Search

Electrical conduction and oxygen diffusion mobility in the bixbyite (Ia3̅) and rhombohedral (R3̅) polymorphs of the Ln6MoO12−Δ(Ln = Er, Tm, Yb; Δ = δ, δ1, δ2; δ1 > δ2) heavy lanthanide molybdates, belonging to new, previously unexplored classes of potential mixed (ionic–electronic) conductors, have been studied in the range of 200–900 °C. The oxygen self-diffusion coefficient in bixbyite (Ia3̅) Yb6MoO12−δphase estimated by the temperature-programmed heteroexchange with C18O2was shown to be much higher than that for rhombohedral (R3̅) RI (with large oxygen deficiency) and (R3̅) RII (with small oxygen deficiency) Ln6MoO12−Δ(Ln = Tm, Yb; Δ = δ1; δ1 > δ2) oxides. According to the activation energy for total conduction in ambient air, 0.99, 0.93, and 1.01 eV in Er6MoO12−δ, Tm6MoO12−δ,and Yb6MoO12−δbixbyites, respectively, oxygen ion conductivity prevails in the range ∼200–500 °C. Oxygen mobility data for the rhombohedral Ln6MoO12−Δ(Ln = Er, Tm, Yb; Δ = δ1, δ2) phases RI and RII indicate that the oxygen in these phases exhibits mobility at much higher temperatures, such as those above 600–700 °C. Accordingly, below 600–700 °C they have predominantly electronic conductivity. As shown by total conductivity study of Ln6MoO12−δ(Ln = Er, Tm, Yb) bixbyites (Ia3̅) and rhombohedral phases Ln6MoO12−Δ(Ln = Er, Tm, Yb; Δ = δ1, δ2) (R3̅) in dry and wet air, the proton conductivity contribution exists only in Ln6MoO12−δ(Ln = Er, Tm, Yb) bixbyites up to 450–600 °C and decreases with a decreasing of the lanthanide ionic radius. The obtained data on the mobility of oxygen and the presence of proton contribution in bixbyites in the 300–600 °C temperature range make it possible to confirm unequivocally that Ln6MoO12−δ(Ln = Er, Tm, Yb) bixbyites are mixed electron–proton conductors at these temperatures.

Reticulated vitreous carbon (RVC) foams were manufactured by multiple replications of a polyurethane foam template structure using ethanolic solutions of phenolic resin. The aims were to create an algorithm of fine tuning the precursor foam density and ensure an open-cell reticulated porous structure in a wide density range. The precursor foams were pyrolyzed in inert atmospheres at 700°C, 1100°C and 2000°C, and RVC foams with fully open cells and tunable bulk densities within 0.09–0.42 g/cm3were synthesized. The foams were characterized in terms of porous structure, carbon lattice parameters, mechanical properties, thermal conductivity, electric conductivity, and corrosive resistance. The reported manufacturing approach is suitable for designing the foam microstructure, including the strut design with a graded microstructure.

Mechanical and thermal properties of SiC-porcelain ceramics were studied in the wide SiC content range of 0–95%. Microstructure evolution, shrinkage at sintering, porosity, mechanical strength, elastic modulus, coefficient of thermal expansion (CTE) and thermal conductivity were studied depending on SiC content. The optimal sintering temperature was 1200 °C, and the maximum mechanical strength corresponded to SiC content of 90%. Parametric evaluation of the ceramic thermal shock resistance revealed its great potential for thermal cycling applications. It was demonstrated that the open-cell foam catalyst supports can be manufactured from SiC-porcelain ceramics by the polyurethane foam replication process.

Doped La2-xRxMo2-yWyO9 (R= Bi, Gd, Pr, Sm, Nd; x=0-0.5, y=0.5-1) were synthesized via polymerized precursors method or high power mechanical milling (MM). The study of doped LAMOX genesis and structural properties using thermal analysis, XRD, SEM, IR and Raman spectroscopy has revealed that for all cations but Bi substituting La-position, the pure cubic b-phase is formed from polymerized precursors after calcination at 700degC. W-doped LAMOX have been obtained via low temperature calcination of MM products depending on W concentration. Due to a high dispersion of powders, high density pellets of doped LAMOX ceramics have been already obtained after annealing at 950degC. Their electrical conductivity measured by impedance spectroscopy depends on the doping cation nature being sufficiently high (up to 5.6[?]10-3 S/cm at 630 oC) at temperature below 650degC.

Porous ceramometal Al2O3/CoAlO/CoAl was studied by set of physicochemical techniques such as XRD, SEM, internal field 59Co and 27Al MAS NMR, and porosity measurements. They revealed the cermet containing three parts. First, cobalt-free large porous alumina particles which surrounded by the second oxide part representing spinel CoxAl3-xO4 (x=1,2,3) oxides. And third, oxygen-free metallic part consists of cobalt metal particles covered by Co-Al oxide protecting the metallic part from oxidation. Porosity measurements ascertained high porosity (60%) and good SSA (122 m2/g). Also the enhanced adsorption of microwaves due to metallic particles randomly distributed in oxides was found.

The present paper is devoted to optimization of composites (100-z) wt.% La1-ySryFe0.7Ni0.3O3-d - z wt.% Ce0.9Gd0.1O2-d (GDC) and study of the effect of Sr doping of perovskite and GDC content in the sample on structural and transport features of the composites. The results on the research of structural and microstructural features of the composites and their transport properties by using XRD, HRTEM, EDX analysis, electrical conductivity measurements, oxygen isotope heteroexchange and conductivity as well as weight relaxation techniques are presented and discussed.

Gradient permeable metallic substrate material consisting of two layers of NiAl alloy was developed for the SOFC design. The open-cell foam layer (thickness 1-2 mm, cell density 60 ppi) provides the structure robustness, while a thin (100-200 μm) mesoporous layer facilitates supporting functional layers. Cathode layers (LSM, LSFN and their nanocomposites with GDC or YSZ) and anode layers (NiO/YSZ, NiO/YSZ +Ru/Ln-Sr-Mn-Cr-O nanocomposite catalyst) were deposited by slip casting, electrophoretic deposition or air brushing. Thin (5-10 μm) YSZ layer was deposited by MO CVD. Power density up to 550 mW/cm2 at 700oC was obtained on button-size cells using wet H2-air feeds.

Apatitetype lanthanum silicates ATLS doped by Fe were prepared by using mechanical activation, and the effect of the nature of the dopant raw materials on the formation of ATLS was considered. Genesis of the formation of apatite was studied by XRD, IR, HRTEM, and Mössbauer and UVVis electron spectroscopy. The possibility of a partial substitution of Si in the apatite with a dopant and the mechanism of formation of ATLS in the course of mechanical activation depend on the dopant parent compound. The structural compatibility of La2O3, LaOH3, and apatite was shown to favor the rapid formation of apatitetype silicate by a clustertopotactic mechanism during mechanical activation, and the formation of an amorphous ferrosilicate intermediate in the case of the LaNO33SiO2precursor favors dopant incorporation into the apatite. However, dopant incorporation into the apatite structure was shown to be partially or fully hampered through milling when FeOOH and αFe2O3are used as reagents. Using crystalline hydrates as dopant precursors was shown to result in the formation of apatite through a dissociative mechanism.

Advances in design of materials for solid oxide fuel cells, oxygen and hydrogen separation membranes, and catalysts for biofuel conversion into syngas and hydrogen are reviewed. Application of new efficient techniques of material synthesis and characterization of their atomic-scale structure, transport properties, and reactivity allowed to develop new types of efficient cathodes and anodes for solid oxide fuel cells, asymmetric supported oxygen, and hydrogen separation membranes with high permeability and structured catalysts with nanocomposite-active components demonstrating high performance and stability to coking in steam/autothermal reforming of biofuels.

The present study is focused on the development of new SOFC cathode structures based on YSZ electrolyte and operating in the temperature range of 600-800oC. The corresponding cathode materials were manufactured from La0.8Sr0.2Fe0.6Ni0.4O3-d and La0.8Sr0.2Fe0.6Ni0.4O3-d/ Ce0.9Gd0.1O2 composites. Thin electrolyte diffusion barrier layer of Ce0.9Gd0.1O2 was deposited between the cathode and the electrolyte to prevent possible formation of low conducting phases. The electrochemical characterization and SEM study of SOFCs demonstrated an improved performance of the nano-composite SOFC cathode structures.

Al-doped La9.33+x/3+ySi6–xAlxO26+3y/2 (x = 0–1.5, y = 0–0.67) apatite-type lanthanum silicates (ATLS) were synthesized with a high-power (1200 rpm) planetary ball mill that allows the formation of the lanthanum silicate phase after milling for 20–35 min at room temperature. The apatite phase already appears after milling for 5 min. Phase, structural and microstructural studies on the nanocrystalline lanthanum silicates were carried out by using XRD, TEM, and IR, 27Al and 29Si MAS NMR spectroscopy to clarify the mechanism of ATLS formation. The cluster-topotactic mechanism of the formation of apatite by mechanochemical treatment involving hydration of the starting compounds and acid–base reactions is suggested. Al-doping results in promoting the formation of apatite. However, a secondary LaAlO3 phase may be present in the sample depending on its stoichiometry. This suggests the existence of a biphase domain in the La2O3–SiO2–Al2O3 phase diagram at room temperature, in which Al-doped apatite and LaAlO3 phases coexist. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)

The real structure of nanocrystalline CeO2-ZrO2 (Ce:Zr=1:1) systems prepared via the polymerized polyester precursor (Pechini) route and doped with La3+ or Gd3+ cations, up to 30 at.%, was studied by X-ray powder diffraction, EXAFS and Raman spectroscopy and the surface features characterized by XPS and SIMS. Undoped CeO2-ZrO2 system revealed nanoscale heterogeneity, perhaps due to the co-existence of Zr- or Ce-enriched domains. With large La3+ dopant the system remains bi-phasic within the studied ranges of composition, incorporation of the smaller Gd3+ cation stabilizes the single-phase solid solution. For both systems, the increase of dopant content was accompanied by a decline of domain size and an increase of the average lattice parameter of fluorite-like phases. Depletion of the surface layer by smaller Zr4+ cations was observed, while the surface content of a doping cation is either, close to that in the bulk (La) or below it (Gd). Such a spatial distribution of components results in some ordering of cations within the lattice. It is reflected in different modes of rearrangement of oxygen coordination polyhedra with the Gd or La content (distances and coordination numbers by EXAFS), and specificity of XRD patterns not conforming to a simple model with statistical distribution of oxygen vacancies.

Nanocrystalline CeO2-ZrO2 (Ce:Zr 1:1) samples doped with La, Pr or Gd cations (containing up to 30 at.%) were prepared via the Pechini route. Pt (1.4 wt.%) was supported via impregnation with H2PtCl6 solution followed by drying and calcination. The samples’ surface features were studied by SIMS and FTIRS of adsorbed CO. The oxygen mobility was characterized by the dynamic oxygen isotope exchange and H2 TPR. Catalytic activity was studied in the flow installation using diluted feeds (0.7% CH4 +0.5% O2 or 1% C3H6O + 0.5% O2 +0.5% H2O in He). In the selective oxidation of methane (POM), the catalytic activity correlates with Pt dispersion controlled by the oxidized sample’s ability to stabilize Pt2+ cations as precursors of small reactive Pt clusters formed under reaction conditions. This is favoured by a larger doping cation (La) and a developed network of nanodomain boundaries. At comparable Pt dispersion, the highest performance was demonstrated by a La-doped system, which correlates with the highest surface/near-surface oxygen mobility controlled by the strength of Ce-O bonds in the surface layer. In the autothermal reforming of acetone, the activity trends differ from those in POM because of the more prominent role of the oxygen mobility required to prevent surface coking.

Copper catalysts supported on alumina-doped zirconia were prepared by sol–gel processing followed by supercritical drying or aging in the mother solution at 100 °C. After drying and calcination, the catalyst supports were impregnated with a copper(II) nitrate aqueous solution by the incipient wetness method to achieve a Cu loading of about 2%. The samples showed ~90% NO conversion at 350–400 °C. The catalytic performance of these systems appears to be determined by the degree of clustering of copper cations as probed by FTIR spectroscopy of adsorbed CO.

Mechanoceramical synthesis of La1−xSrxCoO3(0≤x≤1) perovskites was made from simple oxides. Samples calcined at 900 and 1100°C for 4 h are nearly monophase and well crystallized. Sr adding was found to cause a structure rearrangement from the hexagonal (at x≤0.4) to the cubic one (at 0.8>x>0.4) and back to the hexagonal at x>0.8. There are two maxima of the catalytic activity versus chemical composition: at x=0.3 and at x=0.8. TEM data for these samples were obtained and disordered surface layers were detected. There is a correlation between the catalytic activity and surface layers microstructure.

Thermally stable cubic mesoporous zirconia samples stabilized by the alkaline-earth cations (Ca, Sr, Ba) were synthesized via the coprecipitation route followed by refluxing in the presence of surfactants. These systems were used as supports for copper cations and then modified by the addition of silver nanoparticles using impregnation or photoassisted deposition techniques. The structural, textural, and surface features of these nanosystems were studied by using TEM, X-ray diffraction, EXAFS, nitrogen adsorption isotherms, SAXS, FTIRS of adsorbed CO, and TPD of adsorbed NOxspecies. Partially stabilized zirconia samples were found to possess a disordered cubic structure. A higher tendency of bulky Ba cation to segregate in the surface layer is reflected in a higher degree of surface disordering, higher concentration of hydroxyls, and greater coordination unsaturation of isolated copper cations. In contrast to such traditional supports as γ-alumina, stabilized zirconia supports appear to favor formation of small reactive (probably, three-dimensional) clusters of copper cations possessing an increased reactivity and decreased strength of oxygen bonding with these cations. It is reflected in decreased thermal stability of surface nitrite and nitrate species located at these centers as compared with such species on the surface of CuO/alumina catalysts. This feature seems to be primarily determined by the specificity of the surface structure of fluorite-like supports (ceria, zirconia). Silver incorporation into copper oxidic clusters decreases the strength of copper–oxygen bonds as well as the thermal stability of adsorbed nitrite–nitrate species. For samples prepared via the photodeposition route, the clustering degree of copper cations is usually lower than in the case of samples obtained by traditional impregnation procedure.

The catalytic performances of copper oxidic species supported on mesoporous zirconia supports stabilized by alkaline earth cations were studied for the reactions of NO oxidation to NO2and the selective catalytic reduction (SCR) of NOxin excess oxygen. Three different types of hydrocarbon reductants were studied, namely, propane, propylene and the long-chain hydrocarbon decane. For comparison, the performance of CuO and CuO+Ag supported on alumina for the SCR of NOxby propane was also studied. This data was analyzed and discussed with reference to the information concerning the surface properties of these systems presented in Part 1 of this series. In general, for the same system, the maximum level of NOxconversion and temperature of maximum NOxconversion is strongly dependent upon the type of reducing agent. No universal relation was found between the surface density of coordinatively unsaturated cations able to activate hydrocarbons and the activity of the catalysts for the SCR reaction. In part, it can be explained by blocking the surface sites in reaction media either by strongly bound nitrate species or by coke. Addition of silver was found to be of significance only in the case of strong interaction between the metallic and oxidic components. Such a factor as the strength of oxygen and nitrate complexes bonding with the surface copper/copper–silver oxidic species depending upon the type of support and methods of samples synthesis appears to be the most important for performance of the systems studied in NOx-selective reduction by hydrocarbons in the presence of excess oxygen.

Calcium-substituted lanthanum manganites La1−xCaxMnO3+δ(0≤x≤1) were synthesized from the solid oxide precursors using two routes: a traditional ceramic method and the mechanical activation of the mixture of oxides in high power planetary ball mills, followed by the product annealing at different temperatures. The samples structure was studied by XPD and TEM methods, while their surface composition was characterized by the differential dissolution method. A pronounced effect of the preparation method on samples bulk and surface properties, reflected in their reactivity characterized by the rate of CO catalytic oxidation, was observed. For samples prepared via the ceramic route by sintering at 1100°C, continuous solid solutions are formed. In the case of mechanical activation route, by annealing of activated mixture of oxides at 700–100°C, solid solutions are formed only at the Ca content within 0≤x≤0.4 range. At higher Ca content, microheterogeneous composites are formed, in which the nucleus of particles is formed by the perovskite phase with x≤0.4, while the surface layer is enriched by Ca. The catalytic activity in CO oxidation appears to correlate with the density of extended defects, being decreased when Ca is segregated in the surface layer.

AbstractNanocomposites based upon framework zirconium phosphates with supported WO3, MoO3and Pt nanoparticles were synthesized via the incipient wetness impregnation of high-surface-area mesoporous phosphate samples with water solutions of corresponding salts followed by drying and calcination. The structure and surface properties of nanocomposites were studied by using combination of structural and spectral methods. Due to a strong interaction between supports and supported species, the structure of the latter differs considerably from that of the bulk phases. Surface acid centers typical for zirconium phosphates disappear suggesting their participation in bonding nanoparticles of promoters. Instead, new types of strong acid sites associated with tungsten oxide clusters emerge. The effect of these promoters on performance of zirconium phosphates in the reaction of pentane and hexane isomerization is considered.

AbstractHigh-power ball mill activation of the mixture of hydrated zirconium and lanthanum salts (oxonitrates, oxochlorides) with ammonium phosphate followed by hydrothermal treatment at temperatures not exceeding 200°C and a nearly neutral pH was found to yield crystalline dispersed phase of a cubic NH4Zr2(PO4)3type along with admixtures of disordered orthorhombic compounds of a zirconium orthophosphate type. In the same conditions and at the same Zr/P ratio, hydrothermal treatment of gels obtained by reacting mixed zirconium and lanthanum nitrates solutions with ammonium phosphates yields no crystalline products, and only treatment in acid media generates a phase of the α -ZrPO4(OH) type coexisting with the NH4Zr2(PO4)3phase if polyethylene oxide is present. X-ray powder diffraction, transmission electron microscopy, 31MAS-NMR, FTIRS and thermal analysis were applied to elucidate factors affecting crystallization of complex zirconium phosphates in the hydrothermal conditions. The most essential factor appears to be generation of some nuclei of zirconium phosphates under high pressures developed in the course of mixed solids mechanical activation. These nuclei are embedded into matrix of such well-crystallized solid products as ammonium nitrate or chloride. Hence, meta-stable cubic or orthorhombic structure of the phases obtained via mechanical activation route can be assigned to the nuclei-matrix orientation relationship. Due to easily scaled-up synthesis procedure, these results appear to be very promising for manufacturing of dispersed framework zirconium phosphates as acid catalysts or fast proton conductors.

This work aims at studying protonic transport of mixed proton–electron-conducting Nd5.5WO11.25-δ oxide synthesized by a citrate method as material for hydrogen separation membranes. Structure of samples was characterized by X-ray diffraction (XRD), and protonic mobility was studied using temperature-programmed desorption of H2O and isotope heteroexchange of the bulk protons with D2O as well as mass relaxation after an abrupt change of H2O partial pressure. The temperature range of Nd5.5WO11.25-δ efficient operation is 300–400 °C, where H+ tracer diffusion and chemical diffusion coefficients are ∼1 × 10−11 and ∼2 × 10−5 cm2/s, respectively, being comparable to or even better than those for similar systems. Hence, Nd5.5WO11.25-δ is a promising material for the design of hydrogen separation membranes.

Doped La2-xRxMo2-yWyO9(R= Bi, Gd, Pr, Sm, Nd; x=0-0.5, y=0.5-1) were synthesized via polymerized precursors method or high power mechanical milling (MM). The study of doped LAMOX genesis and structural properties using thermal analysis, XRD, SEM, IR and Raman spectroscopy has revealed that for all cations but Bi substituting La-position, the pure cubic β-phase is formed from polymerized precursors after calcination at 700°C. W-doped LAMOX have been obtained via low temperature calcination of MM products depending on W concentration. Due to a high dispersion of powders, high density pellets of doped LAMOX ceramics have been already obtained after annealing at 950°C. Their electrical conductivity measured by impedance spectroscopy depends on the doping cation nature being sufficiently high (up to 5.6∙10-3S/cm at 630 ºC) at temperature below 650°C.

A novel approach to the design of planar gradient porous supports for the thin-film SOFCs and MIEC membranes is described. The support's thermal expansion is controlled by the creation of a two-component composite metal-ceramic foam structure. Thin MIEC membranes and SOFCs were prepared on the composite supports by the layerwise deposition of composite functional layers including complex fluorites and perovskites. Lab-scale studies demonstrated promising performance of both MIEC membrane and SOFC.

The present paper is devoted to optimization of composites (100-z) wt.% La1-ySryFe0.7Ni0.3O3-δ - z wt.% Ce0.9Gd0.1O2-δ (GDC) and study of the effect of Sr doping of perovskite and GDC content in the sample on structural and transport features of the composites. The results on the research of structural and microstructural features of the composites and their transport properties by using XRD, HRTEM, EDX analysis, electrical conductivity measurements, oxygen isotope heteroexchange and conductivity as well as weight relaxation techniques are presented and discussed.

Procedures for the synthesis of nanocomposite anode materials comprised of Ni-YSZ promoted by doped Ce-Zr-O fluorite-like or La-Pr-Mn-Cr-O perovskite-like oxides and Pt/Ru were elaborated. Their composition, structure, reactivity, and catalytic properties in CH4 steam reforming were characterized using various techniques, such as SEM, TEM, EDX, TPR, and I-V testing in SOFC conditions. The optimized nanocomposites supported on compressed foam Ni-Al substrates demonstrated high and stable performance at H2O:CH4=1:2 ratio without coking or sintering. For the SOFC testing, the planar catalytic substrates with the surface area of 5x5 cm2 have been used. The demonstrated SOFC performance in the internal CH4 reforming mode was close to the performace obtained with the humidified hydrogen. The achieved power density was up to 300-800 mW/cm2 at 600-800 oC meeting the targets of the area specific resistance, fuel effficiency, and power density.

Ni/YSZ or Ni/ScCeSZ cermets were promoted by up to 10 wt?% of fluoritelike (Pr–Ce–Zr–?, La–Ce–Zr–?, and Ce–Zr–?) or perovskitelike (La–Pr–Mn–Cr–O) oxides and small (up to 1.4 wt?%) amounts of Pt group metals (Pd, Pt, or Ru). Reactivity of samples, their lattice oxygen mobility, and their ability to activate methane were characterized by temperature-programed reduction by CH4. The catalytic properties of these samples in methane steam reforming were studied at 500–850°C and short contact times (10 ms) in feeds with 8 mol?% of CH4 and steam/methane ratio of 1:3. Oxide promoters ensure stable performance of cermets in stoichiometric feeds at T>650°C by suppressing carbon deposition. Copromotion with precious metals enhances performance in the intermediate temperature (450–600°C) range due to more efficient activation of methane. Factors determining specificity of these cermet materials’ performance (chemical composition, microstructure, oxygen mobility in oxides, interaction between components, and reaction media effect) are considered. The most promising systems for practical application are Pt/Pr–Ce–Zr–O/Ni/YSZ and Ru/La–Pr–Mn–Cr–O/Ni/YSZ cermets demonstrating a high performance in the intermediate temperature range under broad variation in steam/CH4 ratio.

Ni/YSZ or Ni/ScCeSZ cermets were promoted by up to 10 wt % of fluoritelike (Pr–Ce–Zr–О, La–Ce–Zr–О, and Ce–Zr–О) or perovskitelike (La–Pr–Mn–Cr–O) oxides and small (up to 1.4 wt %) amounts of Pt group metals (Pd, Pt, or Ru). Reactivity of samples, their lattice oxygen mobility, and their ability to activate methane were characterized by temperature-programed reduction by CH4. The catalytic properties of these samples in methane steam reforming were studied at 500–850°C and short contact times (10 ms) in feeds with 8 mol % of CH4 and steam/methane ratio of 1:3. Oxide promoters ensure stable performance of cermets in stoichiometric feeds at T>650°C by suppressing carbon deposition. Copromotion with precious metals enhances performance in the intermediate temperature (450–600°C) range due to more efficient activation of methane. Factors determining specificity of these cermet materials’ performance (chemical composition, microstructure, oxygen mobility in oxides, interaction between components, and reaction media effect) are considered. The most promising systems for practical application are Pt/Pr–Ce–Zr–O/Ni/YSZ and Ru/La–Pr–Mn–Cr–O/Ni/YSZ cermets demonstrating a high performance in the intermediate temperature range under broad variation in steam/CH4 ratio.

This work presents results on synthesis and characterization of mixed ionic-electronic conducting nanocomposite cathode materials for Intermediate Temperature Solid Oxide Fuel Cells. The corresponding materials are comprised of La0.8Sr0.2MnO3 (LSM) or La0.8Sr0.2Fe1-xNixO3-δ (x=0.1-0.4) (LSFNx) perovskites and Sc0.1Ce0.01Zr0.89O2-x (ScCeSZ) or Ce0.9Gd0.1O2-δ (GDC) fluorites mixed via powerful ultrasonic dispersion of powders in isopropanol. Genesis of their structural properties was studied in detail by transmission electron microscopy with elemental analysis and X-ray diffraction; surface features were characterized by X-ray Photoelectron Spectroscopy. Perovskite-fluorite nanodomain interfaces appear to provide a path for fast oxygen diffusion as revealed by the oxygen isotope exchange and temperatureprogrammed desorption. Testing in wet H2/air for button-size fuel cells with thin Y-doped zirconia layer and nanocomposite functionally graded cathodes demonstrated promising and stable performance in some combinations in the intermediate temperature range.

The electrochemical characteristics of a La0.8Sr0.2Ni0.4Fe0.6O3 cathode electrode interfaced to La9.83Si5Al0.75Fe0.25O26{plus minus}δ apatite-type electrolyte were studied using AC impedance spectroscopy under open circuit conditions, at temperatures 600 to 800 oC and oxygen partial pressures in the range 0.1 to 20 kPa. The cathode and electrolyte powders were prepared via the Pechini method and the mechanochemical activation method, respectively. The electrocatalytic activity of the tested interface was assessed on the basis of its open circuit area specific polarization conductance , determined from the impedance data. The polarization conductance was found to increase with increasing , following power law dependence. The impedance characteristics of the system were determined by at least two different processes, corresponding to two partially overlapping depressed arcs in the Nyquist plots. The relative contribution and degree of overlap of these arcs depended on temperature and oxygen partial pressure.

Structural features of Fe- and Al-doped apatite-type lanthanum silicates with different stoichiometry have been studied by using XRD, XPS, IR, UV-Vis, EXAFS, Mossbauer, 29Si and 27Al MAS NMR spectroscopy. The transport properties of the samples were also characterized by using impedance spectroscopy and oxygen isotope heteroexchange.

The present study is focused on the development of new SOFC cathode structures based on YSZ electrolyte and operating in the temperature range of 600-800oC. The corresponding cathode materials were manufactured from La0.8Sr0.2Fe0.6Ni0.4O3-δ and La0.8Sr0.2Fe0.6Ni0.4O3-δ/ Ce0.9Gd0.1O2 composites. Thin electrolyte diffusion barrier layer of Ce0.9Gd0.1O2 was deposited between the cathode and the electrolyte to prevent possible formation of low conducting phases. The electrochemical characterization and SEM study of SOFCs demonstrated an improved performance of the nano-composite SOFC cathode structures.