A novel proton-conductive membrane with reduced methanol permeability prepared from bromomethylated poly(2,6-dimethyl-1,4-phenylene oxide) (BPPO)

A series of proton-conducting membranes were developed for direct methanol fuel cell (DMFC) applications via sulfonation of bromomethylated poly(2,6-dimethyl-1,4-phenylene oxide) (BPPO) base membranes. Besides the low manufacture cost, the membranes exhibited an excellent control on methanol crossover and swelling, and a sound balance with high proton conductivities. These can be attributed to the inherent properties of membrane structures: (i) benzyl substitution with bromine, which imparted the membrane stronger hydrophobicity, (ii) cross-linking between BPPO chains, which enhances the dimensional stability and renders the membrane a dense texture, (iii) proper content of sulfonic acid groups, which guarantees the proton conductivity. An optimal membrane was obtained after investigating the effects of the bromination degree and sulfonation process on the performances of corresponding membranes, i.e., the membrane possesses the methanol permeability of 2.64 × 10⁻⁸ cm²/s and characteristic factor Φ value of 30 times higher than that of Nafion^® 117. The sulfonation process should be controlled within a proper period of time and in mild sulfonation conditions so as to achieve a proton conductivity higher than 0.07 S/cm for potential applications in DMFC.     

Nitrogen-rich Graphdiyne Film for Efficiently Suppressing the Methanol Crossover in Direct Methanol Fuel Cells

The inhibition of the methanol crossover is one of the intractable challenges in the direct methanol fuel cell.The graphdiyne(GDY)with atomic-level pores shows great potential in realizing the zero-permeation of methanol molecules.In this paper,an ultrathin layer of nitrogen-rich GDY film with a high nitrogen content is largely prepared and readily used for retarding the methanol permeation in the state-of-the-art commercial Nafion membrane.The high N-content in this porous GDY nanofilm remarkably increases the selective suppression in methanol transfer,and single-layer GDY film can efficiently prevent 43％methanol crossover and the value of the double-layer GDY film can be high up to 69％.The power performance and the long-term stability of the cell are obviously improved due to the reduced methanol crossover.     

Poly(arylene ether sulfone)s containing pendant sulfonic acid groups as membrane materials for direct methanol fuel cells

A series of poly(arylene ether sulfone)s containing pendant sulfonic acid groups have been prepared by an aromatic substitution polymerization reaction using 4,4-difluorodiphenylsulfone, 6,7-dihydroxy-2-naphthalenesulfonate, and various hydroxyl terminated monomers in the presence of potassium carbonate. The synthesized sulfonated polymers have been characterized by nuclear magnetic resonance spectroscopy, Fourier transform infrared spectroscopy, gel permeation chromatography, ion exchange capacity, thermogravimetric analysis, and proton conductivity measurements. With a molecular weight of 50,000–59,000 g/mol and an ion exchange capacity of 1.17 meq./g, these polymers are thermally stable up to 250 °C. They are found to exhibit better performance at 65 and 80 °C in direct methanol fuel cells than Nafion 115 membrane despite lower proton conductivity due to a significantly lower methanol crossover.     

MEA with double-layered catalyst cathode to mitigate methanol crossover in DMFC

Methanol permeation is one of the key problems for direct methanol fuel cell (DMFC) applications. It is necessary to change the structure of the cathode of membrane electrode assembly (MEA). Therefore, a novel MEA with double-layered catalyst cathode was prepared in this paper. The double-layered catalyst consists of PtRu black as inner catalyst layer and Pt black as outer catalyst layer. The inner catalyst layer is prepared for oxidation of the methanol permeated from anode. The results indicate that this double-layered catalyst reduced the effects of methanol crossover and assimilated mixed potential losses. The performance of MEA with double-layered catalyst cathode was 52.2 mW cm⁻², which was a remarkable improvement compared with the performance of MEA with traditional cathode. The key factor responsible for the improved performance is the optimization of the electrode structure.     

Sulfonated poly(ether ether ketone)/poly(amide imide) polymer blends for proton conducting membrane

Poly(amide imide) (PAI) was synthesized using 1,2,4-benzenetricarboxylic anhydride (BTBA) and 4,4′-methylenebis(phenyl isocyanate) (MBPI). SPEEK/PAI blend membranes were prepared and investigated by NMR, GPC, FT-IR and AFM. The chemical structures of PAI and SPEEK were characterized by using NMR and FT-IR. The adsorption of the SPEEK/PAI blend membrane of water or methanol solution was also characterized. The significant swelling of the blend membrane in concentrated methanol solution was explained by the solubility parameter. The water diffusion coefficient (D_H2O) was related to the lambda value of the membrane. The SPEEK/PAI blend membrane had a lower proton conductivity and methanol permeability than Nafion. However, the relative selectivity (proton conductivity divided by methanol permeability) of the SPEEK/PAI 70/30 (w/w) blend membrane was 3.46 × 10⁴ S s cm⁻³, which is closed to that of Nafion (3.30 S s cm⁻³).     

Synthesis and characterization of novel sulfonated naphthalenic polyimides as proton conductive membrane for DMFC applications

To prepare proton conductive membrane for direct methanol fuel cells (DMFC), a novel sulfonated aromatic diamine monomer, 1,4-bis(4-amino-2-sulfonic acid-phenoxy)-benzene (DSBAPB) was synthesized and characterized by ¹H NMR and FT-IR. Then a series of sulfonated polyimides (SPIs) were prepared from DSBAPB with 1,4,5,8-naphthalene tetracarboxylic dianhydride (NTDA) and a non-sulfonated diamine, 4,4′-oxydianiline (ODA) via one-step high-temperature polymerization method. The sulfonation degree of the SPIs can be controlled by changing the mole ratio of sulfonated monomer to non-sulfonated monomer. The obtained SPI membranes exhibit desirable proton conductivity ranged from 7.9 × 10⁻³ to 7.2 × 10⁻² S cm⁻¹ and low methanol permeability of less than 2.85 × 10⁻⁷ cm² s⁻¹. Furthermore, the hydrolysis stability of the obtained SPIs is better than the BDSA based SPIs caused by the flexible structure.     

A method for analysis of DMFC performance curves

Our recent analytical model of direct methanol fuel cell is used to fit experimental performance curves. Based on evolutionary genetic algorithm, a new fitting procedure is developed. The idea is to fit simultaneously a set of performance curves, which have several common fitting parameters. On the first stage of evolution all parameters are determined independently. Starting from certain step a mean values of common parameters are calculated and further evolution corrects the mean values. For different sets of experimental curves the method gives well reproducible results. The physical parameters resulted from fitting and the effect of crossover on cell performance are discussed.     

Studies of Self-assembled Monolayers Formed by Imidazoline on Iron Surface by SEM and SECM

Self-assembled monolayers (SAMs) formed from organic substances can improve the inhibition of metal corrosion, because uniform and closely packed films formed on the metal surface providing an insulating layer1, 2. SAMs on the iron surface are studied so far because iron is one active metal which is easily corroded in the air. In this paper, SECM and SEM have successfully been applied in the study of SAMs inhibition corrosion for iron. SECM has been used to study the electrochemically a…     

Characterization of the effect of REC on the compatibility of PHBH and PLA

This study reports the compatibility of the biobased polymers poly(3-hydroxybutyrate-co-3- -hydroxyhexanoate) (PHBH) and poly(lactic acid) (PLA), as well as the effect of the addition of a reactive epoxy compatibilizer (REC) to the PHBH/PLA blend. The chemical structure, thermal performance, surface morphology and mechanical properties of the blends were measured using fourier transform infrared spectroscopy, differential scanning calorimetry, dynamic thermo-mechanical analysis, thermogravimetric analysis, scanning electron microscopy, and impact and tensile testing.PHBH and PLA were partially compatible, and a PHBH/PLA mass ratio of 80:20 was selected for evaluation with an REC. The REC decreased the difference between the glass-transition temperatures of PHBH and PLA, decreased the particle size of the dispersed phase of the PHBH/PLA blend and produced uniform particle distribution. Moreover, the REC improved the elongation at break and impact strength of the PHBH/PLA blend. These results show that the addition of an REC improves the compatibility of PHBH and PLA.     

纤维素纳米晶体薄膜的制备与表征

讨论了两种新型纤维素纳米晶体(Cellulose nanocrystal,CNC)薄膜的制备方法:浸没法和旋涂法,并利用红外反射吸收光谱(Infrared reflection absorption spectroscopy,IRRAS)和原子力显微镜(Atomic force microscopy,AFM)对其进行表征。AFM高度图显示两种工艺制备的CNC薄膜均由棒状的CNC纳米颗粒交错叠加而成。实验结果显示,旋涂法制备的薄膜更加光滑,粗糙度RMS约为2.7 nm。由于带电颗粒间斥力的存在,浸没法制备的CNC膜厚度最大约为15 nm,而旋涂法可以得到更厚的CNC薄膜,其厚度可达50 nm以上。研究CNC悬浮液浓度与旋涂法CNC膜厚之间的关系后发现,可以通过改变CNC溶液的浓度对薄膜厚度进行控制。IRRAS结果也证实随着CNC悬浮液浓度的增加,旋涂薄膜的厚度随之增加。     

Electrochemical and microscopic studies of surface-confined DNA

We have studied the micropatterning and characterization of the organic monolayers using cyclic voltammetry (CV), scanning electrochemical microscopy (SECM), atom force microscopy, and AC impedance, and have determined the electrochemical parameters, i.e., the apparent reaction rate constant (K _f) and the coverage of the electrode surface (θ). CV and SECM experiments demonstrated that the surface of the modified electrode represents an insulating substrate for ferricyanide. Using the high sensitivity of the electron transfer of ferricyanide to the modification of the gold surface with DNA, we selected this reaction as a probe to study the different modification stages at this modified electrode. SECM images obtained from bare, partially modified, and totally modified electrodes showed very good resolution with different topographies or null according to the extent of modification. Based on a comparison with the results of the experiments, a reasonable agreement can be obtained, which means a conjunction of these techniques.     

Proton exchange membrane using partially sulfonated polystyrene-b-poly(dimethylsiloxane) for direct methanol fuel cell

A diblock copolymer ionomer containing a rubbery poly(dimethylsiloxane) block has been developed as a proton exchange membrane for direct methanol fuel cell (DMFC). The partially sulfonated polystyrene-b-poly(dimethylsiloxane) (sPS-b-PDMS) membrane with 38% sulfonation degree exhibited 3 times lower methanol permeability and 2.6 times higher membrane selectivity (proton conductivity/methanol permeability) compared to Nafion^® 115 at 25 °C. Coexistence of microphase domains and ionic clusters was confirmed from the morphological studies by small-angle X-ray scattering and tapping-mode atomic force microscopy. Gas chromatographic analysis revealed that water/methanol selectivity of sPS-b-PDMS was 20 times higher than that of Nafion^® 115. Such a high water/methanol selectivity can be attributed to the existence of PDMS microdomains minimizing methanol permeation through hydrophilic ion channels. sPS-b-PDMS membranes were fabricated into membrane electrode assembly (MEA), and air-breathing DMFC test for these MEAs showed a better performance compared to the MEA composed of Nafion^® 115.     

甲醇电化学催化氧化机理研究进展

甲醇催化氧化机理的研究对催化剂的开发具有重要的意义。本文概述了甲醇在铂表面催化氧化的反应机理;催化剂的中毒情况以及抗CO催化剂的研究进展,重点阐述了催化剂的结构和表面组成以及电极电势对催化活性的影响。目前的催化剂是不令人满意的．基础研究将有助于避免用纯经验的方法来寻求更为理想的催化剂。     

Nafion膜在直接甲醇燃料电池中的应用及改进

Nafion质子交换膜性能优越,广泛应用于固体聚合物燃料电池中,但因存在甲醇渗透问题,使其在直接甲醇燃料电池中的应用受限制。本文讨论了Nafion质子交换膜的物质传输机理,侧重介绍甲醇分子的渗透机理,综述了基于降低甲醇渗透率而对Nafion膜所做的改进性研究和几种具有应用前景的替代膜。     

A novel process for membrane fabrication: thermally assisted evaporative phase separation (TAEPS)

Poly(vinylidene fluoride) (PVDF) membranes fabricated from conventional processes have a limited range of microstructures. For example, PVDF membranes with spherulitic and isotropic microstructures containing macrovoids are extremely difficult to avoid using standard casting techniques such as wet-casting and thermally induced phase-separation (TIPS) casting. In order to create novel PVDF membrane microstructures such as a spongy, open-celled structure, a new membrane-formation process with six independent process parameters has been developed. Because this new process, thermally assisted evaporative phase separation (TAEPS), has a large number of parameters, the membrane microstructures are easily changed. The TAEPS process can fabricate a PVDF membrane with a spongy, anisotropic microstructure without macrovoids using a simple ternary system with no additives. In addition to studying the novel and unique microstructures available with the TAEPS process, the relationship between final morphology, performance, and processing conditions has been investigated in this paper.     

Synthesis and characterization of novel core-shell colloidal particles ZnO/poly(ethylcyanoacrylate)

Here we report the synthesis and physicochemical characterization of novel hybrid core/shell type ZnO/poly(ethylcyanoacrylate) colloidal particles. It is expected that coating ZnO colloidal particles with biocompatible and biodegradable poly(alkylcyanoacrylates) will pave the way toward the potential application of ZnO colloidal particles in biomedical research. Recent findings of cell selective toxicity indicate a potential utilization of ZnO colloidal particles in the treatment of cancer. For this purpose, ZnO colloidal particles have to be selectively delivered to the site of action by a suitable biocompatible and biodegradable carrier system. Toward this goal, poly(alkylcyanoacrylates) meet ideally the requirements for carrier systems in drug delivery due to their biocompatibility, biodegradability, low toxicity, and ability to overcome the multidrug resistance in cancer cells.     

A novel type of Si-containing poly(urethane-imide)s: synthesis, characterization and electrical properties

A novel type of a Si-containing poly(urethane-imide) (PUI) was prepared by two different methods. In the first method, Si-containing polyurethane (PU) prepolymer having isocyanate end groups was prepared by the reaction of diphenylsilanediol (DSiD) and toluene diisocyanate (TDI). Subsequently the PU prepolymer was reacted with pyromellitic dianhydride (PMDA) or benzophenonetetracarboxylic dianhydride (BTDA) in N-methyl pyrolidone (NMP) to form Si-containing modified polyimide directly. In the second method, PU prepolymer was reacted with diaminodiphenylether (DDE) or diaminodiphenylsulfone (DDS) in order to prepare an amine telechelic PU prepolymer. Finally, the PU prepolymer having diamine end groups was reacted with PMDA or BTDA to form a Si-containing modified polyimide. Cast films prepared by second method were thermally treated at 160 °C to give a series of clear, transparent PUI films. Thermogravimetric analysis indicated that the thermal degradation of PUI starts at 265 °C which is higher than degradation temperature of conventional PU, confirming that the introduction of imide groups improved the thermal stability of PU.To characterize the modified polyimides and their films, TGA, FTIR, SEM and inherent viscosity analyses were carried out. The dielectrical properties were investigated by the frequency-capacitance method. Dielectric constant, dielectric breakdown strength, moisture uptake and solubility properties of the films were also investigated.     

Characterization of polyesters: Thermo-oxidative degradation

The thermo-oxidative degradation ofPET was investigated. Using turbidimetric titration the distribution of molecular mass at different degradation steps was determined. Chemical and molecular transformations of the polymers during degradation were also analyzed. It is shown that vinylic end groups are involved in radical reactions and determine the increase of the molecular mass.

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Characterisierung von Polyestern: Thermo-oxidativer Abbau

Zusammenfassung Es wird der thermo-oxidative Abbau vonPET untersucht. Mit Hilfe der turbidimetrischen Titration wurde die Molekulargewichtsverteilung in unterschiedlichen Stufen des Abbaus bestimmt. Die chemischen und molekularen Umwandlungen des Polymers während der Abbauzeit wurden ebenfalls untersucht. Es wurde festgestellt, daß Vinylester-Endgruppen an Radikal-Reaktionen beteiligt sind und eine Molekulargewichtserhöhung verursachen.

     

Preparation,characterization and application of a novel thermal stable composite nanofiltration membrane

A thermal stable composite membrane was prepared by interfacial polymerization of piperazine (PIP) and trimesoyl chloride (TMC) on poly(phthalazinone ether amide) (PPEA) ultrafiltration membrane. The effect of reaction parameters on the performance of composite membranes was studied and optimized. The surface morphologies of the composite membrane and the substrate were observed by scanning electron microscopy (SEM) and atomic force microscopy (AFM). The rejection of optimized composite membrane for dyes Congo red (CGR) and Acid chrome blue K (ACBK), the molecular weight (MW) of which is over 400, was over 99.2%, with a flux at about 180 L m⁻² h⁻¹. While the rejection for NaCl was only 18.2% with a flux over 270 L m⁻² h⁻¹, when tested at 1.0 MPa 60 °C. The composite membrane was applied in the desalination-purification experiment of dye ACBK and NaCl mixed solution. The flux of the membrane increased obviously as the operation pressure and/or temperature increased, while the rejection for dye was constant and kept over 99.3%. The purification experiments were accomplished effectively at 1.0 MPa, 80 °C. Only after five rounds of desalination-concentration experiment, about 160 min, the salt mixed in dye solution was fully removed. The initial flux of the eighth cycle was about 254 L m⁻² h⁻¹, which was only 20 L m⁻² h⁻¹ lower than that of the first round. The rejection of the membrane was constant and kept over 99.3% through out the eight cycles of purification experiment.     

溶胶-凝胶流动相异型直接甲醇燃料电池性能研究

以掺杂石墨粉的中间相碳微球(MCMB/G)烧结管为阴极支撑体,采用浸涂工艺分别制备了扩散层和催化层并在其外表面包裹Nafion膜,制得管状异型阴极并组装成异型直接甲醇燃料电池;采用溶胶-凝胶法制备了适用于直接甲醇燃料电池的溶胶-凝胶流动相。研究了溶胶-凝胶流动相异型直接甲醇燃料电池的阻抗,考察了阴极支撑体壁厚、阴极扩散层载量、实验温度和溶胶黏度等对电池极化性能的影响。结果表明,异型电池阻抗比传统平板电池大,但活化后电池阻抗明显下降;较低的溶胶黏度和较高的工作温度有利于提高电池性能;支撑体壁厚为1.3 mm、扩散层载量为3.5 mg/cm2时的电极性能最优。