Preparation and characterization of sulfated zirconia (SO4/ZrO2)/Nafion composite membranes for PEMFC operation at high temperature/low humidity

Fine particle superacidic sulfated zirconia (SO₄²⁻/ZrO₂, S-ZrO₂) was synthesized by ameliorated method, and composite membranes with different S-ZrO₂ contents were prepared by a recasting procedure from a suspension of S-ZrO₂ powder and Nafion solution. The physico-chemical properties of the membranes were studied by ion exchange capacity (IEC) and liquid water uptake measurements, scanning electron microscopy (SEM) and X-ray diffraction (XRD) analysis, thermogravimetry–mass spectrometry (TG–MS) and Fourier transform infrared (FT-IR) spectroscopy. The results showed that the IEC of composite membrane increased with the content of S-ZrO₂, S-ZrO₂ was compatible with the Nafion matrix, the incorporation of the S-ZrO₂ could increase the crystallinity and also improve the initial degradation temperature of the composite membrane. The performance of single cell was the best when the S-ZrO₂ content was 15 wt.%, and achieved 1.35 W/cm² at 80 °C and 0.99 W/cm² at 120 °C based on H₂/O₂ and at a pressure of 2 atm, the performance of the single cell with optimized S-ZrO₂ was far more than that of the Nafion at the same condition (e.g. 1.28 W/cm² at 80 °C, 0.75 W/cm² at 120 °C). The 15 wt.% S-ZrO₂/Nafion composite membrane showed lower fuel cell internal resistance than Nafion membranes at high temperature and low relative humidity (RH).     

Spectroscopic studies of polymorphs of AlPO4 and SiO2

IR spectra of basic polymorphic forms of AlPO₄, measured at different temperatures, are presented. Diffuse reflectance spectroscopy has been used for high temperature measurements. According to the crystal structures of different AlPO₄ forms by means of factor group analysis, a number of modes and their activities have been determined. An attempt to assign bands to specific normal vibrational modes has been undertaken, comparing spectra of subsequent forms of AlPO₄ with each other. The obtained results have been discussed with regard to data referring to various isomorphous polymorphic forms of SiO₂, comparing, respectively, cristobalite with phosphocristobalite, berlinite with quartz, and phosphotridymite with tridymite (M. Handke and W. Mozgawa, Vib. Spectrosc. 5 (1993) 75; M. Handke, W. Mozgawa and M. Rokita, Michrochim. Acta [Suppl] 14 (1997) 511). Differences and similarities have been shown for the spectroscopic data and thus for structures of AlPO₄ and SiO₂.     

Interfacially formed poly(N,N-dimethylaminoethyl methacrylate)/polysulfone composite membranes for CO2/N2 separation

Interfacially formed poly(N,N-dimethylaminoethyl methacrylate)/polysulfone (PDMAEMA/PSF) composite membranes were developed for CO₂/N₂ separation. A layer of PDMAEMA was deposited on a microporous PSF substrate by the solution coating technique, followed by crosslinking with p-xylylene dichloride (XDC) at the interface between the PDMAEMA solid layer and the crosslinking solution. The hydrophilicity and surface free energy of the membranes were analyzed by contact angle measurements with different probe liquids. The permselectivity of the membrane was shown to be affected by the PDMAEMA deposition time, interfacial crosslinking reaction time, and the PDMAEMA and XDC concentrations in the polymer coating solution and the crosslinking solution, respectively. The composite membrane showed a CO₂ permeance of 85 GPU and a CO₂/N₂ ideal separation factor of 50 at 23 °C and 0.41 MPa of CO₂ feed pressure.     

Dissociative excitation of SiH4, SiD4, Si2H6 and GeH4 by 0–100 eV electron impact

We have measured emission cross sections of various electronically excited fragments produced by electron-impact dissociation of SiH₄, SiD₄, Si₂H₆ and GeH₄. At low impact energy (10–20 eV), the measured appearance potentials are correlated to specific dissociation processes. Below 22 eV superexcited states of SiH₄ play a dominant role in the formation of neutral excited fragments. In agreement with the results obtained on alkanes, the cross sections for fragment emission from Si₂H₆ are lower than those for SiH₄. On the other hand, the comparison of cross sections at 100 eV for fragment emission, dissociation and ionization on going from CH₄ to SiH₄ and GeH₄ shows an increase of the probability for production of neutral ground-state fragments at the cost of excited or ionic fragments. Both effects can be explained by a growing probability for internal conversion among the decay channels of superexcited states with increasing number of atoms or electrons in the parent molecule. For each molecule, the H Balmer-emission cross sections at 100 eV are proportional to n^−b, where n 3 is the principal quantum number of the upper state of H and 3 < b < 5 is a parameter characteristic of the parent molecule. Finally, a detailed analysis of the isotopic effect between SiH₄ and SiD₄ on both fragment emission and ionization cross sections from 0 to 100 eV gives strong evidence of the competition between dissociation and autoionization in the decay of superexcited states.     

Thermodynamic properties of the system NH4NO3 + (NH4)2SO4 + H2O at 298.15 K

In this investigation, the mixed aqueous electrolyte system of nitrate and sulfate with common ammonium cation has been studied with the hygrometric method at the temperature 298.15 K. The water activities of the system [yNH₄NO₃ + (1 − y)(NH₄)₂SO₄](aq) are measured at total molalities from 0.4 mol kg⁻¹ up to saturation for different ionic-strength fractions y of NH₄NO₃ with y = 0.2, 0.5 and 0.8. The obtained data allow the deduction of osmotic coefficients. The experimental results are compared with the predictions of the Zdanovskii–Stokes–Robinson (ZSR), Leitzke and Stoughton (LSII), Kusik and Meissner (KM), and Pitzer models. From these measurements, new Pitzer mixing ionic parameters are determined and used to predict the solute activity coefficients in the mixture. The obtained results are used to calculate the excess Gibbs energy at total molalities for different ionic-strength fractions y.     

MFI型分子膜的制备与H2S/CH4分离性能

采用二次生长法在多孔α-Al₂O₃载体上制备MFI型（ZSM-5和silicate-1）分子筛膜;通过XRD和SEM检测,证明所合成的分子筛膜为致密、交联和无取向的MFI型分子筛膜,厚度为5 μm;单组分气体渗透实验检测中,所制备样品膜的N₂渗透量均小于10^-11 mol/（m²·s·Pa）,可认为其无缺陷;同时,考察了样品分子筛膜对H₂S/CH₄混合气的分离效果,在渗透压分别为0.3和0.5 MPa时,silicate-1分子筛膜的H₂S/CH₄的分离因子分别为1.99和4.44,而ZSM-5分子筛膜的CH₄/H₂S的分离因子分别为6.71和12.85。     

Effect of carbon nanotubes addition on electrochemical performance and thermal stability of Li4Ti5O12 anode in commercial LiMn2O4/Li4Ti5O12 full-cell

Li₄Ti₅O₁₂ (LTO)/carbon nanotubes (CNTs) composite material is synthesized based on a solid-state method by sand-milling, spray-drying and calcining at 850 ℃ under N₂ flow. The LTO/CNTs samples with 1 wt% and 3 wt% weight ratio of CNTs addition and the pristine LTO sample are prepared. The rate performance and the thermal stability of these samples are investigated based on LiMn₂O₄ (LMO)/LTO full-cell. The results show that theweight ratio of CNTs addition has distinct effect on LTO performances. The composite materials of LTO composited CNTs have better performance at high-rate due to the intercalation enhancement by conductive network of CNTs. At second, the overcharging temperature response of the cell's surface with 1 wt% CNTs addition is the lowest. The particle size distribution is measured and the most uniform particles are obtained with 1 wt% CNTs addition. This trend could explain that the mediumquantity of CNTs is optimal to improve the heat and mass transfer and prevent the problems of crystallite growing interference and aggregation during the calcination process.     

Thermal studies on the electrical conductivity of some (CnH2n+1NH3)2CuCl4 (n = 1,2) and (CH2)(CH3)2CuCl4 complexes

The electrical conductivities of the compounds (CH₃NH₃)₂CuCl₄, (C₂H₅NH₃)₂CuCl₄ and (CH₂)₂(NH₃)₂CuCl₄ were measured in the temperature range which includes their structural phase transition. The values of the activation energies as calculated from the Arrhenius equation are reported. Confirmation of the phase transition temperatures is carried out using differential thermal analysis in the same temperature range as the conductivity measurements.     

Measurement of C2F4Cl2, CCl4, CHF3 and O2 by wavelength modulation laser atomic absorption spectroscopy of excited Cl, F and O in a dc discharge applying semiconductor diode lasers

The concentrations of C₂F₄Cl₂ and CCl₄, CHF₃ and C₂F₄Cl₂, and O₂ have been measured in a dc gas discharge by wavelength modulation laser absorption spectroscopy of excited chlorine, fluorine and oxygen, respectively, applying semiconductor diode lasers. Argon and helium at reduced pressure were used as plasma gases. Preliminary 3σ detection limits of 0.6–1.5 ppb for chlorine compounds by absorption of the Cl 837.60 nm line, about 70 ppb of fluorine compounds by the F 739.87 nm line, and about 20 ppb oxygen molecules by the O 777.18 nm line were found.     

Co_(3)O_(4)/CeO_(2)复合电极材料的制备与超级电容器电化学性能研究

利用六水合硝酸铈、六水合硝酸钴和尿素通过水热法合成麦叶状Co_(3)O_(4)/CeO_(2)复合电极材料,对其进行电化学性能分析,发现Co_(3)O_(4)/CeO_(2)复合电极材料具有良好的电化学可逆性和功率特性,且其电容特性和大电流放电特性也很优越,是理想的超级电容器材料.     

Thermal studies of novel molecular perovskite energetic material (C6H14N2)[NH4(ClO4)3]

(C6H(14)N2)[NH4(ClO4)3] is a newly developed porous hybrid inorganic-organic framework material with easy access and excellent detonation performances,however,its thermal properties is still unclear and severely hampered further applications.In this study,thermal behaviors and non-isothermal decomposition reaction kinetics of(C6H(14)N2)[NH4(ClO4)3] were investigated systematically by the combination of differential scanning calorimetry(DSC) and simultaneous thermal analysis methods.In-situ FTIR spectroscopy technology was applied for investigation of the structure changes of(C6H(14)N2) NH4(ClO4)3]and some selected referents for better understanding of interactions between different components during the heating process.Experiment results indicated that the novel molecular perovskite structure renders(C6H(14)N2)[NH4(ClO4)3] better thermal stability than most of currently used energetic materials.Underhigh temperature s,the stability of the cage skeleton constructed by NH4^+and ClO4^-ions determined the decomposition process rather than organic moiety confined in the skeleton.The simple synthetic method,good detonation performances and excellent thermal properties make(C6H(14)N2)[NH4(ClO4)3] an ideal candidate for the preparation of advanced explosives and propellants.     

Noncentrosymmetric K2Mn3(SO4)3F2·4H2O and Rb2Mn3(SO4)3F2·2H2O with pseudo-KTP structures

Two fluoride sulfates,K₂Mn₃(SO₄)₃F₂·4H₂O(Ⅰ) and Rb₂Mn₃(SO₄)₃F₂·2H₂O (Ⅱ) are obtained by water solution method.Single-crystal X-ray diffraction analysis indicated that they crystallize in space groups of Cmc2_1.Their structures feature a pseudo-KTP structure consisting of interconnecting[Mn₃(SO₄)3F₂(H₂O)2]_∞ layers,which are further packing along the a axis with alkali metal cations balancing the charges.The structure relationships between the two compounds are discussed.Secondharmonic generation measurements manifest that Ⅰ and Ⅱ have similar second-harmonic generation responses of about 0.2 and 0.25 times that of KH₂PO₄.     

Electrochemical studies on Mo2Cl4(PR3)4 compounds containing phosphines of varied basicity

The electrochemical behaviour of a series of Mo₂Cl₄(PR₃)₄ complexes (PR₃ = PMe₃, PEt₃, PPrⁿ₃,PBuⁿ₃, PH₂Ph, PMe₂Ph, PEt₂Ph, PHPh₂, PMePh₂, PEtPh₂, P(OMe)₃, P(OMe)Ph₂) has been examined by cyclic voltammetry in dichloromethane solution. The phosphines were chosen to provide a wide range of Lewis basicity/π acidity as reflected by Tolman's _co IR and Bodner's Δδ_co ¹³C NMR spectral parameters for Ni(CO)₃(PR₃). The Mo₂ compounds undergo either quasi-reversible or irreversible one-electron oxidations except for P(OMe)₃ and P(OMe)Ph₂ for which no clectroactivity was observed before the solvent limit. The anodic peak potentials, E_p,a, span a range of nearly 700 mV. The half-wave potentials, E_1/2,for the quasi-reversible couples and E_p,a for all were plotted against the IR and NMR values and against the δ → δ* transition energies for the Mo₂ species in dichloromethane and in the solid state. For the organometallic spectral parameters excellent linear correlations were obtained while with the electronic spectral data fair correlations resulted. These results indicate that the Mo₂Cl₄(PR₃)₄ complexes become more difficult to oxidize as the electron-withdrawing nature of the PR₃ substituents increases and the δ → δ* band energy decreases.     

A型沸石/活性炭复合材料的制备及甲烷/氮气吸附分离性能

以沥青和煤矸石为原料,经炭化、活化后获得型体活性炭材料(AC),并在此基础上进行水热晶化,研究晶化时间对复合材料中4A沸石的形成、孔结构和甲烷、氮气吸附性能的影响。通过X射线衍射(XRD)、扫描电子显微镜(SEM)、77 K下的氮气吸附-脱附以及273 K下的CO_2吸附等温线对样品进行表征,结果表明水热晶化后,复合材料中的硅铝形成立方结构的4A沸石,出现了0.45~0.6 nm的微孔,微孔孔容增加,并伴有少量的中孔和大孔。复合材料在298 K下的甲烷(CH_4)和氮气(N_2)吸附等温线的结果表明,晶化时间6 h的复合材料AC-2的甲烷吸附量被提高至10.8 m L/g,并保持较高的CH4/N2平衡分离比(3.7)。     

Membrane purification of Cl2 gas: I. Permeabilities as a function of temperature for Cl2, O2, N2, H2 in two types of PDMS membranes

Permeability (P) of Cl₂, O₂, N₂ and H₂ was measured in polydimethylsiloxane (PDMS) composite membranes with two different degrees of cross-linking. The permeability was measured in the low pressure range (1–3 bar absolute) over a fairly large temperature range 35–120°C. The functionalities of the membranes were compared on the basis of permeation rate and ability to separate the gases Cl₂–O₂. These results are part of an extensive survey where perfluorinated and carbon membranes are also included (not reported here). The purpose of the project is to develop an industrial membrane with high permselectivity for either O₂ or Cl₂ (depending on the type of membrane) at temperatures preferably above 70°C. Process conditions are set in an industrial project. The PDMS membranes are good candidates for this separation, having a high permeation rate for Cl₂ and a selectivity of Cl₂/O₂ in the range of 8–25 depending on temperature. Durability of the PDMS membranes in this aggressive environment is found to be very dependent on process conditions and on how the material is polymerized and cured. For documentation of durability, various silicones were tested; these results are to be reported separately.     

Surface modification of γ-alumina membranes by silane coupling for CO2 separation

Top layers of γ-Al₂O₃ composite membranes have been modified by the silane coupling technique using phenyltriethoxysilane for improving the separation factor of CO₂ to N₂. The separation efficiency of the modified membranes was strongly dependent upon the hydroxylation tendency of the support materials and the amount of the special functional group (i.e. phenyl radical) which was coupled onto a top layer. The separation factor through the TiO₂ supported γ-Al₂O₃ membrane was found to be fairly enhanced by silane coupling, but in case of the -Al₂O₃ supported membrane was not. The CO₂/N₂ separation factor through the modified γ-Al₂O₃/TiO₂ composite membrane is 1.7 at 90°C and ΔP = 2 × 10⁵ Pa for the binary mixture containing 50 vol% CO₂. The separation factor is proportional to the CO₂ concentration in the gas mixture, and the modified membrane is stable up to 100°C. The main mechanism of the CO₂ transport through the modified γ-Al₂O₃ layer is known to be a surface diffusion.     

The infrared spectrum of gaseous Sb4O6

The vibrational spectrum of Sb₄O₆ in the gas phase has been measured at 1000 K by high-temperature infrared spectroscopy. The four infrared-active absorption bands were observed at ν₇ = 785.0 cm¹, ν₈ = 176.2 cm⁻¹, ν₉ = 292.4 cm⁻¹ and ν₁₀ = 415.6 cm⁻¹. By combining these results with data on the molecular geometry and the infrared-inactive modes, as reported in the literature, the thermodynamic functions of Sb₄O₆ have been calculated.     

Tert-butylbenzamidate diruthenium(II, III) compounds. Crystal structure of [Ru2(μ-HNOCC6H4-p-CMe3)4(OPPh3)2]BF4

The reaction between Ru₂Cl(μ-O₂CCH₃)₄ and molten p-tert-butylbenzamide led to the formation of Ru₂Cl(μ-HNOCC₆H₄-p-CMe₃)₄. The polymeric structure of this insoluble compound was broken with AgBF₄, in anhydrous thf, giving [Ru₂(μ-HNOCC₆ H₄-p-CMe₃)₄(thf)₂]BF₄. The reaction of this cationic complex with OPPh₃ gave [Ru₂(μ-HNOCC₆H₄-p-CMe₃)₄(OPPh₃)₂]BF₄. The compounds have been characterized by elemental analysis, spectroscopic data and magnetic measurements and the crystal structure of [Ru₂(μ-HNOCC₆H₄-p-CMe₃)₄(OPPh₃)₂]BF₄ was determined by X-ray crystallography. The asymmetric unit is composed of halves of two different crystallographically independent centrosymmetric cations. Each ruthenium(II,III) dimer is bonded to four bridging p-tert-butylbenzamidate ligands and to two axial triphenylphosphine oxide molecules. The Ru---Ru distances in the two dimeric cations of the unit cell are 2.281(2) and 2.280(2) Å. The compound has a non-polar 2 : 2 arrangement of the tert-butylbenzamidate ligands.     

Magnetic investigation of Cu(NH3)4(NO3)2

The magnetic properties of Cu(NH₃)₄(NO₃)₂ have been measured at low temperatures. Broad maxima in both the susceptibility and specific heat are observed and are consistent with linear chain behavior of a Heisenberg antiferromagnet, with J/k = 3.9 ± 0.1 K. Long-range order sets in at T_c = 0.15 ± 0.01 K, and the ratio kT_c/|J| = 0.038 is the lowest observed as yet for a one-dimensional, S = 1/2 antiferromagnet.     

Preparation of crack-free ZrO2 membrane on Al2O3 support with ZrO2–Al2O3 composite intermediate layers

To develop porous alumina supported MF ZrO₂ membranes, ZrO₂–Al₂O₃ composite intermediate layers are considered in order to decrease stress creation during the processing and avoid cracks formation. The relation between distortion stress and sintering shrinkage was experimentally studied. And the cracks formation mechanism was qualitatively evaluated and discussed. Finally, crack-free YSZ membrane with pore size of 0.16 μm on the two ZrO₂–Al₂O₃ intermediate layers possessing a gradient composition was successfully prepared and characterized.