拉伸和加热对磺化聚苯醚/凝胶薄膜导电性能的影响

在静态热力学分析仪上选择不同的拉力与受热条件拉伸磺化聚苯醚/凝胶薄膜,研究拉伸和加热对复合膜导电性能的影响.研究发现该复合薄膜的质子电导率随着拉伸率的增加而增大,SEM表明复合薄膜在拉伸后形成了更多、更长的离子传递通道,促进了水合质子的传递.SEM和热重分析也表明该磺化聚苯醚/凝胶薄膜能吸附更多的水分子,使得电导率增大.     

Synthesis,characterization and application of biopolymer-ionic liquid composite membranes

Biopolymer composite membranes based on chitosan doped with an ionic liquid (IL) 1-ethyl 3-methylimidazolium thiocyanate (EMImSCN) have been developed and characterized. The doped ionic liquid films show remarkable enhancement in ionic conductivity (σ). The Fourier transform infrared (FTIR) spectroscopy, atomic force microscopy (AFM) and X-ray diffraction studies (XRD) affirmed the composite nature, good incorporation of ionic liquid and reduction in crystallinity of films, respectively. The interaction between ionic liquid, chitosan and iodide polymer electrolyte matrix was evaluated by cyclic voltammetry. The fabricated dye sensitized solar cell (DSSC) using this new biopolymer electrolyte membranes shows promising performance.     

Properties of modified Nafion® membranes with heavy amount of (3-mercaptopropyl) trimethoxysilane prepared by long-term infiltration

Modified Nafion® membranes with a large amount of (3-mercaptopropyl) trimethoxysilane (MPTS) were fabricated by a long-term infiltration process. MPTS has been known as a strong surface modifier due to its ability to form inorganic phases having a high concentration of sulfonic acid ligands by proper oxidation of thiol-groups. In this work, the long-term infiltration of 3-mercaptopropyltrimethoxysilane (MPTS) monomers into the Nafion® matrix was performed to achieve the goal of reducing methanol crossover without sacrificing proton conductivity. Thiol (-SH) groups of MPTS molecules were converted into sulfonic acid groups by mild oxidation with hydrogen peroxide (H₂O₂). The fabricated membranes were characterized through microstructure observation, solvent uptake and expansion test, and proton conductivity measurement. The MPTS-derived inorganic phase formed in the ionic cluster pathways and the free volume in the Nafion® matrix could significantly reduce the methanol transfer rate, keeping high proton conductivity due to an increase in sulfonic acid concentration induced from the oxidation of the infiltrated MPTS.     

Synthesis & Characterization of PVA/STA Composite Polymer Electrolyte Membranes for Fuel Cell Application

Chemically cross-linked composite membranes consisting of poly(vinyl alcohol) (PVA) and silicotungstic acid (STA) have been prepared by solution casting and evaluated as proton-conducting polymer electrolytes. The proton conductivity of the membranes was investigated as a function of blending composition, cross-linking density, and temperature. The conductivity mechanism was investigated by using Impedance spectroscopy in the region between 40 Hz and 10 MHz. Membranes were also characterized by FTIR spectroscopy to confirm the crossl-inking reaction and differential scanning calorimetry (DSC) to assess the thermal stability. Membrane swelling decreased with increase in cross-linking density accompanied by improvement in mechanical properties. The proton conductivity of the membranes was of the order of 10⁻³ S/cm and showed similar resistance to methanol permeability as Nafion 117 under the same measurement conditions.     

Poly(propargyl alcohol) doped with sulfuric acid,a new proton conductor usable for humidity sensor construction

The electrical properties of poly(propargyl alcohol), chemically doped with sulfuric acid, were investigated as a function of the relative humidity. In the absence of water, the conductivity of the doped polymer is very low (about 3 × 10⁻⁹ S cm⁻¹ at 25 °C) with characteristics of electronic-type charge transfer. In the presence of humidity, the charge transfer inside the polymer is mainly due to proton motion and the conductivity, ionic in character, increases with exponential trend as a function of the relative humidity. An explanation of this behaviour is attempted by taking into account the effect of water on the ion interaction. A preliminary investigation on the possibility of the use of the acid-doped poly(propargyl alcohol) as humidity sensor was also carried out.     

Proton conductivity in perovskite type yttrium doped barium hafnate

Yttria doped Ba-hafnates were prepared by solid state route and the proton conductivity of pressed samples of yttria doped barium hafnate was determined with impedance spectroscopy. The results are compared with existing data for cerates and zirconates. It was found that Ba-hafnates show a level of proton conduction that is comparable to that of doped Ba-zirconates at low and slightly higher at high temperatures. This is in agreement with the prediction based on the ionic radius of the tetravalent atom in the perovskite.     

凝胶掺杂磺化聚苯醚膜性能及水分子的动态吸附

将H3PO4/SiO2凝胶掺杂入磺化聚苯醚质子交换膜基质中,提高了吸水率和质子电导率。研究了水分子在凝胶掺杂型磺化聚苯醚膜中的动态吸附扩散行为,探讨了水与膜基质中磺酸和磷酸基团的相互作用及变化,研究了凝胶掺杂型磺化聚苯醚膜的质子传导过程。结果表明,复合膜的水吸附量显著增加,电导率提高,最高可超过Nafion112(0.0871S·cm-1),达到0.216S·cm-1。凝胶对提高复合膜的电导率具有重要作用,一方面,磷酸基团在磺酸基团和水分子作用下离解产生了离域的H+,增加了可移动的离子数总量;另一方面,凝胶由于强烈的亲水性可吸附水分子形成新的亲水区,并在水合离子的跃迁和传导过程中起着连接点的作用,从而形成更多更长的水分子区,促进了传导质子的离子簇和离子通道的形成,显著提高了电导率。     

Alkali doped poly(vinyl alcohol) for potential fuel cell applications

Optical transparent, chemically stable alkaline solid polymer electrolyte membranes were prepared by incorporation KOH in poly(vinyl alcohol) (PVA). The distributions of oxygen and potassium in the membrane were characterized by XRD and SEM–EDX. It is demonstrated that combined KOH molecules may exist in the PVA matrix, which allow it to be an ionic conductor. In particular, the chemical and thermal stabilities were investigated by measuring changes of ionic conductivities after conditioned the membrane in various alkaline concentrations at elevated temperatures for 24 h for potential use in fuel cells. The membranes were found very stable even in 10 M KOH solution up to 80 °C without losing any membrane integrity and ionic conductivity due to high dense chemical cross-linking in PVA structure. The measured ionic conductivity of the membrane by AC impedance technique ranged from 2.75 × 10^?4 S cm^?1 to 4.73 × 10^?4 S cm^?1 at room temperature, which was greatly increased to 9.77 × 10^?4 S cm^?1 after high temperature conditioning at 80 °C. Although, a relatively higher water uptake, the methanol uptake of this membrane was one-half of Nafon 115 at room temperature and 6 times lower than that of Nafion 115 after conditioned at 80 °C. The membrane electrolyte assembly (MEA) fabricated with PVA–KOH in direct methanol fuel cell (DMFC) mode showed an initial power density of 6.04 mW cm^?2 at 60 °C and increased to 10.21 mW cm^?2 at 90 °C.     

Development and characterization of ionic liquid doped solid polymer electrolyte membranes for better efficiency

Solid polymer electrolyte membranes based on poly(ethylene oxide) (PEO) polymer electrolyte incorporated with low viscosity ionic liquid (IL), 1-ethyl 3-methylimidazolium trifluoromethanesulfonate (EMImTFO^?) have been prepared and used in dye-sensitized solar cell (DSSC) application. Ionic conductivity (σ) measurement shows improvement in σ due to reduced crystallinity and free charge carriers provided by IL which was further affirmed by our differential scanning calorimetry (DSC) and optical microscopy (OM) measurements. Surface feature of films was characterized by scanning electron microscopy (SEM) measurement. The photovoltaic characteristics of the fabricated DSSC are compared with those without IL, in which the low viscosity IL doped solid polymer electrolyte system shows excellent improvement in efficiency.     

Preparation and characterization of SMA/S-POSS hybrid membranes for direct methanol fuel cell applications

A novel sulfonated polyhedral oligomeric silsesquioxane(S-POSS) monomer was synthesized successfully in this article. S-POSS acted as a donor of sulfonic acid group and reacted with poly(styrene-co-maleic anhydride) (SMA). FT-IR spectroscopy confirmed the modification through introduction of peaks characteristic of ester linkages and carboxylic groups. The SMA/S-POSS hybrid membranes were fabricated from different S-POSS contents. The proton conductivity and methanol permeability of the hybrid membranes were studied with changing S-POSS content from 5wt.% to 30wt.%. It was found that the proton conductivity and the methanol permeability were dependent on the S-POSS content. Both of proton conductivity and methanol permeability properties improve with increasing S-POSS content. The proton conductivities of the hybrid membranes are in the range of 10-3-10-2 S·cm-1,and the range of methanol permeabilities was between 10-8 and 10-7 cm2·s-1. The membranes show good thermal properties characterized by thermogravimetric analysis (TGA).     

Eu掺杂对LiNiPO_4导电性的影响(英文)

采用Pechini方法制备了掺杂Eu和未掺杂Eu的LiNiPO4化合物,通过热重分析和差热分析(TG/DTA)来确定LiNiPO4的生成温度。粉末X射线衍射谱证实所得到的化合物为具有正交结构的纯LiNiPO4。采用复合阻抗谱技术分析样品在不同的温度和频率下的电导率和模量谱。采用Almond和West公式计算导电性能参数,如离子跃迁频率、电荷载体浓度。掺杂1.0%Eu的LiNiPO4的离子电导率增加了一个数量级。电模量谱分析表明LiNiPO4化合物中存在非德拜类型的弛豫。     

The oxidation behavior of a Zr-0.5Y alloy

A Zr-0.5 Y alloy was found to oxidize about 6 times faster than pure zirconium over the temperature range of 400 to 565°C. The activation energies were nearly identical (32 kcal/mole). The activation energies correspond to grain boundary diffusion of oxygen through the scale. The higher oxidation rate of the alloy was attributed to a higher anion vacancy concentration and the assumption that diffusion sites in the lattice and boundaries were in local equilibrium. Measurements on yttria-doped zirconia showed that ionic conductivity was increased markedly by yttrium and extended over a wide range of oxygen pressure. The defect structure of the doped oxide was changed to one of oxygen vacancies, even at the high end of the oxygen pressure range, 10^–8 to 0.2 atm, over which pure ziconia contains oxygen interstitials. The doped oxide was found to be extrinsic over the entire range of oxygen pressure and, although ionic conductivity predominated, electronic conductivity was still appreciable. The electronic conductivity, however, was still sufficiently high so that electron transport was not rate-controlling in the predominantly ionic-conducting scale.     

PTFE coated Nafion proton conducting membranes for direct methanol fuel cells

The performances of direct methanol fuel cells (DMFC) are affected by the methanol cross-over, due to the concentration gradient and electrosmosis between the anodes and cathodes. In this study, Polytetrafluoroethylene (PTFE) has been sputter deposited on conventional proton conducting membranes, Nafion117. It was found that the problem of the methanol cross-over was eased by the PTFE coating. The properties of coated and uncoated Nafion117 were investigated by scanning electron microscopy, electron spectroscopy for chemical analysis, gas chromatography and AC impedance spectroscopy. The coated film can form a barrier layer between the methanol solution and the polymer membrane. The PTFE barrier layer can effectively retard the methanol molecules, whereas the proton conductivities were not significantly influenced. The conductivity/permeability ratio two times higher the conventional Nafion117 membrane has been achieved under an optimized coating time. This technique developed shows great potential for the applications in DMFCs.     

Properties of low-modulus sodium silicate solution in alkali system

The properties of low-modulus (m≤1) sodium silicate and pre-desilication solutions in alkali systems were studied by measuring their electrical conductivity, viscosity, and surface tension. The results show that the property of high concentration pre-desilication solution is similar to that of sodium silicate solution. The electrical conductivity of sodium silicate solution increases with increasing the temperature and silica concentration but decreases with increasing the modulus. Further, the viscosity of the solution increases with increasing the silica concentration and linearly decreases with increasingthe temperature, whereas its surface tension gradually decreases with increasingsilica concentration and temperature, indicating that the sodium silicate solution is an oligomer with strong surface activity. At room temperature, the electrical conductivity and surface tension of sodium silicate solution are higher than those of pre-desilication solution, whereas its viscosity is smaller than that of pre-desilication solution. A turning point exists at a silica concentration of 44.7 g/L. When the silica concentration is less than 44.7 g/L, the ionic structure of the solution is dominated by monomeric silicate ions. In contrast, when the silica concentration changes from 44.7 to 50 g/L, the migration number of silicate anions significantly decreases.     

13C CPMAS NMR,XRD, d.c. and a.c. electrical conductivity of aromatic acids doped polyaniline

Aromatic acids, para-toluene sulfonic acid (PTSA) and sulfosalicylic acid (SSA), doped polyanilines at different dopant levels and prepared by chemical and electrochemical methods are characterized by the high-resolution solid-state ¹³C CPMAS NMR technique. X-ray diffraction (XRD) patterns of highly protonated samples show a peak around 24 °. There is increase in crystallinity as the dopant concentration is increased. Temperature dependence of d.c. electrical conductivity measurements suggests that conduction takes place in an inhomogeneous medium consisting of ‘metallic’ polymer particles embedded in an insulating matrix. A.c. electrical conductivity measured on some of these samples shows that σ_ac ∝ ω^s in the frequency range 10 Hz to 100 kHz, and s is found to decrease as the dopant concentration and the temperature are increased. For higher dopant concentration samples, σ_ac is found to be temperature independent in the frequency range 10 Hz–100 kHz. The real part of the dielectric constant showed a steep increase at low frequencies. The results of a.c. transport are discussed in terms of hopping of charges among defect states.     

Structural changes during annealing and during acceptor doping of oriented poly(p-phenylene sulfide)

Thermally-annealed, melt-formed poly(p-phenylene sulfide), PPS, has a folded-chain, lamellar structure with a repeat period varying from 90 Å to 160 Å, depending upon the annealing temperature. Local crystalline order develops in the polymer before the onset of extensive lamellar ordering. On doping oriented PPS with AsF₅, the polymer swells and loses both crystallinity and chain orientation. The absence of crystalline and lamellar reflections in doped PPS probably results from dopant-induced structural disorder and chemical reactions (formation of dibenzothiophene linkages and crosslinking). These structural changes may explain the relative insensitivity of the conductivity of the doped polymer to the degree of crystallinity and orientation in the precursor polymer.     

The role of ionic conductivity and interface in electrical resistance,ion transport and transmembrane redox reactions through polyaniline membranes

Three different physico-chemical properties of HCl-doped polyaniline (PANI) membranes, separating two aqueous solutions are compared. The first one is electrical conductivity measured with electrochemical impedance spectroscopy (EIS). The second one is H⁺ ion permeation through the membrane under pH gradient, measured with pH electrodes, and the third is electron/ion coupled counter transport in a transmembrane redox reaction, measured with redox electrodes. Electrophysical properties of undoped membrane are not described by the Ohm's law. The non-linear dependence is due to a limited content of mobile electrons and is similar to the Child's law known for vacuum diodes and dielectrics. Although the impedance of the doped membrane separating aqueous solutions is much less than that for the undoped membrane, it is determined by ions and not by electrons. For doped membranes the ratio of ion diffusion coefficient and charge drift mobility, determined in the external electrical field, is close to the Einstein relationship, meaning that the same ions play the key role in both processes. Thickness dependent behaviour is used to differentiate the interfacial properties from those of the bulk properties of the membrane. Interpolation of properties to zero membrane thickness shows that the interfacial charge transport plays an important role in doped membrane impedance and influences ion and redox transport rates. The relative role of interface versus volume increases with acid doping, which makes the bulk membrane volume more permeable for ions.     

Constitutional Design and Dielectric Properties of BST Graded Ceramics

The effect of B203 dopant and SrTiO3 (ST) content on lattice parameters and ferro-paraelectric phase transition temperature (i.e. Curie point) of Ba1-xSrxTiO3 (BST, x=0～0.4) ceramics was investigated, and then BST graded ceramics with controllable transition temperature zone were fabricated and characterized for their dielectric properties. The results show that with the increase of ST content, c/a ratio and Curie point of both doped and undoped ceramics decreased linearly but with different rate of change, resulting from different ionic radiuses of Ba^2 , Sr^2 and B^3 . Moreover, both c/a ratio and Curie point of doped BST increased slightly in comparison with that of undoped ones while the Curie point changed scarcely with dopant amount rising, which perhaps means that for BST grains with different ST content, B2O3 solubility was different but limited and most of boron (B) did not incorporate into BST grains. Through controlling composition,transition temperature of graded ceramics can be designed. For doped graded ceramics sintered at 1250℃, its dielectric properties was much better than that of undoped one sintered at 1400℃, and Curie peak of both samples was broadened effectively via graded structure.     

直接甲醇燃料电池关键材料的表面改性及其研究进展

直接甲醇燃料电池(DMFC)由于结构简单、能量密度大、无污染等优点,已经成为近年来国内外研究的热点之一。简要介绍了直接甲醇燃料电池的原理,重点概述了阳极催化剂和电解质膜这两个决定电池性能的关键材料的表面改性及其研究进展。介绍了提高直接甲醇燃料电池阳极催化剂催化活性的各种改性技术,如通过离子溅射法、分子束法等传统物理方法对电极表面进行修饰,在电极材料中掺杂对甲醇催化活性较好的纳米材料等。此外,还介绍了基于降低甲醇渗透率的Nafion膜改进技术,如通过等离子蚀刻法等物理手段对膜表面进行改性,掺杂阻醇性能较好的无机化合物等。并介绍了几种具有应用前景的新型替代膜,如接枝膜、共混膜等。最后对直接甲醇燃料电池的发展应用进行了展望。     

CaO掺杂10NiO-NiFe2O4复合陶瓷的导电性能

研究添加剂CaO含量和烧结温度对CaO掺杂10NiO-NiFe2O4复合陶瓷的物相组成和电导率的影响。结果表明:CaO含量在0~4%范围内,烧结试样的X射线衍射谱仅有NiO和NiFe2O4的衍射峰;10NiO-NiFe2O4复合陶瓷在空气中升温过程存在明显的吸氧和失氧行为;CaO含量对1 473 K烧结的10NiO-NiFe2O4复合陶瓷的电导率影响显著;当CaO含量为0~1%时,随测试温度的升高,材料电导率逐渐增大,随后在773~923 K出现1~2个数量级的突降,然后重新缓慢增大;当CaO含量为2%和4%(质量分数,下同)时,材料电导率在298~1 233 K范围内随着测试温度的升高而增大;2?O掺杂10NiO-NiFe2O4复合陶瓷在不同测试温度下均具备最高电导率,1 233 K下达到16.29 S/cm,远高于未掺杂试样的1.03 S/cm;烧结温度由1 473 K提高到1 573 K时,未掺杂试样在1 233 K时电导率提高近15倍,2?O掺杂试样1 233 K时电导率略有提高。