High performance protonic ceramic membrane fuel cells (PCMFCs) with Ba0.5Sr0.5Zn0.2Fe0.8O3−δ perovskite cathode

Protonic ceramic membrane fuel cells (PCMFCs) based on proton-conducting electrolytes have attracted much attention because of many advantages, such as low activation energy and high energy efficiency. BaZr_0.1Ce_0.7Y_0.2O_3−δ (BZCY7) electrolyte based PCMFCs with stable Ba_0.5Sr_0.5Zn_0.2Fe_0.8O_3−δ (BSZF) perovskite cathode were investigated. Using thin membrane BZCY7 electrolyte (about 15 μm in thickness) synthesized by a modified Pechini method on NiO-BZCY7 anode support, PCMFCs were assembled and tested by selecting stable BSZF perovskite cathode. An open-circuit potential of 1.015 V, a maximum power density of 486 mW cm⁻², and a low polarization resistance of the electrodes of 0.08 Ω cm² was achieved at 700 °C. The results have indicated that BZCY7 proton-conducting electrolyte with BSZF cathode is a promising material system for the next generation solid oxide fuel cells.     

煤热解过程中含氮气相产物转化规律的实验研究

为了研究煤在热解过程中含氮气相产物的生成规律,在滴管炉反应系统中对四种原煤以及两种脱除矿物质煤样分别在500℃、700℃、900℃和1100℃进行了实验研究。结果表明,随着温度的升高,作为NO前驱物的HCN和NH3的收率随之增加,N2的收率也增加。煤种对含氮气相产物的生成规律也有着较大的影响,煤化程度比较低的煤在热解过程中,燃料氮向气相含氮产物的转化率较高;煤化程度比较高的煤转化率则偏低,大部分的氮缩聚在多环芳香结构中,成为焦炭氮。煤中的矿物质对燃料氮向N2的转化起到了促进作用,而对燃料氮向HCN和NH3的转化起到了抑制作用。     

A novel anode supported BaCe0.4Zr0.3Sn0.1Y0.2O3−δ electrolyte membrane for proton conducting solid oxide fuel cells

A novel BaCe_0.4Zr_0.3 Sn_0.1Y_0.2O_3−δ (BSY) electrolyte membrane with thickness of 20 μm was fabricated on NiO-based anode substrate via a one-step all-solid-state method followed by a co-sintering at 1450 °C for 5 h. Chemical stability test demonstrated that BSY electrolyte showed adequate chemical stability against CO₂ and H₂O at intermediate temperature. Besides, the doping of Sn also enhanced the conductivity in humidified hydrogen. With Nd_0.7Sr_0.3MnO_3−σ cathode and hydrogen fuel, the fuel cell generated maximum output of 320, 185 and 105 mW cm⁻² at 700, 650 and 600 °C, respectively. The interfacial resistance of the fuel cell was studied under open circuit conditions and the short-term cell performance also confirmed the stability of BSY electrolyte membrane.     

Effect of annealing temperature on the structural and optical properties of Zn1−xMgxO particles prepared by oxalate precursor

Zn_1−xMg_xO particles were prepared using zinc and magnesium oxalate precursor by co-precipitated method. The lattice constants of Zn_1−xMg_xO proved that the interstitial Mg formed at 500 °C and Mg replaced Zn in ZnO tetrahedral coordination at 800 °C. Compared with the ZnO, the absorbing band edge of the Zn_1−xMg_xO displayed blue shifts. The room temperature photoluminescence was similar to ZnO and variation of Mg content did not change the shape or peak position of the emission spectra markedly when it was annealed at 500 °C. However, its blue emission band disappeared, and a relatively strong green light emission at 498 nm appeared after annealed at 800 °C. The photoluminescence intensity ratios I_(green)/I_(UV) of Zn_1−xMg_xO varied with Mg content and the green light emission peak shifted from 498 nm to 472 nm when Mg content increased from 0 to 2.0 at.%.     

Anodic composite deposition of RuO2·xH2O–TiO2 for electrochemical supercapacitors

This communication demonstrates the first work on anodic composite deposition of oxide nanocomposites. Rutile TiO₂ nanoflowers with an average petal size of ca. 10 nm in diameter and 100 nm in length were synthesized from a TiCl₃ solution purged with air at 25 °C for 12 days prior to the composite deposition. Hydrous ruthenium oxide (RuO₂·xH₂O) and TiO₂ nanoflowers were composite-deposited onto Ti substrates for supercapacitors. In comparing with RuO₂·xH₂O deposits, RuO₂·xH₂O–TiO₂ nanocomposites with a highly porous nature exhibit the weakly mass-dependent specific capacitance and high-power capacitive characteristics.     

Synthesis of magnetic nickel spinel ferrite nanospheres by a reverse emulsion-assisted hydrothermal process

Nickel ferrite nanospheres were successfully synthesized by a reverse emulsion-assisted hydrothermal method. The reverse emulsion was composed of water, cetyltrimethyl ammonium bromide, polyoxyethylene(10)nonyl phenyl ether, iso-amyl alcohol and hexane. During the hydrothermal process, β-FeO(OH) and Ni_0.75Fe_0.25(CO₃)_0.125(OH)₂·0.38H₂O (INCHH) nanorods formed first and then transformed into nickel spinel ferrite nanospheres. The phase transformation mechanism is proposed based on the results of X-ray powder diffraction, transmission electron microscopy and energy-dispersive X-ray spectroscopy, etc. Nickel ferrite may form at the end of the INCHH nanorods or from the solution accompanied by the dissolution of β-FeO(OH) and INCHH nanorods. The X-ray photoelectron spectroscopy analysis shows that a few Fe³⁺ ions have been reduced to Fe²⁺ ions during the formation of nickel ferrite. The maximum magnetization of the nickel ferrite nanospheres obtained after hydrothermal reaction for 30 h is 55.01 emu/g, which is close to that of bulk NiFe₂O₄.     

Energetics of copper diphosphates – Cu2P2O7 and Cu3(P2O6OH)2

Differential scanning calorimetry and high temperature oxide melt solution calorimetry are used to study enthalpy of phase transition and enthalpies of formation of Cu₂P₂O₇ and Cu₃(P₂O₆OH)₂. α-Cu₂P₂O₇ is reversibly transformed to β-Cu₂P₂O₇ at 338–363 K with an enthalpy of phase transition of 0.15 ± 0.03 kJ mol⁻¹. Enthalpies of formation from oxides of α-Cu₂P₂O₇ and Cu₃(P₂O₆OH)₂ are −279.0 ± 1.4 kJ mol⁻¹ and −538.8 ± 2.7 kJ mol⁻¹, and their standard enthalpies of formation (enthalpy of formation from elements) are −2096.1 ± 4.3 kJ mol⁻¹ and −4302.7 ± 6.7 kJ mol⁻¹, respectively. The presence of hydrogen in diphosphate groups changes the geometry of Cu(II) and decreases acid–base interaction between oxide components in Cu₃(P₂O₆OH)₂, thus decreasing its thermodynamic stability.     

Activation of a single-chamber solid oxide fuel cell by a simple catalyst-assisted in-situ process

Initialization is a critical processing step that has thus far limited the application of the single-chamber solid oxide fuel cell (SC-SOFC). In-situ initialization of a SC-SOFC with a nickel-based anode by methane–air mixtures was investigated. Porous Ru–CeO₂ was used as a catalyst layer over a Ni-ScSZ cermet anode. Catalytic testing demonstrated Ru–CeO₂ had high activity for methane oxidation. The Ru in the catalyst layer catalyzed the formation of syngas, which successfully reduced the nickel oxide to metallic nickel in the anode. Single cells with a La_0.8Sr_0.2MnO₃ (LSM) cathode, initialized by this in-situ reduction method, delivered peak power densities of 205 and 327 mW cm⁻² at 800 °C and 850 °C, respectively. Such performances were better than those of the cell without the Ru–CeO₂ catalyst layer that was initialized by an ex-situ reduction method were.     

Investigation of Solid-Solid Interactions between Pure and Li2O-Doped Magnesium and Ferric Oxides

The results obtained showed that the addition of small amounts of LiNO₃ to the reacting mixed solids, consisting of equimolar proportion of Fe₂O₃ and basic MgCO₃ much enhanced the thermal decomposition of magnesium carbonate. The addition of 12 mol% LiNO₃ (6 mol% Li₂O) decreased the decomposition temperature of MgCO₃ from 525.5 to362°C. MgO underwent solid–solid interaction with Fe2O3 at temperatures starting from800°C yielding MgFe₂O₄. The amount of ferrite produced increased by increasing the precalcination temperature of the mixed solids. However, the completion of this reaction required prolonged heating at elevated temperature above 1100°C. Doping with Li₂O much enhanced the solid–solid interaction between the mixed oxides leading to the formation of MgFe₂O₄ phase at temperatures starting from 700°C. The addition of 6 mol% Li₂O to the mixed solids followed by precalcination at 1050°C for 4 h resulted in complete conversion of the reacting oxides into magnesium ferrite. The heat treatment of pure and doped solids at 900–1050°C effected the disappearance of most of IR transmission bands of the free oxides with subsequent appearance of new bands characteristic for MgFe₂O₄ structure. The promotion effect of Li2O towards the ferrite formation was attributed to an effective increase in the mobility of the various reacting cations. The activation energy of formation (ΔE) of magnesium ferrite was determined for pure and variously doped solids and the values obtained were 203, 126, 95 and 61 kJ mol⁻¹ for pure mixed solids and those treated with 1.5, 3.0 and 6.0 mol% Li₂O, respectively. This revised version was published online in August 2006 with corrections to the Cover Date.     

The formation and physicochemical characterization of Al2O3-doped manganese ferrites

Mn/Fe mixed oxide solids doped with Al₂O₃ (0.32-1.27 wt.%) were prepared by impregnation of manganese nitrate with finely powdered ferric oxide, then treated with different amounts of aluminum nitrate. The obtained samples were calcined in air at 700-1000 °C for 6 h. The specific surface area (S_BET) and the catalytic activity of pure and doped precalcined at 700-1000 °C have been measured by using N₂ adsorption isotherms and CO oxidation by O₂. The structure and the phase changes were characterized by DTA and XRD techniques. The obtained results revealed that Mn₂O₃ interacted readily with Fe₂O₃ to produce well-crystallized manganese ferrite (MnFe₂O₄) at temperatures of 800 °C and above. The degree of propagation of this reaction increased by Al₂O₃-doping and also by increasing the heating temperature. The treatment with 1.27 wt.% Al₂O₃ followed by heating at 1000 °C resulted in complete conversion of Mn/Fe oxides into the corresponding ferrite phase. The catalytic activity and S_BET of pure and doped solids were found to decrease, by increasing both the calcination temperature and the amount of Al₂O₃ added, due to the enhanced formation of MnFe₂O₄ phase which is less reactive than the free oxides (Mn₂O₃ and Fe₂O₃). The activation energy of formation (ΔE) of MnFe₂O₄ was determined for pure and doped solids. The promotion effect of aluminum in formation of MnFe₂O₄ was attributed to an effective increase in the mobility of reacting cations.     

Recovery of indium from In2O3 and liquid crystal display powder via a chloride volatilization process using polyvinyl chloride

Indium (In) was recovered from indium oxide (In₂O₃) and liquid crystal display (LCD) powder via a chloride volatilization process using polyvinyl chloride (PVC) as the chlorination agent. The recovery of In from In₂O₃ increased with an increasing molar Cl/In ratio in N₂ and air atmospheres. The degree of In recovery at a Cl/In molar ratio of 11 and a temperature of 350 °C was 98.7% and 96.6%, for N₂ and air, respectively. The In recovery also increased notably with increasing temperature in N₂ atmosphere. In both atmospheres, the In recovery increased with an increasing degradation temperature of PVC. However, the In recovery from LCD powder was lower than that from In₂O₃. For LCD powder, the degree of In recovery at a Cl/In molar ratio of 11 and a temperature of 350 °C was 66.7% and 54.1%, for N₂ and air, respectively.     

Polymorphism in yttrium molybdate Y2Mo3O12

Yttrium molybdate (Y₂Mo₃O₁₂) has been prepared by non-hydrolytic sol–gel chemistry. The phase evolution upon heating was investigated using in situ and ex situ heat treatments combined with powder X-ray diffraction. This method has led to the isolation of two orthorhombic phases with different atomic connectivity. Yttrium adopts 6- and 7-coordinate sites in the Pbcn and Pba2 structures, respectively. Cocrystallization of both phases was observed in a narrow temperature range, suggesting that crystallization kinetics play a major role in phase formation. It was found that the Pba2 phase is the stable polymorph below 550 °C, and converts to Pbcn at higher temperatures.     

The Phase Relations in the System In2O3–TiO2–MgO at 1100 and 1350°C

The phase relations in the system In₂O₃–TiO₂–MgO at 1100 and 1350°C are determined by a classical quenching method. In this system, there are four pseudobinary compounds, In₂TiO₅, MgTi₂O₅ (pseudobrookite type), MgTiO₃ (ilmenite type), and Mg₂TiO₄ (spinel type) at 1100°C. At 1350°C, in addition to these compounds there exist a spinel-type solid solution Mg_2−xIn_2xTi_1−xO₄ (0≤x≤1) and a compound In₆Ti₆MgO₂₂ with lattice constants a=5.9236(7) Å, b=3.3862(4) Å, c=6.3609(7) Å, β=108.15(1)°, and q=0.369, which is isostructural with the monoclinic In₃Ti₂FeO₁₀ in the system In₂O₃–TiO₂–MgO. The relation between the lattice constants of the spinel phase and the composition nearly satisfies Vegard's law. In₆Ti₆MgO₂₂ extends a solid solution range to In₂₀Ti₁₇Mg₃O₆₇ with lattice constants of a=5.9230(5) Å, b=3.3823(3) Å, c=6.3698(6) Å, β=108.10(5)°, and q=0.360. The distributions of constituent cations in the solid solutions are discussed in terms of their ionic radius and site preference effect.     

Investigation on double perovskite Ba4Ca2Ta2O11

The structure, conductivity and water uptake of the oxygen-deficient perovskite-type compound Ba₄Ca₂Ta₂O₁₁ have been investigated. Ba₄Ca₂Ta₂O₁₁ crystallizes in the cryolite structure (cubic, Fm3m SG) with a = 8.4508(2) Å, under dry air. The compound can be partially hydrated up to a maximum water content of approximately 0.52 mol H₂O per mol Ba₄Ca₂Ta₂O₁₁. In moist air, the structure symmetry becomes monoclinic (C2/m) and the temperature dependence of total conductivity shows a different behavior because of changes in transport mechanism. Three regions can be observed as a function of temperature. For the low temperature range 200–400 °C, the protonic conduction is prevailing with an activation energy E_A = 0.85 eV. In the intermediate temperature range (400–600 °C), O²⁻ anionic and protonic conductions are mixed with an activation energy E_A = 0.45 eV and in the third region, for temperatures above 600 °C, O²⁻conduction is prevailing with an activation energy E_A = 0.85 eV.     

Preparation and hydrogen permeation of SrCe0.95Y0.05O3−δ asymmetrical membranes

Asymmetrical thin membranes of SrCe_0.95Y_0.05O_3−δ (SCY) were prepared by a conventional and cost-effective dry pressing method. The substrate consisted of SCY, NiO and soluble starch (SS), and the top layer was the SCY. NiO was used as a pore former and soluble starch was used to control the shrinkage of the substrate to match that of the top layer. Crack-free asymmetrical thin membranes with thicknesses of about 50 μm and grain sizes of 5–10 μm were successfully pressed on to the substrates. Hydrogen permeation fluxes (J_H2) of these thin membranes were measured under different operating conditions. At 950 °C, J_H2 of the 50 μm SCY asymmetrical membrane towards a mixture of 80% H₂/He was as high as 7.6 × 10⁻⁸ mol/cm² s, which was about 7 times higher than that of the symmetrical membranes with a thickness of about 620 μm. The hydrogen permeation properties of SCY asymmetrical membranes were investigated and activation energies for hydrogen permeation fluxes were calculated. The slope of the relationship between the hydrogen permeation fluxes and the thickness of the membranes was −0.72, indicating that permeation in SCY asymmetric membranes was controlled by both bulk diffusion and surface reaction in the range investigated.     

X-ray diffraction and Mössbauer spectroscopy studies of LiFe0.5Ti1.5O4 – A new primitive cubic ordered spinel

LiFe_0.5Ti_1.5O₄ was synthesized by solid-state reaction carried out at 900 °C in flowing argon atmosphere, followed by rapid quenching of the reaction product to room temperature. The compound has been characterized by X-ray powder diffraction (XRD) and ⁵⁷Fe Mössbauer effect spectroscopy (MES). It crystallizes in the space group P4₃32, a = 8.4048(1) Å. Results from Rietveld structural refinement indicated 1:3 cation ordering on the octahedral sites: Li occupies the octahedral (4b) sites, Ti occupies the octahedral (12d) sites, while the tetrahedral (8c) sites have mixed (Fe/Li) occupancy. A small, about 5%, inversion of Fe on the (4b) sites has been detected. The MES data is consistent with cation distribution and oxidation state of Fe, determined from the structural data.The title compound is thermally unstable in air atmosphere. At 800 °C it transforms to a mixture of two Fe³⁺ containing phases – a face centred cubic spinel Li_(1+y)/2Fe_(5−3y)/2Ti_yO₄ and a Li_(z−1)/2Fe_(7−3z)/2Ti_zO₅ – pseudobrookite. The major product of thermal treatment at 1000 °C is a ramsdellite type lithium titanium iron(III) oxide, accompanied by traces of rutile and pseudobrookite.     

Conductivity studies of dense yttrium-doped BaZrO3 sintered at 1325 °C

High-temperature proton conductors have wide applications in the areas of fuel cells, electrolysis and hydrogen separation. Barium zirconate-based materials are of interest due to their good stability and high protonic conductivity. The reported conductivity of these ceramic materials is generally less than 10⁻² S/cm, even at high temperatures. This is not high enough for an electrolyte-supported device to achieve an ASR of less than 0.2 Ω cm² therefore thin film electrolytes are required for successful application. As BaZrO₃-based materials have to be sintered at temperatures as high as 1700 °C, this makes it difficult to find a suitable supporting electrode which will not undergo significant chemical reaction with the BaZrO₃-based electrolyte during fabrication of the required electrode supported electrolyte. In this paper, proton-conducting BaZr_0.8Y_0.2O_2.9 was successfully sintered at 1325 °C with a relative density of 96% via addition of 1 wt% ZnO. Fabrication of electrochemical cells using proton-conducting BaZr_0.8Y_0.2O_2.9 as the electrolyte thus becomes possible. The formula of the 1 wt% ZnO added sample is Ba_0.97Zr_0.77Y_0.19Zn_0.04O_3−δ which exhibits a tetragonal structure with space group P4/mbm (127); a=5.9787(1) Å, c=4.2345(1) Å, V=151.36(1) Å³. It was found that a solid solution was formed for a limited range of Zn doping. Conductivity has been studied as a function of atmosphere (air, dry and wet 5% H₂/Ar) with the changes in bulk and grain boundary on changing atmosphere being monitored as a function of time. The total conductivity of Ba_0.97Zr_0.77Y_0.19Zn_0.04O_3–δ is 1.0×10⁻³ S/cm above 600 °C therefore it may be used as a proton-conducting thin film electrolyte for efficient electrochemical devices at such temperatures. The grain boundary resistance is insignificant at high temperature for the well-sintered sample.     

Fabrication, characterization and magnetic behaviour of alumina-doped zinc ferrite nano-particles

Zinc ferrite nano-powders with a nominal composition of ZnFe₂O₄ were prepared by combustion synthesis using mixture of urea and ammonium nitrate as fuel. The influence of alumina-doping on the structural, morphological and magnetic properties of ZnFe₂O₄ nano-particles was investigated by means of X-ray powder diffraction (XRD), infrared (IR) spectroscopy, scanning and transmission electron microscopy (SEM and TEM) and vibrating sample magnetometer (VSM). XRD and IR analyses confirm the cubic spinel phase of ZnFe₂O₄ nano-particles. The Zn ferrite presented a uniform microstructure with grain size in nano-scale. Alumina-doping brought about a change in the morphology of the as prepared ferrite from sphere-like to regular hexagon. Al₂O₃-treatment led to a decrease in the coercivity (H_c), magnetization (M_s) and magnetic moment (n_B) of the investigated system. The maximum decrease in the values of H_c, M_s and n_B due to the treatment with 1.5 wt% Al₂O₃ attained 13.5, 17.4 and 13.5%, respectively. The observed results can be explained on the basis of particle size and the Fe³⁺ concentration in the octahedral and tetrahedral sites involved in the cubic spinel structure.     

Solid-solid interactions in pure and Li2O-doped manganese and magnesium mixed oxides system

The solid-solid interactions between manganese and magnesium oxides in absence and in presence of small amounts of Li₂O have been investigated. The molar ratios between manganese and magnesium oxides in the form of Mn₂O₃ and MgO were varied between 0.05:1 to 0.5:1. The mixed solids were calcined in air at 400-1000°C. The techniques employed were DTA, XRD and H₂O₂ decomposition at 20-40°C.The results obtained revealed that solid-solid interactions took place between the reacting solids at 600-1000°C yielding magnesium manganates (Mg₂MnO₄, Mg₆MnO₈, MgMnO₄ besides unreacted portions of MgO, Mn₂O₃ and Mn₃O₄). Li₂O-doping (0.75-6 mol%) of the investigated system followed by calcination at 600 and 800°C decreased progressively the intensity of the diffraction lines of Mn₂O₃ (Bixbyite) with subsequent increase in the lattice parameter 'a' of MgO to an extent proportional to the amount of Li₂O added. This finding might suggest that the doping process enhanced the dissolution of Mn₂O₃ in MgO forming solid solution. This treatment led also to the formation of Li₂MnO₃. Furthermore, the doping with 3 and 6 mol% Li₂O conducted at 800°C resulted in the conversion of Mn₂O₃ into Mn₃O₄, a process that took place at 1000°C in absence of Li₂O. The produced Li₂MnO₃ phase remained stable by heating at up to 1000°C. Furthermore, Li₂O doping of the investigated system at 400-1000°C resulted in a progressive measurable increase in the particle size of MgO.The catalytic activity measurements showed that the increase in the molar ratio of Mn₂O₃ in the samples precalcined at 400-800°C was accompanied by a significant increase in the catalytic activity of the treated solids. The maximum increase in the catalytic activity expressed as reaction rate constant measured at 20°C (k _20°C) attained 3.14, 2.67 and 3.25-fold for the solids precalcined at 400, 600 and 800°C, respectively. Li₂O-doping of the samples having the formula 0.1 Mn₂O₃/MgO conducted at 400-600°C brought a progressive significant increase in its catalytic activity. The maximum increase in the value of k _20°C due to Li₂O attained 1.93 and 2.75-fold for the samples preheated at 400 and 600°C, respectively and opposite effect was found for the doped samples preheated at 800°C.This revised version was published online in November 2005 with corrections to the Cover Date.     

Preparation of “pore-fill” type Pd–YSZ–γ-Al2O3 composite membrane supported on α-Al2O3 tube for hydrogen separation

Mesoporous YSZ–γ-Al₂O₃ membranes were coated on α-Al₂O₃ (Ø2 mm) tube by dipping the α-Al₂O₃ support tube into mixed sol consists of nano-size YSZ and bohemite particles followed by drying and calcination at 600 °C. Addition of bohemite in YSZ sol helped a good adhesion and uniform coating of the membrane film onto α-Al₂O₃ support. The quality of the mesoporous YSZ–γ-Al₂O₃ membranes was evaluated by the gas permeability experiments. The number of defects was minimized when the γ-Al₂O₃ content became more than 40%. Addition of γ-Al₂O₃ inhibited the crystal growth of YSZ, sintering shrinkage and distortion stress. Increase of calcination temperature and time results in the increase of pore size and N₂ permeance. A hydrogen perm-selective membrane was prepared by filling palladium into the nano-pores of YSZ–γ-Al₂O₃ layer by vacuum-assisted electroless plating. Crystal growth of palladium was observed by thermal annealing of the membrane at 600 °C for 40 h. The Pd–YSZ–γ-Al₂O₃ composite membrane revealed improved thermal stability allowing long-term operation at elevated temperature (>500 °C). This has been attributed to the improved fracture toughness of YSZ–γ-Al₂O₃ layer and matching of thermal expansion coefficient between palladium and YSZ. Although fracture of the membrane did not occur, decline of H₂ flux was observed when the membrane was exposed in 600 °C. This has been attributed to the agglomeration of palladium particles by crystal growth and dense packing into the pore networks of YSZ–γ-Al₂O₃ by elevation of temperature.