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。     

Nanofiltration of NaCl solutions using a SPPO membrane (BQ01) Part 1. Membrane characterization and separation mechanisms

Results from an experimental investigation of BQ01 nanofiltration (NF) are reported in this paper aiming at delineating the role of process parameters on BQ01 performances. The data highlight the specific behavior of BQ01 membranes in response to solute type and to variations in solution concentration. Variations in permeability and separation factors due to the presence of electrolytes are recorded. It is demonstrated that the concentration polarization cannot explain the observed variations. To elucidate the mechanisms related to this particular membrane, another approach based on conformational properties of polymer coating (sulfonated polyphenylene oxide, SPPO) is proposed and discussed in relation with characterization results. The hypothesis about mechanisms that are developed in this part will be confronted to a series of NF experiments under the same operating conditions but under electric field (ENF) in part 2 of this study.     

Composite Membrane of Sulfonated Poly (phenylene oxide) Doped with Phosphosilicate Gels for Direct Methanol Fuel Cell

Summary The newly developed composite membranes of sulfonated poly (phenylene oxide) (SPPO) doped with phosphosilicate gel were prepared for direct methanol fuel cell (DMFC). SPPO with higher ion exchange capacity (IEC) value (IEC=2.83 mequiv./g) was chosen as polymer matrix, and the phosphosilicate gel with P/Si equal to 1.5 was employed as dopant. Sulfonation of PPO was confirmed by FT-IR and ¹H NMR. And the morphology characterization of sol particles with different stirring time was done by TEM. Moreover, the surface morphology of composite membranes was characterized by SEM. As for methanol permeability (P_M) and proton conductivity (σ), it was demonstrated that all composite membranes were displaying lower methanol permeability than Nafion^?112 and comparable conductivity to Nafion^?112 at room temperature under hydration state. When it comes to selectivity parameter (Φ=σ/P_M), composite membranes show higher Φ values than Nafion^?112, and the highest value is 4.70, 5.6 times higher than 0.845 of Nafion^?112. It is implied that the composite membranes will be the promising membrane material used in DMFC.     

Silicate-based polymer-nanocomposite membranes for polymer electrolyte membrane fuel cells

Proton-exchange membrane fuel cells have emerged as a promising emission free technology to fulfill the existing power requirements of the 21st century. Nafion^® is the most widely accepted and commercialized membrane to date and possesses excellent electrochemical properties below 80 °C, under highly humidified conditions. However, a decrease in the proton conductivity of Nafion^® above 80 °C and lower humidity along with high membrane cost has prompted the development of new membranes and techniques. Addition of inorganic fillers, especially silicate-based nanomaterials, to the polymer membrane was utilized to partially overcome the aforementioned limitations. This is because of the lower cost, easy availability, high hydrophilicity and higher thermal stability of the inorganic silicates. Addition of silicates to the polymer membrane has also improved the mechanical, thermal and barrier properties, along with water uptake of the composite membranes, resulting in superior performance at higher temperature compared to that of the virgin membrane. However, the degrees of dispersion and interaction between the organic polymer and inorganic silicates play vital roles in improving the key properties of the membranes. Hence, different techniques and solvent media were used to improve the degrees of nanofiller dispersion and the physico-chemical properties of the membranes. This review focuses mainly on the techniques of silicate-based nanocomposite fabrication and the resulting impact on the membrane properties.     

Investigation of SPPO Membranes by Positron Annihilation Lifetime Spectroscopy

Positron annihilation lifetime spectroscopy （PALS） is a powerful technique to study the free volume in polymers. The lifetime of ortho-positronium （o-Ps）, a bound state of an electron and a positron, can be used to assess the pore size while the intensity can be used to characterize the number of pores. On the basis of the values of the long-lived o-Ps components in the lifetime spectra, the radii and fractional free volumes in the sulfonated poly （2,6-dimethyl-1,4- phenyleneoxide） （SPPO） membranes with different amounts of LiCl were calculated. It was found that, with the increasing amount of LiCl, the free volume radius and the fractional free volume firstly increased and then decreased. After immersing the membranes in distilled water, the free volume radius and the fractional free volume changed with different water concentrations in the membrane.     

SPPO/SiO2/PWA复合质子交换膜的制备及性能

利用溶胶-凝胶法制备出了SPPO/SiO2/PWA复合质子交换膜,对膜的离子交换容量(IEC)、平均当量重量(EW)、磺化度(SD)、吸水性、溶胀率、质子电导率、Tg进行了表征,此外,还对膜的结构进行了FT-IR、SEM表征,结果表明,所制得的掺杂2%～5%SiO2和3%PWA的SPPO复合膜在100℃、100%相对湿度时的质子电导率与Nafion-117?膜相近,有望作为质子交换膜使用。     

Nanofiltration of NaCl solutions using a SPPO membrane (BQ01) Part 2. Membrane behavior with an electric field

Experimental investigation of electric field enhanced-nanofiltration (called electro-nanofiltration) is reported for sodium chloride solutions. Electro-nanofiltration performance was quantified under several conditions of concentration, electric potential magnitude and polarity. As reported in Part 1 of this study [1], the membrane evaluated, namely BQ01, displayed a different response with respect to pure water and NaCl solution permeation. In this part the influence of various electric fields on BQ01 performance is reported. The other operating parameters are set up identically as the previous study. Electric field application was found to outshine the increase in effective pore size that was usually observed with BQ01 membranes in the presence of electrolytes (without an electric field). As a result, dynamic permeability decreases when an electric field is applied compared to when no electric field is applied. The evolution of the separation factor and pH regarding concentration, electric potentials and polarity were also reported.     

Molecular dynamics simulation analysis of hydration effects on microstructure and transport dynamics in sulfonated poly(2,6-dimethyl-1,4-phenylene oxide) fuel cell membranes

Molecular dynamics simulations were used to study microstructure and transport behavior of hydrated sulfonated poly(2,6-dimethyl-1,4-phenylene oxide) (SPPO) membranes at different hydration levels. Simulation results have shown that SPPO membranes swell upon hydration and become phase segregated into hydrophobic and hydrophilic domains with sulfonic acid groups located at their interface. Evaluation of radial distribution function revealed that with increasing the hydration level, sulfonic acid groups were found to be solvated with more water molecules which cause the sulfonic acid–sulfonic acid and sulfonic acid–hydronium ion distances to increase. By examining the water cluster size distribution, larger well connected clusters containing almost all the water molecules and hydronium ions were formed inside the hydrated SPPO membranes at increased water contents. Furthermore, the calculated hydronium ion and water diffusion coefficients in SPPO based membranes were increased by increasing the hydration level and were smaller than those in Nafion membrane.     

Comparison of the Free Volume of LiCl-Added SPPO Membrane and SPPO-PES Blend Membrane by Positron Annihilation Method

Positron annihilation lifetime spectroscopy （PALS） is a powerful technique for the study of free volume in polymers. The lifetime of ortho-positronium （o-Ps）, a bound state of an electron and a positron, can be used to assess the pore size, while the intensity can be used to characterize the number of pores. Based on the values of the long-lived o-Ps components in the lifetime spectra, the radii and fractional free volumes of sulfonated poly （2,6-dimethyl-1,4- phenyleneoxide） （SPPO） membranes with added LiCl and SPPO-PES （Polyethersulfone） blend were compared. Free volume radii in both kinds of membranes are discussed.     

Polymer membranes for high temperature proton exchange membrane fuel cell: Recent advances and challenges

Proton-exchange membrane fuel cells (PEMFCs) are considered to be a promising technology for efficient power generation in the 21st century. Currently, high temperature proton exchange membrane fuel cells (HT-PEMFC) offer several advantages, such as high proton conductivity, low permeability to fuel, low electro-osmotic drag coefficient, good chemical/thermal stability, good mechanical properties and low cost. Owing to the aforementioned features, high temperature proton exchange membrane fuel cells have been utilized more widely compared to low temperature proton exchange membrane fuel cells, which contain certain limitations, such as carbon monoxide poisoning, heat management, water leaching, etc. This review examines the inspiration for HT-PEMFC development, the technological constraints, and recent advances. Various classes of polymers, such as sulfonated hydrocarbon polymers, acid-base polymers and blend polymers, have been analyzed to fulfill the key requirements of high temperature operation of proton exchange membrane fuel cells (PEMFC). The effect of inorganic additives on the performance of HT-PEMFC has been scrutinized. A detailed discussion of the synthesis of polymer, membrane fabrication and physicochemical characterizations is provided. The proton conductivity and cell performance of the polymeric membranes can be improved by high temperature treatment. The mechanical and water retention properties have shown significant improvement., However, there is scope for further research from the perspective of achieving improvements in certain areas, such as optimizing the thermal and chemical stability of the polymer, acid management, and the integral interface between the electrode and membrane.