A mixed-conducting BaPr0.8In0.2O3 − δ cathode for proton-conducting solid oxide fuel cells

A mixed ionic and electronic conductor, BaPr_0.8In_0.2O_3 − δ (BPI), was synthesized and examined as a cathode material for proton-conducting solid oxide fuel cells (H-SOFCs). X-ray diffraction analysis revealed that BPI had a perovskite structure and showed satisfactory tolerance to CO₂ and H₂O and good chemical compatibility with BaZr_0.1Ce_0.7Y_0.1 Yb_0.1O_3 − δ (BZCYYb) electrolyte. Test cells with a single-phase BPI cathode exhibited excellent electrochemical performances, demonstrating a peak power density of ~ 688 mW cm^− 2 at 750 °C. Furthermore, the cells with a BPI cathode showed very stable power output at a cell voltage of 0.7 V at 600 °C over 100 h, suggesting that BPI is a promising alternative cathode for H-SOFCs.     

Crystal structure,chemical stability and electrical properties of Sr2MnNbO6 − δ, Sr2Cr0.5Mn0.5NbO6 − δ and Sr2CuNbO6 − δ perovskites

Journal of Solid State Electrochemistry - The 3d-cation-substituted perovskites Sr2MnNbO6 − δ, Sr2Cr0.5Mn0.5NbO6 − δ and...     

Synthesis,characterization and thermochemistry of Cs(ASP) · nH2O (n = 0, 1)

New compounds of aspartic acid Cs(ASP) · nH₂O (n = 0, 1) have been synthesized and characterized by XRD, IR and Raman spectroscopy as well as TG. The structural formula of this new compound was Cs(ASP) · nH₂O (n = 0, 1). The enthalpy of solution of Cs(ASP) · nH₂O (n = 0, 1) in water were determined. With the incorporation of the standard molar enthalpies of formation of CsOH(aq) and ASP(s), the standard molar enthalpy of formation of −(1202.9 ± 0.2) kJ · mol⁻¹ of Cs(ASP) and −(1490.7 ± 0.2) kJ · mol⁻¹ of Cs(ASP) · H₂O were obtained.     

Measurements of the critical parameters for {xNH3 + (1 − x)H2O} with x = (0.9098, 0.7757, 0.6808)

Measurements of the critical parameters for {xNH₃ + (1 ? x)H₂O} with x = (0.9098, 0.7757, 0.6808) were carried out by using a metal-bellows variable volumometer with an optical cell. The expanded uncertainties (k = 2) in temperature, pressure, density, and composition measurements have been estimated to be less than 3.2 mK, 3.2 kPa, 0.3 kg · m^?3, and 8.8 · 10^?4, respectively. In each mole fraction, the critical temperature T_c was first determined on the basis of the intensity of the critical opalescence. The critical pressure p_c and critical density ρ_c were then determined as the point at which the meniscus disappears on the isotherm at T = T_c. The expanded uncertainties (k = 2) in the present critical parameters have also been estimated. Comparisons of the present values with the literature data as well as the calculated values afforded using the equation of state are also presented.     

Thermodynamic study of (alkyl esters + α,ω-alkyl dihalides) III. HmEandVmE for 20 binary mixtures {xCu − 1H2u − 1CO2C4H9 + (1 − x)α,ω-ClCH2(CH2)v − 2CH2Cl}, where u = 1 to 4, α = 1 and v = ω = 2 to 6

In this article, the experimental data of excess molar enthalpies $H_{\mathrm{m}}^{\mathrm{E}}$ and excess molar volumes $V_{\mathrm{m}}^{\mathrm{E}}$ are presented for a set of 20 binary mixtures comprised of the first four butyl alkanoates (methanoate to butanoate) and five α,ω-dichloroalkanes (1,2-dichloroethane to 1,6-dichlorohexane), obtained at atmospheric pressure and at a temperature of 298.15 K. The results indicate the existence of specific interactions between both kinds of compounds resulting in exothermic processes for most mixtures, except for those containing butyl methanoate which give rise to net endo/exothermic effects. The $V_{\mathrm{m}}^{\mathrm{E}}$ are positive for mixtures of (butyl esters + 1,2-dichloroethane or 1,3-dichloropropane) and negative for the remaining ones. The change in $H_{\mathrm{m}}^{\mathrm{E}}$ with the dichloroethane chain length for a same ester is regular although the $V_{\mathrm{m}}^{\mathrm{E}}$ presents an irregular variation. It can, therefore, be deuced from this that the mixing process involves both effects, exothermic/endothermic and expansion/contraction, simultaneously. The behaviour of the mixtures is interpreted on the basis of the results observed and attributed to different effects taking place among the molecules studied.To improve application of the UNIFAC model using the version of Dang and Tassios, average values were recalculated again for parameters of the ester/chloride interaction, distinguishing, during its application, the functional group of the acid part of the ester. In spite of this, the model does not adequately reproduce the systems’ behaviour.     

LaNi1 − x Cu x O3 (x = 0.05, 0.10, 0.30) coated electrodes for oxygen evolution in alkaline medium

LaNi_1???x Cu _x O₃ (x?=?0.05, 0.10, 0.30) coated electrodes were prepared by brush painting using Ni foam substrates in order to increase its active surface area. For comparison, coatings with x?=?0.05 were also prepared using vitreous carbon substrates. Cyclic voltammetry was used to evaluate the coating roughness (R _f). Values between 5,145?±?148 and 6,334?±?277 were obtained, depending on the x value, for the coatings on Ni foam. These results show that the electrodes prepared with LaNi_1???x Cu _x O₃ powder, obtained at 600 °C, lead to a big increase on the oxide electrode roughness when compared with LaNiO₃ electrodes prepared by a similar method. Much lower values were obtained for the coatings on vitreous carbon indicating that the substrate nature is also a key factor for the preparation of high surface area electrodes. The calculated kinetic parameters for the oxygen evolution reaction (OER) show that the partial replacement of Ni by Cu has no beneficial effect on the intrinsic catalytic activity of the coatings. On the other hand, a big increase on the active area is observed even for small amounts of Cu (x?=?0.05), leading to a better overall OER performance for the LaNi_0.95Cu_0.05O₃ coating on Ni foam. For this composition, the activity is dominated by geometric effects.     

Synthesis and structural mechanisms of the 2201-type ferrites and polytypes: Fe2(Sr2 − xAx)FeO6.5 − δ/2 (A = Ba,La, Tl,Pb and Bi)

The Fe₂(Sr_2 ? xA_x)FeO_6.5 ? δ/2 systems have been investigated, by doping the iron rich 2201-type parent structure with Ba²⁺, La³⁺ and 5d¹⁰ post-transition cations. The syntheses have been carried out up to the limit of the 2201-type solid solutions, in order to test the role of the double iron layer Fe₂O_2.5 ? δ/2. The localisation of the charge carriers in these compounds is consistent with their strong antiferro-magnetism. The investigation was then carried out in the transition part of the diagram up to the formation of stable phases. The study of structural mechanisms was carried using high resolution electron microscopy (transmission and scanning transmission), electron diffraction and energy dispersive spectroscopy. Different non-stoichiometry mechanisms are observed, depending on the electronic structure and chemical properties of the doping elements. The specific behavior of the modulated double iron layer is discussed.     

Doping effects on mixed-phase crystalline perovskite AxSr1−xFeO3−δ (A = Pr,Sm; 0 ≤ x ≤ 0.8) nanoparticles and their application for photodegradation of rhodamine B

Research on Chemical Intermediates - A series of doped perovskite AxSr1?xFeO3?δ (A?=?Pr, Sm; 0?≤?x?≤?0.8) nanoparticles were...     

The liquid–liquid coexistence curves of {x dimethyl adipate + (1 − x) n-hexane} and {x dimethyl adipate + (1 − x) n-heptane} in the critical region

The liquid–liquid coexistence curves for (dimethyl adipate + n-hexane), (dimethyl adipate + n-heptane) have been measured, from which the critical amplitudes and the critical exponents are deduced. The critical exponent β corresponding to the coexistence curves are consistent with the 3D-Ising value. The experimental results have also been analyzed to determine the critical amplitudes of Wegner-correction terms when β and Δ are fixed at their theoretical values, and to examine the asymmetry of the diameters for the coexistence curves.     

The liquid–liquid coexistence curves of {x dimethyl adipate + (1 − x) n-octane} and {x dimethyl adipate + (1 − x) n-nonane} in the critical region

The liquid–liquid coexistence curves of (dimethyl adipate + n-octane) and (dimethyl adipate + n-nonane) have been determined within about 10 K from the critical temperatures, from which the critical amplitudes and the critical exponents are deduced. The critical exponents corresponding to the coexistence curve β are consistent with the 3D-Ising values. The experimental results have been analyzed to determine Wegner-correction terms and to discuss the asymmetric behaviour of the diameters of the coexistence curves by the complete scaling theory. Molar mass-dependences of the critical amplitude and the critical volume fraction have been shown to be consistent with the theoretical prediction.     

Cation distribution in MgxZn1 − x(HCOO)2·2H2O mixed crystals: X-ray diffraction and double matrix infrared spectroscopy

The metal ion distributions at the two metal sites (hexaformate-coordinated Me1 sites and mixed-coordinated Me2 sites) in the title mixed crystals as determined by single crystal X-ray diffraction and double matrix infrared spectroscopic methods are presented and discussed. The mixed formates are isostructural with the end compounds (space group P2₁/c). The local metal ion concentrations as a function of the total metal ion concentrations exhibit a clear preference of Zn²⁺ ions to Me1 sites and the Mg²⁺ ions to Me2 sites.The analysis of the infrared spectra reveals that the spectral regions 2300–2500 cm⁻¹ (ν_OD of matrix-isolated HDO molecules) and 1300–1400 cm⁻¹ (symmetric COO stretching (ν₂) and bending CH (ν₅) modes) are mostly sensitive to the metal ion environment. The inclusion of Mg²⁺ and Zn²⁺ in the structures of Zn(HCOO)₂·2H₂O and Mg(HCOO)₂·2H₂O, respectively, leads to an appearance of new infrared bands corresponding to ν_OD of HDO molecules bonded to the incorporated ions (i.e. new hydrogen bonding systems MgOH₂⋯OCHOZn and ZnOH₂⋯OCHOMg are formed in the mixed formates). The respective new bands are observed at small concentrations of included Mg²⁺ ions (about 5 mol%, x = 0.05) and at considerably higher concentrations of included Zn²⁺ ions (about 30 mol%, x = 0.7). Contrarily, the ν₂ and ν₅ modes caused by the incorporated cations bonded to formate ions occur at x ≥ 0.3 and x ≤ 0.85 (Mg²⁺ ions in Zn(HCOO)₂·2H₂O and Zn²⁺ ions in Mg(HCOO)₂·2H₂O, respectively). Thus, the infrared spectroscopy experiments confirm the single crystal X-ray measurements that the Mg²⁺ ions are localized predominantly at Me2 sites and the Zn²⁺ ions at Me1 sites in the title mixed crystals. The pronounced preference of the Mg²⁺ ions to Me2 sites is owing to the strong affinity of these ions to water molecules.     

(Solid + liquid) equilibria for the ternary system (CsBr + LnBr3 + H2O) (Ln = Pr,Nd, Sm) at T = 298.2 K and atmospheric pressure,thermal and fluorescent properties of Cs2LnBr5·10H2O

The (solid + liquid) phase equilibria of the ternary systems (CsBr + LnBr₃ + H₂O) (Ln = Pr, Nd, Sm) at T = 298.2 K were studied by the isothermal solubility method. The solid phases formed in the systems were determined by the Schreinemakers wet residues technique, and the corresponding phase diagrams were constructed based on the measured data. Each of the phase diagrams, with two invariant points, three univariant curves, and three crystallization regions corresponding to CsBr, Cs₂LnBr₅·10H₂O and LnBr₃·nH₂O (n = 6, 7), respectively, belongs to the same category. The new solid phase compounds Cs₂LnBr₅·10H₂O are incongruently soluble in water, and they were characterized by chemical analysis, XRD and TG-DTG techniques. The standard molar enthalpies of solution of Cs₂PrBr₅·10H₂O, Cs₂NdBr₅·10H₂O and Cs₂SmBr₅·10H₂O in water were measured to be (52.49 ± 0.48) kJ · mol⁻¹, (49.64 ± 0.49) kJ · mol⁻¹ and (50.17 ± 0.48) kJ · mol⁻¹ by microcalorimetry under the condition of infinite dilution, respectively, and their standard molar enthalpies of formation were determined as being −(4739.7 ± 1.4) kJ · mol⁻¹, −(4728.4 ± 1.4) kJ · mol⁻¹ and −(4724.4 ± 1.4) kJ · mol⁻¹, respectively. The fluorescence excitation and emission spectra of Cs₂PrBr₅·10H₂O, Cs₂NdBr₅·10H₂O and Cs₂SmBr₅·10H₂O were measured. The results show that the upconversion spectra of the three new solid phase compounds all exhibit a peak at 524 nm when excited at 785 nm.     

Magnetic and optical investigation of 40SiO2·30Na2O·1Al2O3·(29 − x)B2O3·xFe2O3 glass matrix

Samples of 40SiO₂·30Na₂O·1Al₂O₃·(29 − x)B₂O₃·xFe₂O₃ (mol%), with 0.0 ≤ x ≤ 17.5, were prepared by the fusion method and investigated by electron paramagnetic resonance (EPR), optical absorption (OA) and Mössbauer spectroscopy (MS). The EPR spectra of the as-synthesized samples exhibit two well-defined EPR signals around g = 4.27 and g = 2.01 and a visible EPR shoulder around g = 6.4, assigned to isolated Fe³⁺ ion complexes (g = 4.27 and g = 6.4) and Fe³⁺-based clusters (g = 2.01). Analyses of both EPR line intensity and line width support the model picture of Fe³⁺-based clusters built in from two sources of isolated ions, namely Fe²⁺ and Fe³⁺; the ferrous ion being used to build in iron-based clusters at lower x-content (below about x = 2.5%) whereas the ferric ion is used to build in iron-based clusters at higher x-content (above about x = 2.5%). The presence of Fe²⁺ ions incorporated within the glass template is supported by OA data with a strong band around 1100 nm due to the spin-allowed ⁵E_g–⁵T_2g transition in an octahedral coordination with oxygen. Additionally, Mössbauer data (isomer shift and quadrupole splitting) confirm incorporation of both Fe²⁺ and Fe³⁺ ions within the template, more likely in tetrahedral-like environments. We hypothesize that ferrous ions are incorporated within the glass template as FeO₄ complex resulting from replacing silicon in non-bridging oxygen (SiO₃O⁻) sites whereas ferric ions are incorporated as FeO₄ complex resulting from replacing silicon in bridging-like oxygen silicate groups (SiO₄).