasma spraying powers of 26, 28, 30, and 34 kW are used to fabricate the LSCF–LSGM composite cathode interlayers. Each cell with a prepared LSCF–LSGM composite cathode interlayer has been post‐heat treated at 960 °C for 2 h in air with an applied pressure of 450 g cm^–2. The current‐voltage‐power and AC impedance measurements indicate that the LSCF–LSGM composite cathode interlayer formed at 28 kW plasma spraying power has the best power performance and the smallest polarization resistance at temperatures from 600 to 800 °C. The microstructure of the LSCF–LSGM composite cathode interlayer shows to be less dense and composed of smaller dense regions as the plasma spraying power decreases to 28 kW. The durability test of the cell with an optimized LSCF–LSGM composite cathode interlayer gives a degradation rate of 1.1% kh^–1 at the 0.3 A cm^–2 constant current density and 750 °C test temperature.     

Semiconductor ionic based Sm0.2Ce0.8O2−δ-La0.6Sr0.4Fe0.8Cu0.2O3-δ heterostructure for low temperature ceramic fuel cells

Structural design/doping strategy is an efficient method to prepare electrolytes with high oxygen ionic conductivity, but there is still hindrance for solid oxide fuel cell (SOFC) commercialization. Recent advances in semiconductor ionic materials have developed a novel strategy in designing low-temperature electrolyte materials. Here, a heterostructure composite of LSFC (La_0.6Sr_0.4Fe_0.8Cu_0.2O_3-δ) and SDC (Sm_0.2Ce_0.8O_2?δ) is developed. The LSFC-SDC composite exhibits a high ionic conductivity, >0.1S/cm at 550 °C. With symmetrical NCAL (Ni_0.8Co_0.15Al_0.05LiO_2-δ)-coated electrode, cells with SDC-LSFC electrolyte exhibit high open-circuit voltage (OCV), and achieve a significant power improvement (>1000 mW/cm²) compared with pure SDC electrolyte at 550 °C. The short-term stability result has proven the operating ability of SDC-LSFC electrolyte under fuel cell environment (H₂/air). This work demonstrates a new developing route of low-temperature solid oxide fuel cell (LTSOFC), which is different from the conventional SOFC.     

Electrochemical behavior of mixed-conducting oxide cathodes in contact with apatite-type La10Si5AlO26.5 electrolyte

The electrochemical activity of porous La₂Ni_0.8Cu_0.2O_4+δ, La₂Ni_0.8Cu_0.2O_4+δ-Ag, La_0.8Sr_0.2Fe_0.8Co_0.2O_3−δ-Ce_0.8Gd_0.2O_2−δ and La_0.7Sr_0.3MnO_3−δ-Ce_0.8Gd_0.2O_2−δ electrodes in contact with apatite-type La₁₀Si₅AlO_26.5 solid electrolyte has been appraised at 873-1073 K in air. The polarization resistance of nickelate-based cathodes is substantially higher compared to similar layers applied onto (La_0.9Sr_0.1)_0.98Ga_0.8Mg_0.2O_3−δ, whilst the corresponding activation energies, 69-74 kJ/mol, are close to the E_a values for ionic conduction in these electrolytes. The relatively low performance is primarily associated with the surface diffusion of silica from La₁₀Si₅AlO_26.5, which partially blocks the electrochemical reaction zone without formation of secondary phases detectable by X-ray diffraction. The oxygen reduction kinetics is also strongly influenced by the transport properties of solid electrolyte and by the exchange-related processes at the electrode surface. The role of the latter factor becomes evident on increasing current density, and in the cases when ionic conductivity of the electrode materials is low. As for other solid oxide electrolyte cells, the performance of mixed-conducting cathodes applied onto La₁₀Si₅AlO_26.5 can be improved by incorporating electrocatalytically-active components, such as Ag and PrO_x, and by reducing electrode fabrication temperature.     

Electrochemical characteristics of La0.6Sr0.4Co1−yFeyO3 (y=0.2–1.0) fiber cathodes

Electrospun La_xSr_1−xCo_1−yFe_yO₃ (LSCF) fibers with y=0.2 – 1.0 have been investigated as the cathode of intermediate solid oxide fuel cells (IT-SOFC). The electrochemical performances of LSCF (y=0.2–1.0) fibers were studied by impedance spectroscopy in symmetrical cells containing gadolinium doped ceria (CGO) electrolyte and LSCF electrode infiltrated with CGO. Impedance measurements showed that the impedance spectra have two or three semicircles, depending on the measurement temperature. The LSCF electrodes with higher cobalt content exhibit lower polarization resistance (R_p) and the La_0.6Sr_0.4Co_0.8Fe_0.2O₃ electrode displayed the lowest polarization resistance between 500 and 900 °C, classifying this composite cathode as a promising material for intermediate temperature SOFC based on CGO electrolyte.     

Effect of A-site ion nonstoichiometry on the chemical stability and electric conductivity of strontium and magnesium-doped lanthanum gallate

A series of Sr-ion deficient perovskites La_0.8Sr_0.2−xGa_0.8Mg_0.2O_2.8−δ (LSGM8282, x = 0.00, 0.05, 0.10, 0.15, 0.20), was synthesized by a conventional solid-state reaction method and their electric conductivity and chemical reactivity with Gd-doped ceria were investigated. Reactivity tests between the LSGMs and Ce_0.9Gd_0.1O_2−δ (GDC) were carried out by X-ray diffraction, SEM-EDS, and electric conductivity measurements. The Sr-ion deficient LSGMs have a lower reactivity against the formation of high-resistivity phases than the stoichiometric (x = 0.00) LSGM. The reaction layer formed at the interface of LSGM and GDC during the sintering process due to the mutual diffusion of the cations was classified into five layers depending on the composition. The introduction of the Sr-ion deficient LSGM suppressed the formation of the highly resistive Sr-rich (La_1+xSr_1−x)Ga₃O_7−δ phase. It was suggested that the Sr-ion deficient LSGM (La_0.8Sr_0.2−xGa_0.8Mg_0.2O_2.8−δ) of x = 0.15 was the best composition for suppressing the reaction with the GDC interlayer while retaining a relatively good electric conductivity.     

Electrical and stability performance of anode-supported solid oxide fuel cells with strontium- and magnesium-doped lanthanum gallate thin electrolyte

Anode-supported solid oxide fuel cells (SOFCs) comprising NiO-samarium-doped ceria (SDC) (Sm_0.2Ce_0.8O_1.9) composite anode, thin tri-layer electrolyte, and La_0.6Sr_0.4Co_0.8Fe_0.2O₃ (LSCF)-La_0.9Sr_0.1Ga_0.8Mg_0.2O_3−δ (LSGM) composite cathode were fabricated. The thin tri-layer consisting of an 11-μm thick LSGM electrolyte layer and a 12-μm thick La_0.4Ce_0.6O_1.8 (LDC) layer on each side of the LSGM was prepared by centrifugal casting and co-firing technique. The performance of the cells operated with humidified H₂ as fuel and ambient air as oxidant showed a maximum power density of 1.23 W cm⁻² at 800 °C. A stability test of about 100 h was carried out and some deterioration of output power was observed, while the open circuit voltage (OCV) kept unchanged. Impedance measurements showed that both the electrolyte ohmic resistance and the electrode polarization increased with time and the latter dominated the degradation.     

Electron-hole transport in (La0.9Sr0.1)0.98Ga0.8Mg0.2O3−δ electrolyte: effects of ceramic microstructure

The oxygen ion transference numbers of a series of (La_0.9Sr_0.1)_0.98Ga_0.8Mg_0.2O_3−δ (LSGM) ceramics with different microstructures, prepared by sintering at 1673 K for 0.5-120 h, were determined at 973-1223 K by a modified Faradaic efficiency technique, taking electrode polarization into account. In air, the transference numbers vary in the range 0.984-0.998, decreasing when temperature or oxygen partial pressure increases. Longer sintering times lead to grain growth and to the dissolution of Sr-rich secondary phases and magnesium oxide, present in trace amounts at the grain boundaries, into the major perovskite phase. This is accompanied with a slight decrease of the total grain-interior resistivity and thermal expansion, while the boundary resistance evaluated from impedance spectroscopy data decreases 3-7 times. The electron-hole transport in LSGM ceramics was found to decrease when the sintering time increases from 0.5 to 40 h, probably indicating a considerable contribution of acceptor-enriched boundaries in the hole conduction. Due to reducing boundary area in single-phase materials, further sintering leads to higher p-type conductivity. The results show that, as for ionic conductivity, electronic transport in solid electrolytes significantly depends on ceramic microstructure.     

Tuning Ba0.5Sr0.5Co0.8Fe0.2O3-δ cathode to high stability and activity via Ce-doping for ceramic fuel cells

Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3-δ (BSCF) fuel-cell cathode stands out because of its ultrahigh ionic conductivity and excellent electrocatalytic activity, but it is still very subject to instability. Here, a new strategy of Ce doping is proposed to boost the stability and activity of the BSCF cathode. A one-pot combustion method is employed to synthesize (Ba_0.5Sr_0.5)_1–xCe_xCo_0.8Fe_0.2O_3-δ (x=0–0.2) cathodes. Both BSCF and (Ba_0.5Sr_0.5)_0.9Ce_0.1Co_0.8Fe_0.2O_3-δ have a cubic perovskite structure. (Ba_0.5Sr_0.5)_0.8Ce_0.2Co_0.8Fe_0.2O_3-δ shows two phases of cubic perovskite and fluorite ceria. Proper Ce doping can boost the electrical conductivity of BSCF, and can dramatically reduce the polarization resistance of BSCF cathode. Ce doping significantly improved BSCF cathode long-term stability by 160 h. Moreover, ten-percent Ce doping in BSCF highly improves single-cell output performance from 516.33 mW cm^?2 to 629.75 mW cm^?2 at 750 °C. The results reveal that Ce doping as a potential strategy for enhancing the stability and activity of BSCF cathode is promising.     

Creep behavior of porous La0.6Sr0.4Co0.2Fe0.8O3-δ substrate material for oxygen separation application

Advanced oxygen transport membrane designs consist of a thin functional layer supported by a porous substrate material that carries mechanical loads. Creep deformation behavior is to be assessed to warrant a long-term reliable operation at elevated temperatures. Aiming towards an asymmetric composite, the current study reports and compares the creep behavior of La_0.6Sr_0.4Co_0.2Fe_0.8O_3-δ (LSCF) perovskite porous substrate material with different porosity and pore structures in air for a temperature range of 800–1000?°C. A porosity and pore structure independent average stress exponent and activation energy are derived from the deformation data, both being representative for the LSCF material. To investigate the structural stability of the dense layer in an asymmetric membrane, sandwich samples of Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3-δ (BSCF) and La_0.6Sr_0.4Co_0.2Fe_0.8O_3-δ (LSCF) with porous substrate and dense layers on both side were tested by three-point bending with respect to creep rupture behavior of the dense layer. Creep rupture cracks were observed in the tensile surface of BSCF, but not in the case of LSCF.     

Copper-based electrodes for IT-SOFC

Copper and gadolinium doped ceria (GDC) anode supported fuel cells were co-sintered at relatively low temperature (900 °C) and successfully tested in the intermediate temperature (IT) range. The GDC electrolyte densification was promoted by a compressive strain induced by increasing the anodic thickness and was evaluated by SEM investigation. Instead of more commonly used La_0.8Sr_0.2Fe_0.6Co_0.4O_3-δ, strontium and copper-doped lanthanum ferrite La_0.8Sr_0.2Fe_0.8Cu_0.2O_3-δ (LSFCu) mixed with 30 wt% GDC (LSFCu-GDC) was employed as cathodic material. Preliminary tests on Cu-GDC/GDC/LSFCu-GDC single cells showed promising results at temperature as low as 650 °C using hydrogen as fuel.     

Enhancing the sinterability and electrical properties of BaZr0.1Ce0.7Y0.2O3-δ proton-conducting ceramic electrolyte

A novel strategy was proposed to enhance the sinterability and electrical properties of BaZr_0.1Ce_0.7Y_0.2O_3-δ (BZCY) proton-conducting electrolyte by adding 10 wt.% La_0.9Sr_0.1Ga_0.8Mg_0.2O_3-δ (LSGM) to form a 90 wt.% BZCY–10 wt.% LSGM (BL91) composite electrolyte. XRD patterns showed that no reaction occurred between the BZCY and LSGM electrolytes after sintering at 1400°C, 1450°C, 1500°C, and 1550°C for 10 h. The BL91 composite electrolyte exhibited higher relative densities and Vickers hardness and excellent electrical properties compared with those of the BZCY electrolyte. A combined approach of equivalent circuit model and distribution of relaxation time analysis was used to distinguish the bulk and grain-boundary contributions to the total conductivity and electrode processes. The introduction of 10 wt.% LSGM serves as a grain-boundary pinning phase, which can reduce the mobility of grain boundaries, thereby increasing sintered density and enhancing conductivity in BL91. A solid oxide fuel cell with proton-conducting BL91 and BZCY membranes was tested, in which the former displayed higher power outputs than the latter. Ohmic and interfacial polarization resistances decreased by approximately 20%, thereby revealing the remarkable electrical properties of the BL91 electrolyte. Results demonstrated that BL91 composite is a development prospect proton-conducting electrolyte.     

A redox−reversible perovskite electrode for CeO2− and LaGaO3−based symmetric solid oxide fuel cells

Perovskite oxide SrFe_0.9Mo_0.1O_3?δ (SFM) was evaluated as the electrode for symmetric solid oxide fuel cells (S–SOFCs) with Sm_0.2Ce_0.8O_2?δ (SDC) and La_0.9Sr_0.1Ga_0.8Mg_0.2O_3?δ (LSGM) electrolytes. Under reducing conditions at 800 °C, the SFM was reduced to be a multi-phase composite consisting of the single perovskite phase, Ruddlesden–Popper (RP) layered perovskite phase, and Fe⁰ phase. After reoxidation at 800 °C in air, this multi?phase system was again transformed into the parent perovskite phase again, indicating good redox reversibility of the SFM. At 700 °C, polarisation resistances of the SFM used as the cathodes on the LSGM and SDC electrolytes were 0.28 and 0.14 Ω cm², respectively, in air. Using H₂ as a fuel, the LSGM and SDC supported S–SOFCs with the SFM symmetric electrodes showed the peak power outputs of 253 and 269 mW cm^?2, respectively, at 700 °C. Finally, the good long-term stability and redox-cycling stability of the S–SOFCs further demonstrate the potential of the SFM as the symmetric electrode.     

Ca and Pr substitution promoted the cell performance in LnSr3Fe3O10-δ cathode for solid oxide fuel cells

The substitution of Ca for Sr in the LnSr_3-xCa_xFe₃O_10-δ (x = 0–1.5, Ln = La, Pr, and Sm), Ruddlesden-Popper (RP) intergrowth structure was investigated to determine how the physical and electrochemical properties of this potential cathode material in solid oxide fuel cells (SOFCs) are impacted. A small amount of Ca incorporated into the structure reduced the thermal expansion coefficient, improved the electrical conductivity, and increased power density by up to 30% of a La_0.8Sr_0.2Ga_0.8Mg_0.2O₃ electrolyte-supported single cell. The microstructure and oxygen permeability of the materials were independent of Ca substitution. A phase transformation of LaSr_3-xCa_xFe₃O_10-δ to perovskite was observed when the Ca composition of x > 1.0. Among the substitution of Pr and Sm for La in LaSr_2.7Ca_0.3Fe₃O_10-δ, only PrSr_2.7Ca_0.3Fe₃O_10-δ was pure with no phase transformation found. The co-substitution of Pr and Ca promoted the reduction of Fe, enhanced the oxygen permeation and active surface, and diminished the contact resistance at the cathode-electrolyte interlayer. The co-substitution of Ca and Pr delivered good electrochemical performance of approximately 354 mWcm⁻² at 800 °C on a 0.3 mm thick La_0.8Sr_0.2Ga_0.8Mg_0.2O₃ electrolyte-supported cell and the lowest area specific resistance (ASR).     

Synthesis and Characterization of Oxyanion‐Doped Cobalt Containing Perovskites

In this paper, we report the incorporation of borate, silicate and phosphate into La_0.6Sr_0.4Co_0.8Fe_0.2O_3–δ (LSCF) and Sr_0.9Y_0.1CoO_3–δ (SYC) cathode materials for solid oxide fuel cells (SOFCs). In the former, an increase in the electronic conductivity was observed, which can be correlated with electron doping due to the oxyanion doping favoring the introduction of oxide ion vacancies. The highest conductivity was observed for La_0.6Sr_0.4Co_0.76Fe_0.19B_0.05O_3–δ, 1190 S cm^–1 at 700 °C, in comparison with 431 S cm^–1 for undoped La_0.6Sr_0.4Co_0.8Fe_0.2O_3–δ at the same temperature. For Sr_0.9Y_0.1CoO_3–δ series the conductivity suffers a decrease on doping, attributed to any effect of electron doping being outweighed by the effect of partial disruption of the electronic conduction pathways by the oxyanion. Composites of these cathode materials with 50% CGO10 were examined on dense CGO10 pellets and the area‐specific resistances (ASR) in symmetrical cells were determined. The ASR values, at 800 °C, were 0.20, 0.08 and 0.11 Ω cm² for La_0.6Sr_0.4Co_0.8Fe_0.2O_3–δ, La_0.6Sr_0.4Co_0.76Fe_0.19B_0.05O_3–δ and La_0.6Sr_0.4Co_0.78Fe_0.195Si_0.025O_3–δ, respectively. For the SYC materials, the oxyanion‐doped compositions also showed an improvement in the ASR values with respect to the parent compounds, despite the lower electronic conductivity in these cases. This observation may be due to an increase in ionic conductivity due to oxyanion incorporation leading to the formation of oxide ion vacancies. In addition, the stability of these systems towards CO₂ was studied. For La_0.6Sr_0.4Co_0.8(1–x)Fe_0.2(1–x)M_xO_3–δ series, all compositions showed no evidence for reactivity with CO₂ between RT and 1000 °C. On the other hand, for the Sr_0.9Y_0.1Co_1–xM_xO_3–δ series, some reactivity was observed, although the CO₂ stability was shown to be improved on oxyanion doping. Thus, these results show that oxyanion doping can have a beneficial effect on the performance of perovskite cobaltite cathode materials.     

Durability and performance of CGO barriers and LSCF cathode deposited by spray-pyrolysis

Ce_0.9Gd_0.1O_1.95 (CGO) protective layers are prepared by two different methods to prevent the reaction between the Zr_0.84Y_0.16O_1.92 (YSZ) electrolyte and the La_0.6Sr_0.4Co_0.2Fe_0.8O_3-δ (LSCF) cathode. In the first method, the CGO layers are deposited by an airbrushing technique from an ink containing CGO particles without and with cobalt as sintering aids. The second strategy consists in preparing both a dense CGO barrier layer and a porous LSCF cathode by spray-pyrolysis deposition, in order to further reduce the fabrication temperature and minimize the reaction between the cell components. The samples prepared by spray-pyrolysis exhibit better performance and durability than those obtained by conventional sintering methods. The results suggest that the interfacial reactivity between YSZ and LSCF as well as the Sr-enrichment at the cathode surface can be avoided by using low-temperature fabrication methods and by operating at temperatures lower than 650?°C.