Calorimetric characterization of membrane materials based on polyvinyl alcohol

There is ample scope for modification of polyvinyl alcohol (PVA) to derive diverse range of properties because of the presence of hydroxyl group in its chain. In the present work, PVA has been modified to carboxymethylated polyvinyl alcohol (CPVA) — a carboxy-functionalized membrane material. Generally the cohesive energy density has incremental influence on the melting point and mechanical strength of a material but in this case of CPVA even though theoretical cohesive energy density of CPVA is lower than that of PVA but paradoxically its mechanical strength was found to be higher than that of PVA (∼202 vis-à-vis 207°C and ∼174 vis-à-vis ∼58 MPa, respectively). Calorimetric evaluation along with the energy balance concept have provided meaningful information to justify such paradoxical feature as a result of the dominating role of intermolecular hydrogen bonding in CPVA to compensate for its relatively lower cohesive energy density typically 0.05 J m^−3/2. Thermal analysis has been made to examine the role of PVA and its carboxymethylated derivative (CPVA) towards moisture. It was observed that PVA membrane surface became sticky on exposure to water at 30°C for a period of 30 min, whereas under the same condition CPVA counterpart remained practically unaffected.     

Nanoscale membrane electrode assemblies based on porous anodic alumina for hydrogen–oxygen fuel cell

In this paper, we demonstrate that nanoscale membrane electrode assemblies, functioning in a H₂/O₂ fuel cell, can be fabricated by impregnation of anodic alumina porous membranes with Nafion® and phosphotungstic acid. Porous anodic alumina is potentially a promising material for thin-film micro power sources because of its ability to be manipulated in micro-machining operations. Alumina membranes (Whatman, 50 μm thick, and pore diameters of 200 nm) impregnated with the proton conductor were characterized by means of scanning electron microscopy, X-ray diffraction, and thermal analysis. The electrochemical characterization of the membrane electrode assemblies was carried out by recording the polarization curves of a hydrogen–oxygen 5 cm² fuel cell working at low temperatures (25?÷?80 °C) in humid atmosphere. Our assemblies realized with alumina membranes filled with phosphotungstic acid and Nafion® reach respectively the peak powers of 20 and 4 mW/cm² at room temperature using hydrogen and oxygen as fuel and oxidizer.     

Research on the electrochemistry of oxygen ion conductors in the former Soviet Union. I. ZrO2-based ceramic materials

Developments of solid electrolytes and mixed conductors based on stabilized zirconia in the former Soviet Union are reviewed. Primary attention is given to experimental data on high-conducting electrolytes, mixed conductors obtained by doping zirconia with transition metal oxides, oxygen exchange and oxygen permeation processes, as well as properties of metal electrodes in contact with the stabilized zirconia. Received: 26 March 1998 / Accepted: 4 June 1998     

Comparative effect of phthalazinone units in sulfonated poly(arylene ether ether ketone ketone) copolymers as proton exchange membrane materials

A new series of aromatic poly(arylene ether ether ketone ketone) copolymers containing pendant sulfonic acid groups (SPAEEKK‐D) were synthesized from commercially available monomers 1,3‐bis(4‐fluorobenzoyl)‐benzene, sodium 6,7‐dihydroxy‐2‐naphthalenesulfonate, and 4‐(4‐hydroxyphenyl)‐2,3‐phthalazin‐1‐one (DHPZ). Structure–property relationships of the phthalazinone SPAEEKK‐D series poly(arylene ether ether ketone ketone) copolymer were compared with copolymers SPAEEKK‐B and SPAEEKK‐H containing different diols such as 4,4′‐biphenol and hydroquinone, respectively, prepared in our earlier work. Ion exchange capacity (IEC_w, weight‐based; IEC_v, volume‐based), thermal stabilities, swelling, proton and methanol transport properties of the membranes were investigated in relation to their structures and compared with those of perfluorinated ionomer (Nafion 117). The SPAEEKK‐D membrane incorporating the phthalazinone monomer DHPZ showed relatively lower water uptake and methanol permeability compared with earlier SPAEEKK‐B and SPAEEKK‐H membranes incorporating biphenol and hydroquinone monomers, respectively. Inclusion of phthalazinone in the SPAEEKK‐D copolymers led to lower water absorption, enabling increased proton exchange concentrations in the hydrated polymer matrix that resulted in more desirable membrane properties for future direct methanol fuel cell applications. The SPAEEKK‐D membranes also showed improved mechanical and thermal properties and oxidative stability compared with the earlier SPAEEKK‐B and ‐H membranes. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 989–1002, 2008     

基于质子交换膜燃料电池的热电联产系统的研究进展

基于质子交换膜燃料电池的热电联产系统利用电池发电时产生的余热供热,提高了能源利用率,实现了热电供能的可持续发展。本文介绍了基于质子交换膜燃料电池的热电联产系统工作原理,概述了各子系统的组成及功能,重点围绕建模方法、操作模式、运行策略、评价方法及系统优化等方向综述了当前研究的进展情况,指明了后续研究可从多尺度综合性建模、完善配置细节及增加集成选项、预测能源需求及运行智能化、多维度系统评价以及节能降耗等方面进行。     

通过氢键构筑的混合配体3D超分子及电化学性质

在水热条件下合成了配位聚合物[Co(H2O)6].[Co(phen)2(H2O)2]2·(BTC)2·24.6H2O(phen=1,10-邻菲罗林,BTC=均苯三甲酸),并通过元素分析,IR光谱,TGA和单晶X射线衍射对其进行了表征,结构表明该化合物属于单斜晶系,空间点群P2(1)/c.晶体的不对称结构单元中包含1个均...     

Hybrid materials based on vanadium pentoxide intercalation complexes

Neutral macrocyclic compounds (crown ethers and cryptands) and charged molecular species (alkylammonium iodides) were intercalated into vanadium oxide xerogel (V₂O₅ · nH₂O) to study their influence on the electrical behaviour of this inorganic 2D host lattice. Treatment with alkyl or arylammonium iodide solutions produced the intercalation of organic cations accompanied by the reduction of a fraction of V (V) to V (IV). Characterisation by different techniques allowed the postulation of the interlayer arrangement of the guest species. The study of electrical behaviour at different temperatures indicated that the properties of the hybrid materials can be mainly related to the nature of guest species, the degree of host lattice reduction, the interlayer water content, and the␣presence of metal ions deliberately introduced in the system. Received: 23 January 2001 Accepted: 5 April 2001     

Electric and thermogravimetric properties of brownmillerites based on barium oxides

The electric and thermogravimetric properties of oxygen-deficient perovskite-like complex oxides Ba₂HoGaO₅, Ba₂YGaO₅, Ba₂ScInO₅, and Ba₂Sc₂O₅ are studied. It is found that these phases are capable of intercalating water from a gas phase; however, the total water amount is smaller than the supposed nominal concentration of oxygen vacancies calculated from formula A₂BB′O₅[V _O]₁. A comparison of the temperature dependences of conductivities suggests that the highest oxygen-ion conductivity is inherent in the phases with a statistical arrangement of oxygen vacancies (Ba₂Sc₂O₅, Ba₂ScInO₅). In a humid atmosphere (when the contribution of proton conductivity is significant), the total conductivity alters in line with the oxygen-ion conductivity, i.e. it increases in the series Ba₂YGaO₅-Ba₂HoGaO₅-Ba₂ScInO₅-Ba₂Sc₂O₅.     

Organic electrochemical transistors based on PEDOT with different anionic polyelectrolyte dopants

Recent applications of organic electrochemical transistors (OECTs) in bioelectronics motivate the search for new materials with mixed electronic and ionic conductivity. We investigate the characteristics of a series of poly(3,4-ethylenedioxythiophene) (PEDOT)-based materials with a new class of anionic polyelectrolytes used as dopants and stabilizers, replacing the traditionally used poly(styrene sulfonate) (PSS). We show that the backbone of the polyanion plays a major role in determining device performance, while its molecular weight and the counter ion used during PEDOT synthesis play a less important role. We find that transconductance increases with the degree of swelling of the film, consistent with enhanced ion transport. Finally, we identify a polymer that offers performance close to the state-of-the-art. This work highlights the importance of the polyanion phase as a means to control OECT performance. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016, 54, 147–151     

Composite materials based on zeolite 4A for adsorption heat pumps

Some additives and binders were chosen for the preparation of 4A-zeolite-based composites with high equivalent thermal conductivity for heat pumps application. Additives (SiC, Si₃N₄, graphite) and binders (PTFE, Al(OH)₃) were tested for their effectiveness in terms of equivalent thermal conductivity and maximum water adsorption capacity of the composites. The influence of the equivalent thermal conductivity of the composite adsorbents on the specific power of the heat pump was also calculated. Results show a significant improvement in the equivalent thermal conductivity of the composite samples which are prepared using aluminum hydroxide as binder, over that of zeolite pellet beds. Such composite materials could be used to build adsorption heat pumps with higher specific power and, consequently, with lower investment cost.     

A new anhydrous proton conducting material based on phosphoric acid doped polyimide

A new anhydrous proton conducting material based on polyimide and phosphoric acid composite was prepared. The interaction between polyimide (PI) and phosphoric acid was investigated by FTIR. The results show that phosphoric acid interacts with polyimides mainly by hydrogen bonds rather than by protonation of PI at room temperature. Environmental scanning electron microscopy (ESEM) was employed to study the surface morphology of the membranes. The results show that the surface of PI-xH₃PO₄ membranes is very compact and homogeneous. Proton conductivity and methanol permeability of PI doped with phosphoric acid (PI-xH₃PO₄) were also studied. Proton conductivity of PI-xH₃PO₄ membranes increases with increasing concentration of phosphoric acid. Hydrogen bond seems to play an important role in the proton conductivity of this system. Effects of osmotic on the direct diffusion process of methanol in the membranes can be negligible due to the absence of micro-pore structure as already shown in ESEM results. Effects of methanol concentration and temperature on the methanol permeability of PI-xH₃PO₄ membranes were also discussed. Methanol permeability in PI-xH₃PO₄ membranes decreases with increasing methanol concentration, and increases with increasing temperature.     

基于绿色氢科学理念构筑从低碳制氢到高效储氢的氢能体系

本文从低碳制氢和高效储氢的角度思考及探讨氢能体系绿色化发展过程中的关键科学问题.提出＂绿色氢科学＂理念与＂低碳制氢,高效储氢＂技术发展路线图,以期通过相关科学问题的认识,来构建具有高度原子经济性及可持续性的绿色氢能体系.     

不同直链二胺对敏化石墨烯制氢光催化剂性能的影响

采用一步水热法合成方法,分别利用乙二胺(1,2-EDA),1,3-丙二胺(1,3-PDA), 1,4-丁二胺(1,4-BDA)和1,5-二胺基戊烷(1,5-PDA) 4种不同碳链长度的直链二胺与氧化石墨烯(GO)进行胺缩合反应(ACR),在GO表面构筑了链接基团,再利用这些经过化学修饰的GO为载体,构筑了染料敏化的光催化剂,研究了它们在可见光辐照下的产氢性能.结果表明,用乙二胺经ACR反应处理的GO呈现出皱褶结构,所制备的催化剂较未处理催化剂的产氢活性高出1.9倍,反应2 h产生1308.6μmol的氢气,而用其它二胺处理过的GO活性并没有明显变化.多种表征方法的结果表明,乙二胺通过ACR反应在GO上形成了具有共轭特性的皱褶官能团,这些官能团缩短了在GO表面电荷传输路径,提高了催化剂的电荷传导能力,催化剂表现出更高的电导率、更长的激子寿命,制氢催化活性也更高.相反,其它二胺不能形成具有共轭特性的官能团,因此催化活性变化不明显,甚至还有降低.结果表明,在GO上修饰适当的官能团是一种构筑高效太阳能光催化制氢催化剂的新策略.     

Electrochemical properties of composite materials based on platinum modified with molybdenum compounds

The composite coating Pt-MoOx is produced by an electrochemical technique under potentiodynamic conditions on the surface of a preliminarily prepared electrode of glassy carbon. The inclusion of molybdenum into the composition of the obtained electrode deposit is confirmed by the data of cyclic voltammetry and the secondary-electron emission spectra. In the cyclic voltammograms that are obtained in a 2 M solution of sulfuric acid one can distinguish a pair of peaks at potentials equal to 0.46 V (anodic run) and 0.3 V (cathodic run), which are connected with the redox transitions experienced by molybdenum compounds. It is discovered that the obtained deposit possesses catalytic properties with respect to the oxygen reduction reaction. The number of electrons that are corresponding to the redox transitions experienced by molybdenum compounds is calculated. It amounts to 0.27 electrons per molybdenum atom.     

Studies on the preparation of active oxygen-deficient copper ferrite and its application for hydrogen production through thermal chemical water splitting

Hydrogen generation through thermal chemical water splitting technology has recently received in- creasingly international interest in the nuclear hydrogen production field. Besides the main known sulfur-iodine (S-I) cycle developed by the General Atomics Company and the UT3 cycle (iron, calcium, and bromine) developed at the University of Tokyo, the thermal cycle based on metal oxide two-step water splitting methods is also receiving research and development attention worldwide. In this work, copper ferrite was prepared by the co-precipitation method and oxygen-deficient copper ferrite was synthesized through first and second calcination steps for the application of hydrogen production by a two-step water splitting process. The crystal structure, properties, chemical composition and δ were investigated in detail by utilizing X-ray diffraction (XRD), thermogravimetry (TG) and differential thermal analysis (DTA), atomic absorption spectrometer (AAS), ultraviolet spectrophotometry (UV), gas chro- matography (GC), and so on. The experimental two-step thermal chemical cycle reactor for hydrogen generation was designed and developed in this lab. The hydrogen generation process of water splitting through CuFe2O4-δ and the cycle performance of copper ferrite regeneration were firstly studied and discussed.     

A composite proton-conducting membrane based on a poly(vinylidene)fluoride-poly(acrylonitrile), PVdF-PAN blend

This paper reports on the synthesis and the properties of a new microporous, composite proton-conducting gel membrane, formed by swelling a poly(vinylidene)fluoride- poly(acrylonitrile), PVdF-PAN blend-based matrix containing a dispersed Al₂O₃ ceramic filler with aqueous acid solutions. We show that this membrane has a high and stable conductivity, a proton transport not critically influenced by the relative humidity level, and a projected low cost. Tests in a methanol-air laboratory cell also demonstrate that the membrane is basically suitable for application in direct methanol fuel cells.     

Functional organic materials based on polymerized liquid-crystal monomers: supramolecular hydrogen-bonded systems

Functional organic materials are of great interest for a variety of applications. To obtain precise functional properties, well-defined hierarchically ordered supramolecular materials are crucial. The self-assembly of liquid crystals has proven to be an extremely useful tool in the development of well-defined nanostructured materials. We have chosen the illustrative example of photopolymerizable hydrogen-bonding mesogens to show that a wide variety of functional materials can be made from a relatively simple set of building blocks. Upon mixing these compounds with other reactive mesogens, nematic, chiral nematic, and smectic or columnar liquid-crystalline phases can be formed that can be applied as actuators, sensors and responsive reflectors, and nanoporous membranes, respectively.     

Facile deposition of cobalt oxide based electrocatalyst on low-cost and tin-free electrode for water splitting

Facile deposition of a water-splitting catalyst on low-cost electrode materials could be attractive for hydrogen production from water and solar energy conversion. Herein we describe fast electrodeposition of cobalt-based water oxidation catalyst(Co-WOC) on simple graphite electrode for water splitting. The deposition process is quite fast, which reaches a plateau in less than 75 min and the final current density is～1.8 mA/cm2under the applied potential of 1.31 V at pH = 7.0. The scanning electron microscopy(SEM) study shows the formation of nanometer-sized particles(10-100 nm) on the surface of the electrode after only 2 min and micrometer-sized particles(2-5 μm) after 90 min of electrolysis. X-ray photoelectron spectroscopy(XPS) data demonstrate the as-synthesized ex-situ catalyst mainly contains Co2+and Co3+species incorporating a substantial amount of phosphate anions. These experiments suggest that cost-efficient cobalt oxide materials on graphite exhibit alluring ability for water splitting, which might provide a novel method to fabricate low-cost devices for electrochemical energy storage.     

Mobility of small molecules in membrane materials based on copolyimide P84

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