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Porous cordierite ceramics were prepared from a mixture of coal fly ash and basic magnesium carbonate at 1100–1350°C. Porosity, flexural strength and thermal expansion coefficient of the samples sintered at 1300°C were estimated to be 26%, 65 MPa and 4.21×10−6/°C, respectively. The kinetics of the formation progress was investigated by stepwise isothermal dilatometry (SID) accompanied with XRD, SEM and porosity measurement. It was found that the isothermal shrinkage data from SID could be well analyzed to get kinetic parameters according to the empirical rate equation developed by Makipirtti-Meng, dY/dt = nk(T)Y(1 − Y)(Y/1 − Y)n/1, where Y is the fractional shrinkage during the sintering process and n is a dimensionless component. The apparent activation energy ΔE values for 900–1000°C and 1050–1150°C were 1294 and 1778 kJ/mol, respectively.

A dense $${\text{BaCe}}_{{\text{0}}{\text{.8}}} {\text{Sm}}_{{\text{0}}{\text{.2}}} {\text{O}}_{{\text{3 - }}\delta } $$ (BCSO) membrane was fabricated by a modified suspension spraying on porous NiO–BCSO anode support. In the process, the suspension was directly prepared by ball-milling the BaCO3, CeO2, and Sm2O3 powders in ethanol. A dense and uniform electrolyte layer in the thickness of 10 μm was successfully prepared on porous anode support by suspension spray process after co-sintering at 1,400 °C for 5 h. With $${\text{Nd}}_{{\text{0}}{\text{.7}}} {\text{Sr}}_{{\text{0}}{\text{.3}}} {\text{MnO}}_{{\text{3 - }}\sigma } $$ (NSMO) cathode, a single cell was assembled and tested with hydrogen and ammonia as fuels, respectively. The hydrogen-fueled cell exhibits 1.01 V for open circuit voltage (OCV) and 560 mW/cm2 for peak power density at 700 °C. In comparison, the cell in ammonia displays a similar performance (1.02 V for OCV and 530 mW/cm2 for output), which indicates the liquid ammonia is a promising substitute for hydrogen. Moreover, the fuel cell displays good interface contacts. To sum up, ammonia-fueled solid oxide fuel cells prepared by this simple suspension spray is an alternative way to promote the commercialization.

NiO/SDC composites and Ni/SDC cermets for solid oxide fuel cell (SOFC) anode applications were prepared from nickel oxide (NiO) and samaria doped ceria (SDC) powders by the powder metallurgy process. The physical and mechanical properties, as well as the microstructure of the NiO/SDC composites and the Ni/SDC cermets were investigated. It is shown that the sintering temperature of the NiO/SDC composites and NiO content plays an important role in determining the microstructure and properties of the NiO/SDC composites, which, in turn, influences the microstructure, electrical conductivity, and mechanical properties of the Ni/SDC cermets. The present study demonstrated that composition and tprocess parameters must be appropriately selected to optimize the microstructure and the properties of NiO/SDC materials for solid oxide fuel cell applications.

The electromotive force (e.m.f) is calculated for solid oxide fuel cells (SOFCs) based on doped ceria electrolytes using biomass-produced gases (BPG, 14.7% CO, 14.2% CO2, 15.3% H2, 4.2% CH4, and 51% N2) as fuels and air as oxidant. It reveals that the BPG derived e.m.f. is very close to hydrogen when doped ceria is used as the electrolyte. A 35-μm-thick samaria-doped ceria based single cell was tested between 450 and 650 °C using BPG as fuel. Maximum power density of about 700 mW cm−2 was achieved at 650 °C. The open-circuit voltage at 450 °C was 0.96 V, close to the calculated value. However, the cell power density using BPG as fuel was relatively lower than that using humidified hydrogen (3% H2O), and close to that using humidified methane (3% H2O). Impedance measurements indicate that the relatively lower power output may be attributed to the high anode--electrolyte interfacial polarization resistance when BPG is used as fuel.

Yttria-stabilized zirconia (YSZ) thin films were prepared by conventional and modified dip-coating techniques followed by heating to an appropriate temperature in air. Scanning electron microscopy showed that films of the thickness ranging from 20 to 30 μm were dense and crack-free. The electrical properties of the films were investigated by ac impedance spectroscopy. La0.8Sr0.2MnO3 paste was printed on to a YSZ electrolyte/anode assembly to create single fuel cells which were tested in the temperature range 650–800 °C. The results showed that both open circuit voltage (OCV) and maximum power density values of the cells with electrolytes produced by the modified dip coating were higher than those fabricated by conventional processing. At 800 °C, the OCV reached 0.98 V and a maximum power density of 190 mW cm−2 was attained, demonstrating that the modified dip coating process is a simple and cost-effective fabrication technique for IT-SOFCs, though further improvement is necessary.

Sr- and Mn-doped lanthanum gallate powders (LSGMn, La0.9Sr0.1Ga1 − xMnxO3 − δ, x = 0.20, 0.35, 0.43) were prepared by glycine-nitrate combustion synthesis. X-ray diffraction patterns indicate the perovskite structure was formed without any second phase after calcining the powders at 1000°C for 4 h. Compacts of powders synthesized under stoichiometric combustion were sintered to densities over 95% of theoretical values. The electrical conductivity of this material in both air and H2 were characterized using AC impedance spectroscopy. It showed that the conductivity in H2 atmosphere is lower than that in air due to p-type electrical conduction in this material, and the electrical conductivity increases remarkably with increasing manganese content. Good chemical stability of La0.9Sr0.1Ga1 − xMnxO3 − δ in H2 atmosphere as well as the relatively high conductivity makes it an appropriate anode material for Sr- and Mg-doped lanthanum gallate (LSGM)-based IT-SOFCs. Preliminary fuel cell performance measurements were performed, showing promising electrochemical properties of such anode materials.

A gelcasting process has been successfully employed to fabricate porous mullite-corundum ceramic composites from natural clay and corundum powders. The specimens based on the mullite composition are found with an open porosity of 45–47.9%, mean pore size of 1.28–2.55 μm, and nitrogen permeability of 965–5038 m3· m−2· bar−1· hr−1by reactively sintering the gelled mixture of kaolinite and α-alumina at 1100–1500°C. The open porosity (ρo), mean pore size (dp), pore size distribution and gas permeability can be controlled by adjusting raw material ratios and sintering temperatures. The gas permeability of the specimens is found to be more dependent on the pore size distribution as well as dpthan on ρo. In addition, the gas transportation mechanism in porous mullite-corundum ceramic composites is dominated by viscous flow.

Fine $$ SrTiO_3 $$ and Sr(Mg0.4Ti0.6)O3–δ powders were prepared by a sol-precipitation method. Tetraisopropyl titanate was used as a starting material, which firstly chelated with the acetic acid to form a water-soluble titanyl precursor. This precursor was then precipitated in a strong NaOH solution, to which, a nitrate solution of the required ratio of $$ Mg^{2 + } /Sr^{2 + } $$ was also added. By properly controlling reaction conditions, high crystalline undoped and Mg-doped strontium titanates with the dominating perovskite structures could be obtained directly at 80 °C. Owing to the chelating reaction of tetraisopropyl titanate with the acetic acid, the problem of the premature hydrolysis of titanium precursor was circumvented. The rates of the hydrolysis and condensation of titanyl acylate were also diminished. The final powder obtained had a uniform particle size of 40–60 nm. The formation mechanisms of $$ SrTiO_3 $$ and Sr(Mg0.4Ti0.6)O3–δ were also discussed. This study indicated that in the entire sol-precipitation process, the mixing of cations was homogeneous and the diffusion of alkaline earth cations into titanium particles occurred all at atomic level, which allowed the realization of the optimized solid-solubility in the complex oxide system. This method could be exploited for the preparation of other doped titanates.

Proton conducting and oxygen-ion conducting materials are widely studied for their applications in fuel cells, electrolysis cells, electrochemical reactors, and sensors [1±3]. Proton electrolyte materials, include water-containing materials (HUP, etc.), oxo acids and their salts (CsHSO4, etc.), and complex oxides (MCeO3, MZrO3, etc., where M ˆ Ca, Sr, Ba) [2]. The transportation of proton is based on the hydrogen-bond defects incorporated into the oxides or the rotation of tetrahedral XO4 [1±3]. In a word, most proton and=or oxygen-conducting materials are oxygen-containing materials. Furthermore, the well-known proton-conducting materials (MCeO3, MZrO3, etc.) and oxygen-conducting materials (YSZ, etc.) all operate at high temperatures (800± 1100 8C). Recently, in our experiments we found that a NaCl-based composite electrolyte showed distinct proton and oxygen ion conduction at intermediate temperatures. Moreover, pure NaCl belongs to the non-oxygen material systems, which are obviously different from the usual H‡ and O2y conductors. Compared with the reported proton and oxygen conductors, this material is very cheap and easily available, which will lower the operational cost of electrochemical devices using it as electrolyte. Sodium chloride was sintered at 850 8C for 2 h, pressed into tablets, coated with platinum paste on both sides, and calcined at 600 8C for 3 h to form porous electrodes before electrochemistry measurements. In this work, the H2=O2 fuel cell with pure NaCl as electrolyte (Fig. 1a) resulted in a current density of 70 mA cmy2 at a 100 mV terminal voltage, indicating that pure NaCl, which is a nonoxygen material, exhibits proton and=or oxygen ion conduction. To improve the structural strength and performance of the cells, a-Al2O3 was mixed with NaCl and this material was given the same experimental process as described previously. Of course, the NaCl-Al2O3 composite cannot be classi®ed as non-oxygen material system. The experimental results for both hydrogen and oxygen concentration cells indicate that the composite materials have both proton and oxygen conductivity between 650± 750 8C. In NaCl-Al2O3, composite solid electrolytes with a composition of 30 mol % Al2O3 have the highest conductivity in air [4, 5]. However, to our knowledge, no report on the proton or oxygen ion conduction of that material appears. The sintered tablets of pure inorganic salts usually have poor construction strength. The addition of a second phase (such as Al2O3, CeO2, SiO2) not only greatly improves the mechanical strength but it enhances the conductivity of the materials [6±8]. Therefore, in our experiments, we have mainly studied the properties of the hydrogen concentration cell (HCC), oxygen concentration cell (OCC), and the H2=O2 fuel cell of NaCl-Al2O3 composite electrolytes containing 30 mol % a-Al2O3. High-purity NaCl and a-Al2O3, with molar ratio of 7:3 were mixed

Perovskite La0.6Sr0.4Co0.8Fe0.2O3−δ (LSCF) powders have been successfully synthesized from oxide and carbonates based on the principle of gelcasting. Phase-forming temperature is very dependent on the ball-milling process during the suspension preparation. As the ball-milling time is increased, the temperature of phase formation decreases, therefore the perovskite powder obtained has a larger Brunaver–Emmett–Teller (BET) specific surface area. The grain sizes were around 1 μm at 1000°C and 2 μm at 1100°C from scanning electron microscopy (SEM) photographs. The perovskite powders have good sinterability: the sintering densities of ceramic bodies shaped with as-prepared powders were investigated. SEM photos show that sintered ceramics exhibit a well defined morphology in the packing and sintering of particles. The oxygen permeance of disc shaped samples, with a thickness ranging from 1.02 to 1.98 mm was 6.39 × 10−8–1.99 × 10−8 mol cm−2 s−1 at 900°C indicating that LSCF ceramics have high oxygen permeation. It can be concluded that gelcasting is a simple and effective method for preparing practical multicomponent perovskite powders.

This paper discusses hydrogen energy and the methods for production of hydrogen. It also provides a review of various materials which are hydrogen permeable. Previous studies on the proton-conducting ceramics and their properties are summarized. The principle of proton-conducting solid state fuel cell for conversing the energy of hydrogen containing fuel is described with a discussion of the advantages of proton-conducting ceramic fuel cells as compared to oxygen-ionic conducting fuel cells. The paper is concluded with a discussion of the major materials related technical challenges in the development of the proton-conducting ceramic fuel cells.

Thermal decomposition of BaC2O4·0.5H2O in air was studied by a combination of stepwise isothermal analysis (SIA) and non-isothermal thermogravimetry. The results from both techniques show that the crystal water is released in one step and that anhydrous barium oxalate is decomposed in one step, while BaCO3 decomposes in three steps to BaO, forming two intermediate compounds with the formulas of BaCO3·(BaO)2 and (BaCO3)0.5·(BaO)2.5. Reaction mechanism analyses using the data from SIA measurements show that the controlling mechanism for all the five decomposition steps in isothermal conditions is a two-dimensional phase-boundary controlled process. Kinetic parameters are obtained for the five decomposition steps from the non-isothermal thermogravimetric data.

The decomposition process of barium, cerium and neodymium oxalates in air was investigated by DTA-TG. Decomposition of an oxalate coprecipitate precursor and formation of barium cerate were examined in air, N2 and CO2 atmospheres, respectively, by employing DTA-TG and XRD. The results showed that, in air, cerium oxalate could easily be decomposed to CeO2 below 350°C and Nd2O3 could be obtained at 670°C, while a high temperature of >1400°C was needed to obtain BaO. Although some amount of BaCeO3 was formed at 500°C in air, at 650°C in N2 and at 800°C in CO2, single perovskite phase of BaCeO3 could only be obtained at a much higher temperature.

Single-phase YBa[sub 2]Cu[sub 3]O[sub 7[minus][delta]] thin films with Tc values around 90 K are readily obtained by using a single-source chemical vapor deposition technique with normal precursor mass transport. The quality of the films is controlled by adjusting the carrier gas flow rate and the precursor feed rate. 3 refs., 2 figs.