Methane steam reforming in the absence and presence of H2S over Ce0.8Pr0.2O2 − δ, Ce0.85Sm0.15O2 − δ and Ce0.9Gd0.1O2 − δ SOFCs anode materials

We report here on the activity and stability of low-content praseodymium–, samarium– and gadolinium–cerium oxide catalysts for the steam reforming of methane under water deficient conditions. These materials display different methane reforming activities, and remain free of praseodymium, samarium and gadolinium oxide phases respectively after use in a reaction gas stream composed of 50% CH₄–5% H₂O – (in the absence and presence of 50 or 200 ppm H₂S) – balance He at 740 °C. The results show that Ce_0.8Pr_0.2O_2 − δ, Ce_0.85Sm_0.15O_2 − δ and Ce_0.9Gd_0.1O_2 − δ are effective catalysts for reforming of methane and H₂S in the feed promotes the catalytic activity. Ce_0.8Pr_0.2O_2 − δ appeared to attain the highest activity for methane reforming, a feature that is associated with the ability of praseodymium to undergo a red–ox (Pr^4 +/Pr^3 +) and spreading action in the cerium oxide host structure, possibly resulting in a red–ox relationship between the components.     

Barium-doped Sr2Fe1.5Mo0.5O6-δ perovskite anode materials for protonic ceramic fuel cells for ethane conversion

Protonic ceramic ethane fuel cells fed by hydrocarbon fuels are demonstrated to be effective energy conversion devices. However, their practical application is impeded by a lack of anode materials combining excellent catalytic activity with good chemical stability and anti-carbon deposition properties. In this work, in which Sr₂Fe_1.5Mo_0.5O_6-δ (SFM) double perovskite oxide is used as the matrix framework, catalytic activity toward H₂ and C₂H₆ oxidation is systematically investigated using Ba-doping. It is found that the concentration of the oxygen vacancy is gradually improved with increased Ba content to significantly enhance catalytic activity toward H₂ and C₂H₆ oxidation. From the series studied, Ba_0.6Sr_1.4Fe_1.5Mo_0.5O_6-δ exhibits the highest catalytic activity, while the power densities of the electrolyte-supported Ba_0.6SFM/BaCe_0.7Zr_0.1Y_0.2O_3-δ (BCZY)/La_0.58Sr_0.4Co_0.2Fe_0.8O_3-δ (LSCF)-Sm_0.2Ce_0.8O_2-δ (SDC) single cell reach 205 and 138 mW cm^–2 at 750°C in H₂ and C₂H₆, respectively. The ethane conversion rate of the experimental cell is shown to reach 38.4%, while simultaneously maintaining ethylene selectivity at 95%. Furthermore, the single cell exhibits no significant attenuation during stable operation for 20 h, as well as demonstrating excellent anti-coking performance. The proposed results suggest that Ba_0.6Sr_1.4Fe_1.5Mo_0.5O_6-δ represents a promising anode material for efficient hydrocarbon-related electrochemical conversion to realize the coproduction of ethylene and power in protonic ceramic ethane fuel cells.     

Investigation of dielectric properties and microstructure of sintered 13·2Li2O − 67·6SiO2 − 14.49Al2O3 − 3·3TiO2 − 0.4BaO − 0.97ZnO glass-ceramics

Lithium aluminosilicate (LAS) is an interesting material for the electronics industry. The material has near zero water absorption, low dielectric constant, and low loss tangent. Therefore, this material is interesting for the packaging of radio frequency transmitters used under harsh conditions. In this study, LAS glass powders with different particle sizes were dry pressed. Densification, crystallization, microstructure and dielectric properties were studied during thermal treatments. The highest sintered density (about 97%) has been achieved with milled powder with a d₉₀ of about 6 μm. Investigation of the microstructure reveals that flaky rutile has formed in β-spodumene grain boundaries even though spherical rutile is observed inside of β-spodumene. Glass phase in grain boundaries contain mostly SiO₂, Al₂O₃ and ZnO. Impedance analysis showed that the dielectric constant is influenced by phase transformation and density. The formation of hexagonal LiAlSi₂O₆ increases the dielectric constant while transformation to tetragonal structure decreases the dielectric constant.     

Mesoporous CuO/TixZr1 − xO2 catalysts for low-temperature CO oxidation

Mesoporous CuO/Ti_xZr_1 − xO₂ catalysts were prepared by a surfactant-assisted method, and characterized by N₂ adsorption/desorption, TEM, XPS, in-situ FTIR and H₂-TPR. The catalysts exhibited high specific surface area (S_BET = 241 m²/g) and uniform pore size distribution. XPS and in-situ FTIR displayed that Cu⁺ and Cu²⁺ species coexisted in the catalysts. The CuO/Ti_xZr_1 − xO₂ catalysts presented obviously higher activity in CO oxidation reaction than the CuO/TiO₂ and CuO/ZrO₂ catalysts. Effect of molar ratios of Ti to Zr and calcination temperature on catalytic activity was investigated. The CuO/Ti_0.6Zr_0.4O₂ catalyst calcined at 400 °C exhibited excellent activity with 100% CO conversion at 140 °C.     

Dielectric and Magnetic properties of (1 − x)BiFeO3–xBa0.8Sr0.2TiO3 ceramics

The polycrystalline samples of (1 ? x)BiFeO₃–xBa_0.8Sr_0.2TiO₃ (x = 0, 0.1, 0.2, 0.25, 0.3, 0.4 and x = 1) were prepared by the conventional solid state reaction method. The effect of substitution in BiFeO₃ by Ba_0.8Sr_0.2TiO₃ on the structural, dielectric and magnetic properties was investigated. X-ray diffraction study showed that these compounds crystallized at room temperature in the rhombohedral distorted perovskite structure for x ≤ 0.3 and in cubic one for x = 0.4. As Ba_0.8Sr_0.2TiO₃ content increases, the dielectric permittivity increases. This work suggests also that the Ba_0.8Sr_0.2TiO₃ substitution can enhance the magnetic response at room temperature. A remanent magnetization M_r and a coercive magnetic field H_C of about 0.971 emu/g and 2.616 kOe, respectively were obtained in specimen with composition x = 0.1 at room temperature.     

Crystal structure,mixture behavior,and microwave dielectric properties of novel temperature stable (1 − x)MgMoO4 − xTiO2 composite ceramics

Novel temperature stable MgMoO₄–TiO₂ microwave dielectric ceramics were prepared by a solid state reaction process at low temperature (950 °C). As TiO₂ content increases, the relative permittivity increases while the Q × f value decreases, and the variation mechanisms are proposed, respectively. The temperature coefficient of resonant frequency (τ_f) shifts to the positive direction as TiO₂ is added. The mixture mechanisms of τ_f value for two-phase composite materials are supposed. A near-zero τ_f value (3.2 ppm/°C) is obtained when x = 0.3, with ε_r = 9.13 ± 0.03 and Q × f = 11,990 GHz. The 0.7MgMoO₄–0.3TiO₂ composites are considered to be appropriate as a low temperature co-fired ceramic material for microwave wireless communication applications.     

Microstructure and mechanical properties of Ni/10 mol% Sc2O3–1 mol% CeO2–ZrO2 cermet anode for solid oxide fuel cells

The mechanical properties of anode materials play an important role in the reliability and durability of solid oxide fuel cells operating at high temperatures in a reducing environment. In this paper, we produced the results of the mechanical properties investigation of Ni/10 mol% Sc₂O₃–1 mol% CeO₂–ZrO₂ cermet anodes. Young's modulus as well as strength and fracture toughness of non-reduced and reduced anodes has been measured, both at room and at high temperatures. High temperature experiments were performed in the reducing environment of forming gas. It is shown that while at 700 °C and 800 °C, the anode specimens exhibited purely elastic deformation and brittle fracture, a brittle-to-ductile transition occurred for heating above 800 °C and the anode deformed plastically at 900 °C. Fractography of the anode specimens were performed to identify the fracture modes of anodes tested at different temperatures.     

New high Q microwave dielectric ceramics with rock salt structures: (1 − x)Li2TiO3 + xMgO system (0 ≤ x ≤ 0.5)

The structural evolution and microwave dielectric properties of (1 ? x)Li₂TiO₃ + xMgO system (0 ≤ x ≤ 0.5) have been investigated in this paper. The ordering degree decreased with the increase of MgO content. The microcracks and cleavage on (0 0 1) due to the weak Li–O bonds disappeared with the increase of MgO content. The dielectric constant and temperature coefficient of resonant frequency decreased with the increase of MgO content. The Q × f value increased with x up to x = 0.2 and then decreases with the further increase of x. An excellent combined microwave dielectric properties could be obtained when x = 0.24, ?_r = 19.2, Q × f = 106,226 GHz and τ_f = 3.56 ppm/°C.     

Enhanced activity of MnxW0.05Ti0.95 − xO2 − δ for selective catalytic reduction of NOx with ammonia by self-propagating high-temperature synthesis

A series of TiO₂ supported MnWO_x catalysts Mn_xW_0.05Ti_0.95 − xO_2 − δ (x = 0.05, 0.1, 0.15) were synthesized by solution combustion method. The Mn_0.10W_0.05Ti_0.85O_2 − δ catalyst showed highest activity in NH₃-SCR reaction within a broad temperature range of 200 °C–400 °C. XRD and TEM results indicate that the active Mn and W species are highly dispersed over TiO₂ support in the form of nanoparticles (4–7 nm). The TEM and H₂-TPR results also suggest that a MnWO_x phase has been formed on the TiO₂, which is beneficial for the activity of the Mn_xW_0.05Ti_0.95 − xO_2 − δ catalysts in the high temperature range of 280 °C–400 °C.     

Reduced graphene oxide anchored with δ-MnO2 nanoscrolls as anode materials for enhanced Li-ion storage

We developed a one-pot in situ synthesis procedure to form nanocomposite of reduced graphene oxide (RGO) sheets anchored with 1D δ-MnO₂ nanoscrolls for Li-ion batteries. The as-prepared products were characterized by X-ray diffraction (XRD), Raman spectra, X-ray photoelectron spectroscopy (XPS), field emission scanning electron microscope (FESEM) and transmission electron microscope (TEM). The electrochemical performance of the δ-MnO₂ nanoscrolls/RGO composite was measured by galvanostatic charge/discharge cycling and electrochemical impedance spectroscopy. The results show that the δ-MnO₂ nanoscrolls/RGO composite displays superior Li-ion battery performance with large reversible capacity and high rate capability. The first discharge and charge capacities are 1520 and 810 mAh g⁻¹, respectively. After 50 cycles, the reversible discharge capacity is still maintained at 528 mAh g⁻¹ at the current density of 100 mAh g⁻¹. The excellent electrochemical performance is attributed to the unique nanostructure of the δ-MnO₂ nanoscrolls/RGO composite, the high capacity of MnO₂ and superior electrical conductivity of RGO.     

Composites of V2O3–ordered mesoporous carbon as anode materials for lithium-ion batteries

The composites of V₂O₃–ordered mesoporous carbon (V₂O₃–OMC) were synthesized and used as anode materials for Li-ion intercalation. These materials exhibited large reversible capacity, high rate performance and excellent cycling stability. For instance, a reversible capacity of V₂O₃–OMC composites was 536 mA h g⁻¹ after 180 cycles at a current density of 0.1 A g⁻¹. The high electrochemical performance of the V₂O₃–OMC composites is attributed to the anchoring of nanoparticles on mesoporous carbon for improving the electrochemical active of V₂O₃ particles for energy storage applications in high performance lithium-ion batteries.     

Statistical design of experiments for evaluation of Y–Zr–Ti oxides as anode materials in solid oxide fuel cells

Abstract

Mixed conducting anode materials for solid oxide fuel cells are desirable in order to extend the electron transfer reaction zone for fuel gas conversion and to minimise the nickel content for achieving a redox stable anode. Partial substitution by titania in yttria stabilised zirconia (YSZ) is known to increase the electronic conductivity in reducing atmospheres. Nine different compositions were selected from the quasi ternary phase diagram according to principles used in statistical design of experiments covering the whole stoichiometric regime relevant for ionic applications. The dc electrical conductivity values increase strongly with high Ti contents under reducing (Ar–4%H₂) conditions, whereas they decrease continuously with increasing Ti content under oxidising conditions (air). The results clearly show that the chosen screening process for materials selection can considerably reduce the number of samples. For solid oxide fuel cell anodes, the compositions in the YO_1.5–ZrO₂–TiO₂ system should be restricted to low Ti contents.     

The dehydrogenation of ethylbenzene with CO2 over CexZr1 − xO2 solid solutions

With the purpose of changing the lattice structure of CeO₂ and improving the transmission capacity of lattice oxygen, Ce_xZr_1 − xO₂ solid solutions with different Zr proportions were synthesized using a hydrothermal method and applied in oxidative dehydrogenation of ethylbenzene to styrene with CO₂ at 550 °C. The Ce_0.5Zr_0.5O₂ showed the highest activity with an ethylbenzene conversion of 55% and styrene selectivity above 86%. Analytical characterization showed that the lattice oxygen mobile capacity of Ce_xZr_1 − xO₂ solid solutions was enhanced, corresponding to the order as Ce_0.3Zr_0.7O₂ > Ce_0.5Zr_0.5O₂ > Ce_0.7Zr_0.3O₂ > CeO₂. The oxygen storage/release capacity, higher surface area and pore distribution of Ce–Zr mixed oxides play important roles in the activity of ethylbenzene dehydrogenation to styrene with CO₂.     

α-Fe2O3@CNSs nanocomposites as superior anode materials for lithium-ion batteries

The nanocomposite of hematite@carbon nanosprings (α-Fe₂O₃@CNSs) was synthesized by simple precipitation and following heat treatment, in which the amount of α-Fe₂O₃ can be easily controlled by changing the synthesis conditions. Thermogravimetric analysis (TGA), X-ray diffraction (XRD), scanning electronic microscopy (SEM), Brunau–Emmertt–Teller (BET), and X-ray photoelectron spectroscopy (XPS) were employed to characterize the as-synthesized nanocomposite. When applied as anode in Li-ion batteries (LIBs), the effect of α-Fe₂O₃/CNSs weight ratio on electrochemical performance of α-Fe₂O₃@CNSs nanocomposite has been researched. Enhancing the amount of α-Fe₂O₃ in nanocomposite would make the increase of specific capacity, but led to the degradation of cyclic stability and rate capability. The electrode of S-FeC (with weight ratio of CNSs/α-Fe₂O₃ about 4:1) could deliver a charge capacity of 527.6 mAh g⁻¹at 0.2 C with excellent cyclability (96.9% capacity retention after 50 cycles), and retained 343.3 mAh g⁻¹even at the rate of 5.0 C. In comparison with pure CNSs and α-Fe₂O₃, the improved cycling performance, specific capacity and rate capability of S-FeC should be mainly attributed to the combined effects of uniformly dispersed nanosized α-Fe₂O₃ particles and the highly strong network of CNSs.     

Dispersion and valence state of MnO2/Ce(1 − x)ZrxO2–TiO2 for low temperature NH3-SCR

Zr-doped MnO_x/CeO₂–TiO₂ for high temperature stability was investigated in terms of its dispersion and oxidation state. Aggregation of cerium oxide was observed in MnO_x/CeO₂–TiO₂, but the Zr-doped catalyst was well dispersed. An increase of the Mn^4 +/Mn^3 + ratio was confirmed with a Zr addition through valence state analysis. De-NOx efficiency of the catalyst was increased to 40–45% by Zr addition at low temperature (150–200 °C). The substitution of Zr led the catalyst to improve the de-NOx efficiency, with a high dispersion and MnO₂ ratio.     

Ultra-low temperature sintered (1–x)BaV2O6-xLiF ceramics for ULTCC and 5 G millimeter-wave antenna applications

(1–x)BaV₂O₆-xLiF (x = 0.025, 0.05, 0.10, 0.15) ceramics with an ultra-low sintering temperature of 475 °C were synthesized using the standard solid-state reaction method. The ceramics demonstrated a remarkable enhancement in the quality factor (Qf), reaching a maximum value of 16,800 GHz at x = 0.10, which is 5.6 times higher than that of pure BaV₂O₆ ceramics obtained in this work. A near-zero temperature coefficient of resonant frequency (τ_f = 1.44 ppm/°C) was simultaneously achieved, together with a dielectric constant ε_r of 11.54. Additionally, the chemical compatibility between the present ceramics and the Al electrode was confirmed. Moreover, a millimeter-wave antenna with an excellent S₁₁ value of −50.3 dB, and a large bandwidth of 3.44 GHz was fabricated using the 0.9BaV₂O₆-0.1LiF ceramic as the dielectric resonator. These results highlight the potential application prospects of (1–x)BaV₂O₆-xLiF ceramics in the ultra-low temperature co-fired ceramic technology and 5 G millimeter-wave antennas.     

Structure stability and microwave dielectric properties of double perovskite ceramics – Ba2Mg1−xCaxWO6 (0.0 ≤ x ≤ 0.15)

The structure stability of double perovskite ceramics – Ba₂Mg_1?xCa_xWO₆ (0.0 ≤ x ≤ 0.15) has been studied by X-ray powder diffraction (XRD), scanning electron microscopy (SEM) and Raman spectrometry in this paper. The microwave dielectric properties of the ceramics were studied with a network analyzer at the frequency of about 8–11 GHz. The results show that small amount of Ca substitution for Mg increases the Mg/CaO bond strength, and hence the stability of the double perovskite. But it cannot completely suppress the decomposition of Ba₂Mg_1?xCa_xWO₆ at high temperature. Although space group Fm?3m is adopted for all compositions, nonrandom distribution of Ca²⁺ and Mg²⁺ on 4b-site within the short range scale is observed due to their large cation size difference. Small level doping of Ca (x ≤ 0.1) increases the dielectric permittivity monotonically, but does not affect the Q × f value greatly. As expected, the substitution of Ca tuned the temperature coefficient of resonant frequency (τ_f value) from negative to positive value. Excellent combined microwave dielectric properties with ?_r = 20.8, Q × f = 120,729 GHz, and τ_f = 0 ppm/°C could be obtained for x = 0.1 composition. However the Q × f value degrades considerably when the sample was stored under ambient conditions for a long time.     

Characterization of Ba0.5Sr0.5M1−xFexO3−δ (M = Co and Cu) perovskite oxide cathode materials for intermediate temperature solid oxide fuel cells

Ba_0.5Sr_0.5Co_1?xFe_xO_3?δ (x = 0.2, 0.6, and 0.8) and Ba_0.5Sr_0.5Cu_1?xFe_xO_3?δ (x = 0.6 and 0.8) perovskite oxides have been investigated as cathode materials for intermediate temperature solid oxide fuel cells. All the samples synthesized by a citrate–EDTA complexing method were single-phase cubic perovskite solid solutions. Then, the thermal expansion coefficient, electrical conductivities, the oxygen vacancy concentrations, the polarization resistances (R_p), and the power densities were measured. An increase in the Co content resulted in a decrease in the polarization resistance, the electrical conductivities at low temperatures, and the inflection point of the thermal expansion coefficient, but it led to an increase in the electrical conductivities at high temperatures, the oxygen vacancy concentrations, and the maximum power densities. The Cu-based system has similar behavior to the Co-based system; yet, in terms of the electrical conductivities, high Cu content gave a better result than low content for the entire range of temperatures.     

Thermal expansion and thermal conductivity of SmxZr1−xO2−x/2 (0.1 ≤ x ≤ 0.5) ceramics

A study was conducted of the effect of additions of samarium oxide on the thermal expansion and thermal conductivity of zirconium oxide for thermal barrier coatings. Sm_xZr_1?xO_2?x/2 (0.1 ≤ x ≤ 0.5) ceramic powders synthesized with a chemical-coprecipitation and calcination method were sintered at 1873 K for 15 h. Structures of the synthesized powders and sintered ceramics were identified by X-ray diffractometer. The morphologies of ceramic powders were observed by transmission electron microscope. The thermal expansion coefficients and thermal diffusion coefficients of Sm_xZr_1?xO_2?x/2 ceramics were studied with a high-temperature dilatometer and a laser flash diffusivity technique from room temperature to 1673 K. The thermal conductivity was calculated from thermal diffusivity, density and specific heat of bulk ceramics. Sm_0.1Zr_0.9O_1.95 ceramics consists of both monoclinic and tetragonal structures. However, Sm_0.2Zr_0.8O_1.9 and Sm_0.3Zr_0.7O_1.85 ceramics only exhibit a defect fluorite structure. Sm_0.4Zr_0.6O_1.8 and Sm_0.5Zr_0.5O_1.75 ceramics have a pyrochlore-type lattice. With the increase of Sm₂O₃ content, the linear thermal expansion of Sm_xZr_1?xO_2?x/2 ceramics increases except for Sm_0.1Zr_0.9O_1.95. The thermal conductivities of Sm_xZr_1?xO_2?x/2 ceramics ranged from 1.41 at 873 K to 1.86 W m^?1 K^?1 at room temperature in a test temperature range of room temperature to 1673 K, and the results can be explained by phonon scattering mechanism.     

Nanofiber-based LaxSr1−xTiO3-GdyCe1−yO2−δ composite anode for solid oxide fuel cells

La_xSr_1−xTiO₃ (LST) nanofibers with pure perovskite structure, smooth surface, uniform diameter and length are prepared by electrospinning technique, and applied as scaffolds of La_xSr_1−xTiO₃-Gd_yCe_1−yO_2−δ (LST-GDC) composite anodes for SOFCs. The optimal La doping ratio of LST scaffold has been found to be 0.4, and 0.2 the optimal Gd doping ratio of GDC impregnation phase. The LST:GDC optimal mass ratio of nanofiber-based composite anode has been found to be 1:1.5481, and the composite anode (electrolyte is yttria-stabilized zirconia) to show low interfacial polarization resistances of 0.7309, 0.4688 and 0.2966 Ω cm² at 800, 850 and 900 °C, respectively. In addition, the microstructure of LST materials has been found to plays an important role on the electrochemical performance of the anodes, and the LST nanofiber scaffolds to show the higher porosity leading to a larger triple phase (ionic conduction phase, electronic conduction phase and gas phase) boundary (TPB) area for the composite anodes.