Proton conductivity of Nafion/ex situ Stöber silica nanocomposite membranes as a function of silica particle size and temperature

In the first systematic study of the influence of the size of silica particles on ion exchange capacity (IEC) and proton conductivity of Nafion–silica nanocomposite membranes, thin films cast from mixtures of silica particles (5 wt%) with varying diameters ranging from 10 to 400 nm and Nafion in alcohol were examined. IECs decreased exactly as expected with the dilution of Nafion and its sulfonic acid groups with added silica. At 80 °C, the proton conductivity was also less with silica particles. However, at higher temperatures (120 °C), there was a 58 % improvement in proton conductivity at low relative humidity and a 45 % improvement at higher relative humidity for nanocomposite membranes prepared with silica particles <50 nm in size. The improvement was less significant with larger silica particles in the membranes.     

SPPEK/PWA质子导电复合膜的制备与性能

以磺化杂萘联苯聚醚酮(SPPEK)为基体,采用共混法制备了SPPEK/PWA复合质子交换膜。采用红外光谱、热分析与交流阻抗等方法对复合膜的结构和性能进行了研究,并与Nafion117膜进行了比较。结果表明,磷钨酸(PWA)的掺杂使得复合膜的吸水率和溶胀度增大,同时热稳定性能得到提高。复合膜在20℃时的质子电导率为0.67×10-2S/cm,接近Nafion117膜的质子电导率(1.08×10-2S/cm)。且随着温度的升高,电导率逐渐增大,最高可达1.18×10-2S/cm。此外,对复合膜不同方向上的电导率进行了测试,表明膜平面方向上的电导率(8.10×10-2S/cm)高于厚度方向上电导率(7.50×10-3S/cm)约一个数量级。     

Self‐Healing Proton‐Exchange Membranes Composed of Nafion–Poly(vinyl alcohol) Complexes for Durable Direct Methanol Fuel Cells

Proton‐exchange membranes (PEMs) that can heal mechanical damage to restore original functions are important for the fabrication of durable and reliable direct methanol fuel cells (DMFCs). The fabrication of healable PEMs that exhibit satisfactory mechanical stability, enhanced proton conductivity, and suppressed methanol permeability via hydrogen‐bonding complexation between Nafion and poly(vinyl alcohol) (PVA) followed by postmodification with 4‐carboxybenzaldehyde (CBA) molecules is presented. Compared with pure Nafion, the CBA/Nafion–PVA membranes exhibit enhanced mechanical properties with an ultimate tensile strength of ≈20.3 MPa and strain of ≈380%. The CBA/Nafion–PVA membrane shows a proton conductivity of 0.11 S cm^?1 at 80 °C, which is 1.2‐fold higher than that of a Nafion membrane. The incorporated PVA gives the CBA/Nafion–PVA membranes excellent proton conductivity and methanol resistance. The resulting CBA/Nafion–PVA membranes are capable of healing mechanical damage of several tens of micrometers in size and restoring their original proton conductivity and methanol resistance under the working conditions of DMFCs. The healing property originates from the reversibility of hydrogen‐bonding interactions between Nafion and CBA‐modified PVA and the high chain mobility of Nafion and CBA‐modified PVA.     

Sulfonated carbon black-based composite membranes for fuel cell applications

Two different commercial grade carbon black samples, Cabot Regal 400R (C1) and Cabot Mogul L (C2), were sulfonated with diazonium salt of sulfanilic acid. The resultant sulfonated carbon black samples (S–C) were characterized by Fourier transform infrared spectroscopy (FTIR) and thermal gravimetric analysis (TGA). Composite membranes were then prepared using S–C as fillers and sulfonated poly(ether ether ketone) (SPEEK) as polymer matrix with three different sulfonation degrees (DS = 60, 70 and 82%). Structure and properties of the composite membranes were characterized by FTIR, TGA, scanning electron microscopy, proton conduction, water uptake, ion exchange capacity and chemical stability. Incorporation of S–C particles above 0· 25 wt% caused decrease in chemical stability. Pristine and composite membranes prepared from SPEEK82 decomposed completely in $\boldsymbol{<}$ 1 h, which is undesirable for fuel cell applications. SPEEK60 membrane having wt% of 0·25–0· 5 with S–C particles led to higher proton conductivity than that of pristine membrane. No positive effect was observed on the properties of the composite membranes with the addition of S–C particles at high concentrations due to the agglomeration problems and decrease in the content of conductive polymer matrix.     

PWA/silica/PFSA composite membrane for direct methanol fuel cells

A novel composite membrane was prepared by incorporation of silica-included phosphotungstic acid (PWA) additive into perfluorosulfonic acid (PFSA) followed by solution casting. Physico-chemical properties of the composite membranes were studied by Fourier transform infrared (FT-IR) spectroscopy, thermogravimetry analysis (TGA), water uptake and swelling ratio. The results of FT-IR and TGA illustrated the stability of the PWA-silica additive in the PFSA matrix. Lower PWA-silica additive loading (2.5 and 5 wt%) in the composite membranes helped to inhibit methanol crossover and enhance the proton conductivity. However, higher additive content shows decrease in both methanol resistance and proton conductivity.     

全钒液流电池用新型全氟磺酸离子交换膜制备及性能研究

通过溶液流延成膜法制备了具有不同离子交换容量(IEC)的全氟磺酸(PFSA)离子交换膜,并测试了其吸水率、电导率、钒离子(Ⅴ(Ⅳ))透过率和选择性系数。研究发现,具有高IEC值的PFSA离子交换膜具有相对较低的Ⅴ(Ⅳ)离子透过率和较高的质子电导率。其中IEC值为1.10mmol/g的PFSA离子交换膜对Ⅴ(Ⅳ)离子具有最高的选择性,其选择性系数为Nafion 117膜的2.97倍。     

聚乙烯醇-聚丙烯酸共混膜的阻醇及质子导电性能研究

针对目前直接甲醇燃料电池 (DMFC)中普遍使用的Nafion系列全氟磺酸膜存在的甲醇穿透问题 ,制备了在渗透蒸发醇 -水分离领域有良好分离效果的聚乙烯醇 (PVA)和聚乙烯醇 -聚丙烯酸 (PVA -PAA)共混膜并研究了其阻醇和质子导电性能 .与Nafion1 1 7膜相比 ,PVA膜和PVA -PAA共混膜的阻醇性能有明显提高 ,其导电能力虽很大程度上依赖于外加电解质溶液 ,但PAA的混入使PVA膜材料的导电性能有了很大改善     

PVA-PWA-Al2O3无机-有机复合质子交换膜的研究

以聚乙烯醇(PVA)、磷钨酸(PWA)和氧化铝(Al2O3)溶胶为原料,制备得到PVA-PWA-Al2O3无机-有机复合质子交换膜,测定了膜的电导率、含水率、溶胀度和甲醇透过系数等性质.测试结果表明,该复合膜具有较高的导电率和较好的阻醇效果,室温下测得电导率最高达到1.162 S/cm,甲醇透过系数在10-7cm2/s左右.复合膜中PWA含量增加,膜的电导率、含水率、溶胀度和甲醇透过系数都有所上升;膜中Al2O3含量增加,膜的电导率、含水率、溶胀度提高,但甲醇渗透系数稍有下降.     

磺化聚酰亚胺/SiO2复合膜的制备及其质子交换性能研究

制备了具有不同硅含量的磺化聚酰亚胺/二氧化硅(SPI/SiO2)复合膜,研究了SiO2的引入对复合膜的力学性能、耐热性能、尺寸稳定性以及抗氧化和耐水解稳定性的影响规律,并对其质子传导率和甲醇渗透率进行了评价。结果表明,与商业化的Nafion115膜相比,复合膜表现出更优异的阻醇特性和选择透过性,其中SPI/SiO2-2复合膜具有更突出的高温质子传导特性。     

Synthesis and properties of sulfonated polyimide–polybenzimidazole copolymers as proton exchange membranes

Chemical stability of polymer electrolyte membranes (PEMs) is the key factor affecting the lifetime of fuel cells. It is greatly desirable to develop the PEMs with both high proton conductivity and excellent chemical stability. In this study, a series of sulfonated polyimide–polybenzimidazole copolymers (SPI-co-PBIs) are synthesized via random condensation polymerization of 1,4,5,8-naphthalene tetracarboxylic dianhydride, 4,4′-bis(4-aminophenoxy)biphenyl-3,3′-disulfonic acid, and an amine-terminated polybenzimidazole oligomer. The ion exchange capacities of the resulting SPI-co-PBIs are in the range 1.90–2.47 meq g^?1. Under fully hydrated condition, the SPI-co-PBI membranes show higher proton conductivities than Nafion112. It is found that the incorporation of a small fraction of PBI moiety into the polyimide structure resulted in significant improvement in radical oxidative stability. For example, the SPI-co-PBI-19/1 containing 5 mol % PBI moiety shows only 0.6 wt% weight loss after being soaked in the Fenton’s reagent (3 % H₂O₂ + 3 ppm FeSO₄) at 80 °C for 150 min, whereas the corresponding benzimidazole group-free sulfonated polyimide is completely dissolved in the Fenton’s reagent at 80 °C for 140 min. The SPI-co-PBI membranes also show excellent hydrolytic stability due to the highly stable ladder structure of the benzimidazobenzisoquinolinone linkages.     

Decoration of carbon nanotube with SiO2 nanoparticles to improve polyelectrolyte membrane performance

To overcome the poor mechanical performance and the low proton conductivity at high temperature (> 80 degrees C) which hinder the utilization of Nafion membranes for use in PEM Fuel Cell, SiO2 nanoparticle decorated multi-walled carbon nanotubes (MWCNTs) were developed to reinforce both the mechanical property and the water retention capability of Nafion membranes. Results show that the composite membrane is approximately 10% and 5-10% higher than that of recast Nafion membrane in proton conductivity and water retention, respectively. These could be explained by the bifunction of SiO2 which performs both hydrophilicity and proton conductivity. In addition, the mechanical performance was greatly enhanced in the presence of SiO2 decorated MWCNTs.     

Nafion and modified-Nafion membranes for polymer electrolyte fuel cells: An overview

Polymer electrolyte fuel cells (PEFCs) employ membrane electrolytes for proton transport during the cell reaction. The membrane forms a key component of the PEFC and its performance is controlled by several physical parameters, viz. water up-take, ion-exchange capacity, proton conductivity and humidity. The article presents an overview on Nafion membranes highlighting their merits and demerits with efforts on modified-Nafion membranes. Energy security refers to various security measures that a given nation, or the global community as a whole, must carryout to maintain an adequate energy supply     

燃料电池用新型质子交换膜的研究进展

质子交换膜燃料电池(PEMFC)以其高效、清洁、高能量密度和高功率密度等诸多优点正引起人们越来越多的关注和研究．目前,质子交换膜是制约PEMFC技术应用的一个主要问题．为此,开发性能良好、成本经济的新型质子交换膜是一项很有意义的工作、综述了近几年国内外在新型质子交换膜(包括全氟磺酸膜、部分含氟磺酸膜、非氟质子交换膜)方面的研究进展．     

A DNA‐Threaded ZIF‐8 Membrane with High Proton Conductivity and Low Methanol Permeability

Natural biomolecules have potential as proton‐conducting materials, in which the hydrogen‐bond networks can facilitate proton transportation. Herein, a biomolecule/metal–organic framework (MOF) approach to develop hybrid proton‐conductive membranes is reported. Single‐strand DNA molecules are introduced into DNA@ZIF‐8 membranes through a solid‐confined conversion process. The DNA‐threaded ZIF‐8 membrane exhibits high proton conductivity of 3.40 × 10^?4 S cm^?1 at 25 °C and the highest one ever reported of 0.17 S cm^?1 at 75 °C, under 97% relatively humidity, attributed to the formed hydrogen‐bond networks between the DNA molecules and the water molecules inside the cavities of the ZIF‐8, but very low methanol permeability of 1.25 × 10^?8 cm² s^?1 due to the small pore entrance of the DNA@ZIF‐8 membranes. The selectivity of the DNA@ZIF‐8 membrane is thus significantly higher than that of developed proton‐exchange membranes for fuel cells. After assembling the DNA@ZIF‐8 hybrid membrane into direct methanol fuel cells, it exhibits a power density of 9.87 mW cm^?2 . This is the first MOF‐based proton‐conductivity membrane used for direct methanol fuel cells, providing bright promise for such hybrid membranes in this application.     

Intumescent flame retardant polyurethane/reduced graphene oxide composites with improved mechanical, thermal, and barrier properties

Intumescent flame retardant polyurethane (IFRPU) composites were prepared in the presence of reduced graphene oxide (rGO) as synergism, melamine, and microencapsulated ammonium polyphosphate. The composites were examined in terms of thermal stability (both under nitrogen and air), electrical conductivity, gas barrier, flammability, mechanical, and rheological properties. Wide-angle X-ray scattering and scanning electron microscopy indicated that rGO are well-dispersed and exfoliated in the IFRPU composites. The limiting oxygen index values increased from 22.0 to 34.0 with the addition of 18 wt% IFR along with 2 wt% rGO. Moreover, the incorporation of rGO into IFRPU composites exhibited excellent antidripping properties as well as UL-94 V0 rating. The thermal stability of the composites enhanced. This was attributed to high surface area and good dispersion of rGO sheets induced by strong interactions between PU and rGO. The oxygen permeability, electrical, and viscoelasticity measurements, respectively, demonstrated that rGO lead to much more reduction in the gas permeability (by ~90 %), high electrical conductivity, and higher storage modulus of IFRPU composites. The tensile strength, modulus, and shore A remarkably improved by the incorporation of 2.0 wt% of rGO as well.     

Improving the thermal and mechanical properties of silicone polymer by incorporating functionalized graphene oxide

Functionalized graphene oxide (FGO) was produced by reacting graphene oxide nanosheets with vinyl trimethoxy silane (VTMS). The results confirmed the attachment of VTMS molecules to the surface of GO sheets by Si–O–C bonding. The introduction of VTMS molecules led to an excellent dispersibility in tetrahydrofuran and to the complete exfoliation of FGO with a thickness of about 1.19 nm. Meanwhile, FGO/silicone polymer composites were prepared by solution blending method. The incorporation of 0.5 wt% of FGO in silicone polymer improved remarkably the thermal stability, tensile strength, and thermal conductivity of the silicone polymer composite, due to the homogeneous dispersion of FGO in the composites as well as to the strong interfacial adhesion with silicone polymer matrix. Tensile strength and thermal conductivity of the FGO/silicone polymer composite were increased by 95.6 and 78.3 %, respectively, with the addition of 0.5 wt% FGO. The 5 % weight loss temperature of the composite at 0.5 wt% FGO loading was detected 26.1 °C higher than that of silicone polymer.     

Synthesis and characterization of poly(ether sulfone ether ketone ketone) grafted poly(sulfopropyl methacrylate) for proton exchange membranes via atom transfer radical polymerization

A series of copolymers of poly(ether sulfone ether ketone ketone) grafted poly(sulfopropyl methacrylate) (PESEKK-g-PSPMA) were successfully synthesized by atom transfer radical polymerization (ATRP) of sulfopropyl methacrylate (SPMA) after chloromethylation of poly(ether sulfone ether ketone ketone) (PESEKK) backbone. The structure of the chloromethyl PESEKK and the copolymers were carefully investigated. Variation of the polymerization time leads to the formation of copolymers with different degree of sulfonation (DS). The properties of the proton exchange membranes such as water uptake, ion exchange capacity, proton conductivity, and methanol permeability are studied with compared to those of Nafion 117 membranes and could be modulated simply by control of the ATRP time. The copolymers exhibited much lower methanol permeability and higher proton conductivity as compared with Nafion 117.     

Nafion/silane nanocomposite membranes for high temperature polymer electrolyte membrane fuel cell

The polymer electrolyte membrane fuel cell (PEMFC) has been studied actively for both potable and stationary applications because it can offer high power density and be used only hydrogen and oxygen as environment-friendly fuels. Nafion which is widely used has mechanical and chemical stabilities as well as high conductivity. However, there is a drawback that it can be useless at high temperatures (> or = 90 degrees C) because proton conducting mechanism cannot work above 100 degrees C due to dehydration of membrane. Therefore, PEMFC should be operated for long-term at high temperatures continuously. In this study, we developed nanocomposite membrane using stable properties of Nafion and phosphonic acid groups which made proton conducting mechanism without water. 3-Aminopropyl triethoxysilane (APTES) was used to replace sulfonic acid groups of Nafion and then its aminopropyl group was chemically modified to phosphonic acid groups. The nanocomposite membrane showed very high conductivity (approximately 0.02 S/cm at 110 degrees C, <30% RH).     

Fabrication of a proton exchange membrane via blended sulfonimide functionalized polyamide

A novel linear non-fluorinated sulfonimide functionalized polyamide (SPA) polymer electrolyte was successfully synthesized via an aromatic sulfonimide monomer with superior thermal stability and superacidity. The aromatic sulfonimide remains stable below 220 °C. To fabricate membranes with strong mechanical strength and dimensional stability, the polymer was blended with various quantities of PVdF. The PVdF/SPA blend membranes exhibit an excellent capacity of water uptake and high dimensional stability. However, their proton conductivity was found to be substantially lower than that of Nafion 211. Analysis on the SEM images of the PVdF/SPA blend membranes reveals that the low proton conductivity is primarily caused by the large pore structures (>1 μm), which lead to breakdown of the continuous proton transport channels.     

Synthesis and characterization of polystyrene-poly(arylene ether sulfone)-polystyrene triblock copolymer for proton exchange membrane applications

The polystyrene-poly(arylene ether sulfone)-polystyrene (PS-PAES-PS) coil-semirod-coil triblock copolymer was synthesized by the condensation reaction of PS-COCI and H2N-PAES-NH2 telechelic polymers. The reaction was facile characterized by high yields with a perfect control over the block lengths. Following a known reaction protocol it was possible to selectively sulfonate the PS block of the triblock copolymer that led to the sulfonated copolymer sPS-PAES-sPS. Studies on its proton conductivity and methanol permeability were carried out to evaluate its use as the proton exchange membrane in direct methanol fuel cells. Proton conductivity of the membranes was increased depending on the sulfonic acid group content in the sulfonated polymer. The membranes exhibited good dimensional and thermal stability, and low methanol permeability compared to Nafion 117.