Synthesis and electrical conductivity of La-Sr-X-Mg-O (X = Ti, Zr, Al) perovskite solid solution

Perovskite solid solutions of (La_0.6Sr_0.4)(X_1−yMg_y)O_3−δ (X = Ti, Zr, Al) were prepared by a coprecipitation method using corresponding aqueous solutions and ammonium carbonate solution. The freeze-dried powders were sintered in air at 1000-1500 °C for 1-36 h. Single phase solid solutions were produced in the compositions of (La_0.6Sr_0.4)(Zr_0.6Mg_0.4)O_3−δ and (La_0.6Sr_0.4)(Al_0.9Mg_0.1)O_3−δ where (3 − δ) < 3. For the compositions of X = Ti and Zr for y = 0.1 where (3 − δ) > 3, two phases including perovskite solid solution were produced at 1400-1500 °C. The stability of perovskite solid solution was closely related to the fraction of lattice oxygen atom (3 − δ). A relatively high conductivity was measured for (La_0.6Sr_0.4)(Al_0.9Mg_0.1)O_3−δ (σ = 4.15 × 10⁻⁴ S/cm at 600 °C, activation energy 113.4 kJ/mol). The influence of fraction of oxide ion vacancy on the activation energy was small for δ = 0.1-0.3 of perovskite solid solution.     

Modeling and design of transdermal drug delivery patches containing an external heating device

Process modeling and design concepts were implemented to aid in the manufacturing of heat-enhanced transdermal drug-delivery systems. The simulated prototype consists of a corticosterone-loaded polymer patch applied to the skin and connected to a heating device in which an exothermic reaction occurs. To achieve a desired transdermal flux of 1.2 × 10⁻⁵ mg/cm² h, this contribution focuses on the influences of the (1) initial reaction rate (−r_A0), (2) mass of filler material in the device (m), (3) initial concentration (C₀) of medicament in the patch and (4) overall heat transfer coefficient (U). A regression technique yielded the following results: −r_A0 = 3.000 × 10⁻² kg/m³ s, m = 1.251 × 10⁻⁸ kg, U = 6.124 × 10 J/m² K s and C₀ = 1.966 × 10⁻¹ kg/m³. When m was fixed at 12.5 g, the optimum design required the following specifications: r_A0 = 2.765 × 10⁻² kg/m³ s, U = 1.402 × 10³ J/m² K s and C₀ = 1.941 × 10⁻¹ kg/m³. The priority (S_i) of the input factors (i) in reaching the target delivery rate is: SC₀>S−rA0>Sm>SU.     

Synthesis, characterization and electrochemical properties of a novel triphosphate LiFe2P3O10

A novel lithium iron phosphate has been synthesized by a solution route at moderate temperature. The structure was determined from powder by XRD, HRTEM and SAED experiments. LiFe₂P₃O₁₀ tripolyphosphate crystallizes in the monoclinic system, space group P2₁/m, with lattice constants a = 4.597(7) Å, b = 8.566(4) Å, c = 9.051(4) Å, β = 97.47° and Z = 2. Internal and external vibrational modes (Raman and FTIR) show that the dominant spectral features come from the (P₃O₁₀)⁵⁻ oxo-anions displaying internal and external modes along with the P-O-P bridging modes. Magnetic measurements are consistent with the high-spin configuration of Fe²⁺ cation with an effective magnetic moment 5.51 μ_B. A weak antiferromagnetic ordering is observed below the Néel temperature at T_N = 19 K. Electron paramagnetic resonance spectroscopy confirms this electronic configuration and provides evidence of the presence of a carbonaceous layer onto the particle surface. Electrochemical measurements were carried out in lithium cells with LiPF₆-EC-DEC electrolyte at 25 °C. The material delivered a capacity 70 mAh/g in the voltage range 2.7-3.9 V, close to the theoretical value (72 mAh/g). The resulting cyclic voltammogram indicates a stable structure with a good reversibility with the redox peaks at 3.26 and 3.13 V vs. Li⁰/Li⁺.     

Preparation, characterization and bifunctional electrocatalysis of an inorganic-organic complex with a vanadium-substituted polyoxometalate

An inorganic-organic complex with a vanadium-substituted polyoxometalate 1, formulated as [Cu(phen)₂]₂PVW₁₁O₄₀ was hydrothermally synthesized. Complex 1 crystallizes in the monoclinic P2(1)/c space group with a = 25.9932(12) Å, b = 11.9889(6) Å, c = 23.2672(11) Å, β = 113.6750(10)°, V = 6640.5(6) Å³, R = 0.0312, and Z = 4. Complex 1 is constructed from a Keggin-type anion PVW₁₁O₄₀⁴⁻ coordinated to two [Cu(phen)₂]²⁺ units. One [Cu(phen)₂]²⁺ unit is coordinated to a terminal oxygen and the other [Cu(phen)₂]²⁺ unit is coordinated to a bridging oxygen of the polyoxoanion. Redox activities for both the tungsten and vanadium centers have been observed using cyclic voltammetry performed on 1-bulk modified carbon paste electrode (CPE). It was found that 1 presents good electrocatalytic activities not only for the reduction of IO₃⁻, NO₂⁻, and H₂O₂ but also the oxidation of l-cysteine. Complex 1 also shows intense luminescent properties arising from ligand-to-copper charge transfer and oxygen-to-vanadium charge transfer at room temperature in the solid state.     

Experimental studies of nitrobenzene hydrogenation in a microstructured falling film reactor

Nitrobenzene hydrogenation over palladium catalyst was performed in a microstructured falling film reactor at a range of flowrates (0.5-3 ml/min) and pressure (1-6 bar). Confocal microscopy was used to measure liquid film thickness. Comparison with film thickness prediction equations showed an overprediction of 10-30%. The k_La of this system was estimated to be 3-8 s⁻¹ with interfacial surface area per reaction volume 9000-15000 m²/m³. Conversion was found to be affected by both liquid flowrate and hydrogen pressure, and the reactor operated between the kinetic and mass transfer controlled regimes.     

Electrochemical characterization of a new binary oxide of Mo with Co for O2 evolution in alkaline solution

The α-CoMoO₄ oxide has been obtained by a precipitation method and investigated for the first time for electrocatalysis of the oxygen evolution reaction (oer) in alkaline medium. This method produced the pure crystalline CoMoO4 monoclinic phase with crystallite size ∼46 nm and lattice constants: a = 9.666 Å, b = 8.854 Å, c = 7.755 Å and β = 113.82°. The average particle size (based on area density) and the BET surface area of powders of the oxide were 11.58 μm and 9.4 m² g⁻¹, respectively. Results show that the new oxide is quite active for the oer. Values of the Tafel slope and the reaction order with respect to OH⁻ concentration are observed to be ∼60 mV and ∼1, respectively.     

Local structural analysis of a-SiCx:H films formed by decomposition of tetramethylsilane in microwave discharge flow of Ar

Hydrogenated amorphous silicon carbide (a-SiC_x:H) films were prepared by the decomposition of tetramethylsilane (TMS) with microwave discharge flow of Ar. When radio-frequency (RF) bias voltage (− V_RF) was applied to the substrate, the film hardness increased as (2.39 ± 1.12)-(9.15 ± 0.55) GPa for − V_RF = 0-100 V. The a-SiC_x:H films prepared under various − V_RF conditions were analyzed by the carbon-K near edge X-ray absorption fine structure (NEXAFS), by the elastic recoil detection analysis (ERDA), and by the X-ray photoelectron spectroscopy (XPS). From a quantitative analysis of NEXAFS, the sp²/(sp²+ sp³) ratios of C atoms were evaluated as 67.9 ± 2.0, 55.4 ± 2.7, and 51.7 ± 0.7% for − V_RF = 0, 60, and 100 V, respectively. From ERDA, hydrogen content of the film prepared under the condition of − V_RF = 100 V was found to decrease 28% comparing with that under − V_RF = 0 V. It is suggested that the cause of the increase of the film hardness when applying − V_RF is predominantly the growth of the sp³-hybridized structure of C atoms accompanied by the decrease of hydrogen terminations.     

The ultrasonic electropolymerization of an 5-[o-(4-bromine amyloxy)phenyl]-10,15,20-triphenylporphrin (o-BrPETPP) film electrode and its electrocatalytic properties to dopamine oxidation in aqueous solution

5-[o-(4-Bromine amyloxy)phenyl]-10,15,20-triphenylporphrin (o-BrPETPP) was electropolymerized on a glassy carbon electrode (GCE), and the electrocatalytic properties of the prepared film electrode response to dopamine (DA) oxidation were investigated. A stable o-BrPETPP film was formed on the GCE under ultrasonic irradiation through a potentiodynamic process in 0.1 M H₂SO₄ between −1.1 V and 2.2 V versus a saturated calomel electrode (SCE) at a scan rate of 0.1 V s⁻¹. The film electrode showed high selectivity for DA in the presence of ascorbic acid (AA) and uric acid (UA), and a 6-fold greater sensitivity to DA than that of the bare GCE. In the 0.05 mol L⁻¹ phosphate buffer (pH 6.0), there was a linear relationship between the oxidation current and the concentration of DA solution in the range of 5 × 10⁻⁷ mol L⁻¹ to 3 × 10⁻⁵ mol L⁻¹. The electrode had a detection limit of 6.0 × 10⁻⁸ mol L⁻¹(S/N = 3) when the differential pulse voltammetric (DPV) method was used. In addition, the charge transfer rate constant k = 0.0703 cm s⁻¹, the transfer coefficient α = 0.709, the electron number involved in the rate determining step n_α = 0.952, and the diffusion coefficient D_o = 3.54  10⁻⁵ cm² s⁻¹ were determined. The o-BrPETPP film electrode provides high stability, sensitivity, and selectivity for DA oxidation.     

Assessment of Ba0.5Sr0.5Co1−yFeyO3−δ (y = 0.0-1.0) for prospective application as cathode for IT-SOFCs or oxygen permeating membrane

The influence of iron doping level in Ba_0.5Sr_0.5Co_1−yFe_yO_3−δ (y = 0.0-1.0) (BSCF) oxides on their phase structure, oxygen nonstoichiometry, electrical conductivity, performance as symmetrical cell electrode and oxygen permeating membranes was systematically investigated. A cubic perovskite structure was observed for all the compositions with the presence of iron. The increase of iron doping level resulted in the decrease of the lattice constant, room-temperature oxygen nonstoichiometry, total electrical conductivity, and the increase of area specific resistance (ASR) as cathode with samaria doped ceria electrolyte. However, promising cathode performance with an ASR as low as 0.613 Ω cm² was still obtained at 600 °C for Ba_0.5Sr_0.5FeO_3−δ (BSF). The ceramic membranes composing of BSCF with various iron doping level are all oxygen semi-permeable at elevated temperatures. The increase of iron doping level resulted in the decrease of oxygen permeation flux from JO₂ = 2.28 μmol cm⁻² s⁻¹ (STP) for Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3−δ (BSCF5582) to ∼0.45 μmol cm⁻² s⁻¹ (STP) at 900 °C for BSF (y = 1.0) with the same membrane thickness of 1.1 mm, alongside with the change of the rate-determination step from the oxygen surface exchange to the slow oxygen bulk diffusion. The formation of composite oxide with a proper electronic conducting phase and the thin film technology are important for their prospective application as cathode in IT-SOFCs and oxygen permeating membrane, respectively.     

Electronic transport in Ce0.8Sm0.2O1.9−δ ceramics under reducing conditions

Ce_0.8Sm_0.2O_1.9−δ powders were prepared by a freeze drying method and used to obtain ceramic disks. These samples were used to study the electronic transport properties of this material. A Hebb-Wagner method was used to obtain the electronic conductivity under ion blocking conditions. Typical values of electronic conductivity measured for this material at 800 °C were about 0.37 S m⁻¹ at Po₂=10⁻¹⁶ atm and 0.58 S m⁻¹ at P_O2=10⁻¹⁸ atm. These values are significantly lower than results reported for ceria-based materials with different trivalent additives. A coulometric titration method was used to estimate the charge carrier concentrations, and the mobility of carriers was obtained on combining the results of conductivity and concentration. Typical values of mobility show weak temperature dependence and decrease with increasing oxygen deficiency, suggesting a limiting value of about 0.5×10⁻⁷ m². V⁻¹ s⁻¹ for relatively high δ.     

Direct electrochemistry and electrocatalysis of cytochrome c based on chitosan-room temperature ionic liquid-carbon nanotubes composite

A robust and effective composite film combined the benefits of room temperature ionic liquid (RTIL), chitosan (Chi) and multi-wall carbon nanotubes (MWNTs) was prepared. Cytochrome c (Cyt c) was successfully immobilized on glassy carbon electrode (GCE) surface by entrapping in the composite film. Direct electrochemistry and electrocatalysis of immobilized Cyt c were investigated in detail. A pair of well-defined and quasi-reversible redox peaks of Cyt c was obtained in 0.1 mol L⁻¹ pH 7.0 phosphate buffer solution (PBS), indicating the Chi-RTIL-MWNTs film showed an obvious promotion for the direct electron transfer between Cyt c and the underlying electrode. The immobilized Cyt c exhibited an excellent electrocatalytic activity towards the reduction of H₂O₂. The catalysis current was linear to H₂O₂ concentration in the range of 2.0 × 10⁻⁶ to 2.6 × 10⁻⁴ mol L⁻¹, with a detection limit of 8.0 × 10⁻⁷ mol L⁻¹ (S/N = 3). The apparent Michaelis-Menten constant (K_m) was calculated to be 0.45 ± 0.02 mmol L⁻¹. Moreover, the modified electrode displayed a rapid response (5 s) to H₂O₂, and possessed good stability and reproducibility. Based on the composite film, a third-generation reagentless biosensor could be constructed for the determination of H₂O₂.     

Electrochemical characterization of Co-doped Sr0.8Ce0.2MnO3−δ cathodes on Sm0.2Ce0.8O1.9-electrolyte for intermediate-temperature solid oxide fuel cells

Electrochemical properties of Co-doped Sr_0.8Ce_0.2MnO_3−δ cathode were investigated at the cathode/Sm_0.2Ce_0.8O_1.9 electrolyte interface. The electrochemical impedance spectroscopy was measured under applied cathodic voltages (E = −0.4 to 0 V). At E = 0 V, the area-specific resistance decreased from 2.20 Ω cm² to 0.19 Ω cm² at 700 °C with Co doping. Under the cathodic polarization, the rate determining step of oxygen reduction process was different for both cathodes: the charge transfer for Sr_0.8Ce_0.2MnO_3−δ and the diffusion process for Sr_0.8Ce_0.2Mn_0.8Co_0.2O_3−δ. Besides, the overpotential also decreased from 124 mV to 19 mV at the current density of 0.1 A cm⁻² at 800 °C with Co doping. The improved electrochemical properties of Co-doped Sr_0.8Ce_0.2MnO_3−δ can be ascribed to the formation of more oxygen vacancies and more active sites for oxygen reduction reaction.     

Synthesis and characterization of highly soluble 9,10-diphenyl-substituted poly(2,6-anthracenevinylene)

We report the synthesis and optoelectronic properties of highly soluble poly(9,10-bis(3′,4′-di(2″-ethylhexyloxy))phenyl)-2,6-anthracenevinylene) (HSM-PAV). The key intermediate for the synthesis of HSM-PAV is 2,6-dimethyl-9,10-dibromoanthracene, and the high solubility of HSM-PAV is from the incorporation of lateral 3,4-di(2-ethylhexyloxy)phenyl moieties into the 9,10-positions of anthracene units. The increase of side alkyloxy groups endows HSM-PAV with higher molecular weight (M_n = 3.2 × 10⁴) and better electroluminescence performances (L_max = 590 cd/m², LE_max = 0.27 cd/A) compared with the poly(2,6-anthracenevinylene) with lateral monoalkyoxy moieties (M_n = 1.9 × 10⁴, L_max = 340 cd/m², LE_max = 0.17 cd/A). The electrical conductivity of doped HSM-PAV film with iodine is 5 × 10⁻² S cm⁻¹ that is several order higher than that of doped 9,10-anthracene-based polymers, further demonstrating that linkage position has a dramatic effect on the optoelectronic properties of anthracene-based conjugated polymers.     

The spatial uniformity and electromechanical stability of transparent, conductive films of single walled nanotubes

We have prepared thin films of arc discharge single walled nanotubes by vacuum filtration. For film thicknesses greater than 40 nm, the films are of high optical quality; the optical transmission varies by <2% over the film area when measured with a spatial resolution of 4 μm. However, the films become spatially non-uniform for film thickness below 40 nm. The in-plane DC conductivity correlates with the uniformity, increasing from ∼3800 S/m for a 10 nm thick film to ∼2-2.5 × 10⁵ S/m for films of thickness >40 nm. Conductive atomic force microscopy maps show reasonably uniform current flow out of the plane of the film. For all thicknesses, the optical transmittance scales with film thickness as expected for a thin conducting film with optical conductivity of 1.7 × 10⁴ S/m (λ = 550 nm). For films with t > 40 nm the ratio of DC to optical conductivity was σ_DC/σ_Op = 13.0, leading to values of transmittance and sheet resistance such as T = 80% and R_s = 110 Ω/□ for the t = 40 nm film. Electromechanically, these films were very stable showing conductivity changes of <5% and <2% when cycled over 2000 times in compression and tension respectively.     

Synthesis, microstructure, and photocatalysis of In2O3 hollow particles

Indium oxide (In₂O₃) microspheres with hollow interiors have been prepared by a facile implantation route which enables indium ions released from indium-chloride precursors to implant into nonporous polymeric templates in C₂Cl₄ solvent. The templates are then removed upon calcination at 500 °C in air atmosphere, forming hollow In₂O₃ particles. Specific surface area (0.5-260 m² g⁻¹) and differential pore volume (7 × 10⁻⁹ to 3.8 × 10⁻⁴ m³ g⁻¹ Å⁻¹) of the hollow particles can be tailored by adjusting the precursor concentration. For the hollow In₂O₃ particles with high surface area (260 m² g⁻¹), an enhanced photocatalytic efficiency (up to ∼one-fold increase) against methylene blue (MB) dye is obtained under UV exposure for the aqueous In₂O₃ colloids with a dilute solids concentration of 0.02 wt.%.     

Perovskite and A2MO4-type oxides as new cathode materials for protonic solid oxide fuel cells

Solid state ionic devices based on high-temperature proton conductors can be used for various applications, especially in a new class of fuel cells, the Protonic Ceramic Fuel Cell (SOFC-H⁺). These systems are currently operating at intermediate temperatures (500-600 °C) and one of the major problems is the overpotential at the cathode side. In this context, various perovskite oxides AMO_3 − δ (A = La, Ba, Sr; M = Mn; Fe, Co, Ni) and A₂MO₄-type compounds (A = La, Nd, Pr or Sr; M = Ni) have been investigated. Their properties under moist cathodic atmosphere have been studied. Actually, they are stable and exhibit high electrical conductivity (σ > 100 S cm⁻¹) as well as good electrocatalytic properties towards oxygen reduction.The electrochemical properties of these oxides deposited on the protonic electrolyte BaCe_0.9Y_0.1O_3 − δ have been studied and the Area Specific Resistances have been measured under air/H₂O (3%) atmosphere. The obtained values at 600 °C, especially for Ba_0.5Sr_0.5Fe_0.8Co_0.2O_3 − δ and Pr₂NiO_4 + δ show to be promising cathode materials for Protonic Ceramic Fuel Cell applications.     

Performance of XSCoF (X = Ba, La and Sm) and LSCrX′ (X′ = Mn, Fe and Al) perovskite-structure materials on LSGM electrolyte for IT-SOFC

X_0.5Sr_0.5Co_0.8Fe_0.2O_3−δ (X = Ba, La and Sm) and La0.75Sr0.25Cr0.5X^′0.5O3−δ (X′ = Mn, Fe and Al) mixed ionic-electronic conducting perovskite-based oxides have been tested as SOFC electrode materials on La_0.9Sr_0.1Ga_0.8Mg_0.2O_2.85 (LSGM) electrolytes under different atmospheres (air, oxygen, argon and dry and wet 5% H₂/Ar) and the area-specific resistances (ASR) were compared. Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3−δ (BSCoF) possesses the lowest ASR values in air (0.04 Ω cm² at 1073 K) whilst La_0.75Sr_0.25Cr_0.5Mn_0.5O_3−δ (LSCrM) possesses the lowest ASR values in wet 5% H₂/Ar (0.28 Ω cm² at 1073 K). In addition, fuel cell tests were carried out using wet 5% H₂/Ar as fuel and air as oxidant. The maximum power density (∼123 mW cm⁻²) at 1073 K was reached with the electrolyte-supported system BSCoF/LSGM/LSCrM (∼1.5 mm electrolyte thickness). Furthermore, LSCrX′ materials were used simultaneously as cathode and anode in fuel cell tests and the symmetric system LSCrM/LSGM/LSCrM (∼1.5 mm electrolyte thickness) reached a maximum power density of ∼54 mW cm⁻² at 1073 K.     

Microstructural and electrical characterization of bulk YBa2Cu3O7−δ ceramics

The value of critical current density at 77 K in “zero” applied field (J_c) characterizing the superconducting state for YBa₂Cu₃O_7−δ ceramics is closely related to the microstructure.The interrelationships between the microstructural factors such as pore volume fraction, oxygen content, average grain size, are complex. However, these factors also influence the normal state resistivity measured at room temperature (ρ₃₀₀). We demonstrate how the current carrying cross section influences Jc and ρ₃₀₀ in a similar way. Data, reported for two classes of YBa₂Cu₃O_7−δ: small grain porous ceramics and larger-grain denser ceramics, reveal an approximate linear relation between ρ_300 K and J_c. Extrapolation of this relation to a fully dense small grain YBa₂Cu₃O_7−δ ceramic yields values of ρ₃₀₀ = 0.4 mΩ cm and J_c = 10³ A cm⁻².     

Thermal conductivity and dielectric property of hot-pressing sintered AlN–BN ceramic composites

A study was conducted of the effects of sintering temperature and CaF₂ additives on densification, microstructure, dielectric property and thermal conductivity of AlN–BN composites. Increasing sintering temperature and CaF₂ contents help to improve the densification, thermal conductivity, and purification of the grain boundaries. Thermal conductivity value reached 110 W m⁻¹ K⁻¹ for AlN–BN composites with 3 wt.% CaF₂ and sintered at 1850 °C. Increasing sintering temperature decreases relative dielectric constant and tan δ. The increase in CaF₂ content increases relative dielectric constant and decreases tan δ. Relative dielectric constants values were between 7.29 and 7.64 and dielectric loss tangent values ranged from 6.36 to 7.83 × 10⁻⁴ at 1 MHz.     

Crystal structure of low magnesium-content alite: Application to Rietveld quantitative phase analysis

Five members of tricalcium silicate solid solution, Ca_{3 − x − y}Mg_xAl_y(Si_1 − yAl_y)O₅, have been prepared. T_1, T₃ and M₃ forms have been identified by X-ray powder diffraction, but pure M₁ form was not stabilized. The crystal structure of a sample nominally Ca_2.96Mg_0.03Al_0.01(Si_0.99Al_0.01)O₅ has been studied by a joint Rietveld refinement using strictly monochromatic laboratory X-ray and neutron powder diffraction data, with soft constraints of interatomic distances. The crystal structure of this alite is a T₃ form with a triclinic cell, space group P 1?1­, of dimensions a = 11.6389(2) Å, b = 14.1716(3) Å, c = 13.6434(3) Å, α = 104.982(2)°, β = 94.622(1)°, γ = 90.107(2)° and V/Z = 120.346(6) ų. Laboratory and commercial clinkers were studied by synchrotron X-ray powder diffraction and the Rietveld method. The reported T₃ structure for alite fits properly a variety of laboratory Portland clinkers with low magnesium contents. The alite refined volume(s) (V/Z) is useful to predict the magnesium oxide content of a clinker and the alite-type. Thus, a refined V/Z value between 121.0 and 120.3 Å³ should contain up to ~ 1.0 wt.% of MgO, being T₃ type. If refined C₃S V/Z is smaller than ~ 119.8 Å³ the clinker may contain more than ~ 2.1 wt.% of MgO with alite as M₃. For intermediate magnesium (and sulfur) contents, alites phase coexistence may be detected by using strictly monochromatic laboratory or synchrotron X-ray powder diffraction. However, the application of these results to commercial materials has to be taken cautiously due to the influence of other foreign ions in volume and alite-type.