Proton conductivity and morphology of new composite membranes based on zirconium phosphates,phosphotungstic acid,and silicic acid for direct hydrocarbon fuel cells applications

The effect of Phosphotungstic acid (PWA) on the proton conductivity and morphology of zirconium phosphate (ZrP), porous polytetrafluoethylene (PTFE), glycerol (GLY) composite membrane was investigated in this work. The composite membranes were synthesized using two approaches: (1) Phosphotungstic acid (PWA) added to phosphoric acid and, (2) PWA + silicic acid were added to phosphoric acid. ZrP was formed inside the pores of PTFE via the in situ precipitation. The membranes were evaluated for their morphology and proton conductivity. The proton conductivity of PWA–ZrP/PTFE/GLY membrane was 0.003 S cm^?1. When PWA was combined with silicic acid, the proton conductivity increased from 0.003 to 0.059 S cm^?1 (became about 60% of Nafion’s). This conductivity is higher than the proton conductivity of Nafion–silica–PWA membranes reported in the literature. The SEM results showed a porous structure for the modified membranes. The porous structure combined with this reasonable proton conductivity would make these membranes suitable as the electrolyte component in the catalyst layer for direct hydrocarbon fuel cell applications.     

Fabrication and characterization of PFSI/ePTFE composite proton exchange membranes of polymer electrolyte fuel cells

PFSI/ePTFE composite proton exchange membranes were fabricated by impregnating perfluorosulfonic acid resin (PFSI resin, Nafion) into chemically modified expanded PTFE (ePTFE) matrix. Chemical modification of sodium-naphthalene treatment and N-methylol acrylamide (NMA) grafting decreased the contact angle of the as-received ePTFE from 125 ± 0.5° to 67 ± 0.5°, effectively converting the as-received hydrophobic ePTFE to a hydrophilic ePTFE matrix. The composite membrane fabricated with the hydrophilic ePTFE have higher impregnated PFSI loading, much lower porosity and better PTFE/PFSI interface contact, as compared to the composite membranes with the as-received ePTFE. This leads to much lower gas permeability and significantly improves the durability under an accelerated dry/wet cycle test. The fuel cell made from the PFSI/ePTFE composite membranes with hydrophilic ePTFE showed superior performance as compared to that with the composite membrane made from the as-received ePTFE and Nafion 211 membrane.     

The study of PTFE/Nafion/Silicate membranes operating at low relative humidity and elevated temperature

The performance and stability of PTFE/Nafion/Silicate composite membranes (PNS membrane) were studied at low and medium operating temperatures with different humidity, and compared with the Nafion112 membrane at the same conditions. The PNS membrane was prepared by impregnation of PTFE/Nafion composite membrane via sol-gel process with TEOS (tetraethoxysilane). When operated cell at low temperature of 60 °C with 100% R.H. humidified H₂/O₂ gases, the PNS membrane performs better than Nafion112, with 1.0, and 0.4 W/cm², respectively. When operated cell at 60 °C with 37% R.H. humidified gases, the discharge stability of PNS membrane is stable than that of Nafion112, this is due to that silicate could hold more water in the PNS membrane at low relative humidity. While the inlet of cell gases temperature keeps at 80 °C, the cell temperature varied 90, 100, and 110 °C, with 20 psig back pressure, their relative humidities were 67, 48 and 33%, respectively. The stability of discharge current remains constant except in the case of cell temperature being as high as 110 °C. It is believed that silicate could hold water except in the case of cell temperature at 110 °C, which is resulted as the membrane dehydration. On the other hand, the Nafion112 cannot operate at low humidity with cell temperature higher than 80 °C owing to membrane dehydration. The silica modified PTFE/Nafion membrane shows the improving cell performance at lower relative humidity due to adsorbed water inside the membrane and catalyst layer.     

不同中空纤维膜材料对烟气中二氧化硫的吸收性能影响

膜法烟气脱硫能耗低、传质面积大、分离效率高,可以有效地解决传统塔器内的液泛、漏液、夹带等问题。本文采用自制的中空纤维膜接触器,通过改变烟气流量、水流量和水温对比了聚四氟乙烯（PTFE）、聚偏氟乙烯（PVDF）和聚丙烯（PP）这3种中空纤维膜对烟气中二氧化硫的吸收性能,并通过电镜和接触角仪表征,对比了3种膜的参数和疏水性。结果表明：在不同烟气流量、水量和水温下,3种膜的吸收性能都表现为PTFE＞PP＞PVDF,120min时二氧化硫吸收浓度,PTFE最大,是PP的1.68倍,是PVDF的4.62倍;烟气流量的改变对二氧化硫的吸收浓度有显著影响,当烟气流量由60mL/min提高到140mL/min时,120min时PTFE膜二氧化硫的吸收浓度提高了2.14倍;影响膜性能的主要因素为疏水性,PTFE浸泡前后的表面接触角为105°和97°,疏水性远大于PP和PVDF。PTFE中空纤维膜孔径大、孔隙率高,具有极强的疏水性,在烟气脱硫及相关吸收过程中表现出较好的应用前景。     

Supported Electrospun Ultrafine Fibrous Poly(tetrafluoroethylene)/ZnO Porous Membranes and their Photocatalytic Applications

Supported photocatalytic poly(tetrafluoroethylene) (PTFE)/ZnO porous membranes were prepared by sintering electrospun PTFE/poly(vinylalcohol)/zinc acetate dehydrate composite membranes. Electrospun PTFE membranes were utilized as supports with excellent chemical stability and high specific surface area, while the photocatalyst‐ZnO particles derived from the thermal decomposition of zinc acetate dehydrate were homogeneously immobilized on the surface of ultrafine PTFE fibers. The PTFE/ZnO membranes could be easily recovered and reused after water treatment. PTFE/ZnO membranes are expected to have a wide range of potential applications in photocatalysis and photocatalysis‐membrane reactors, playing the role of a catalyst as well as a selective barrier against contaminants of interest.     

基于仿生矿化的PTFE中空纤维膜亲水改性研究

由于聚四氟乙烯(PTFE)材料具有强疏水性和极低的表面能,使得PTFE中空纤维膜润湿性差,难以处理水性溶液,限制了其应用过程和领域,因此开展PTFE中空纤维膜亲水化改性研究具有重要的现实意义。利用仿生矿化技术对PTFE中空纤维膜进行表面改性,研究了不同矿化工艺对膜亲水性能的影响,并对改性前后PTFE中空纤维膜的官能团、水通量、气通量、孔径及孔径分布进行了表征。研究表明,仿生矿化能够提高PTFE中空纤维膜的亲水性和水通量,同时由于碳酸钙分子进入膜孔内部,使孔径分布更加均匀,平均孔径和气通量减小。     

Preparation and testing of polyvinyl alcohol composite membranes for reverse osmosis

Thin film composite membranes were prepared by coating porous polysulfone membranes with a polyvinyl alcohol layer and further cross-linking its surface. The thin layer of cross-linked polyvinyl alcohol served as a selective membrane. The membranes were prepared under various conditions and tested for sodium chloride separation. A high sodium chloride separation was achieved but the permeation rate was low compared with commercially available thin film composite membranes. Resistance against the flow of solvent water and sodium chloride solute were determined for individual component barrier layers.     

Performance of EDLCs using Nafion and Nafion composites as electrolyte

We present the electrochemical performance of solid-state EDLCs constructed using composites of perfluorosulfonic acid polymer (Nafion) with micro porous polytetrafluoroethylene (PTFE) membrane and with cellulose acetate (CA), as electrolyte with carbon as electrodes (surface area: 260 m² g⁻¹). The performance is compared with EDLCs constructed with perfluorosulfonic acid polymer as electrolyte. Scanning electron microscopy is used to study the morphology of the composite electrolyte while micro-Raman and IR measurements determine the integrity of the composite. The performance of the EDLC with perfluorosulfonic acid and PTFE composite electrolyte is good and comparable with the performance of the EDLC with pure perfluorosulfonic acid polymer electrolyte. A specific capacitance of 16 F g⁻¹ is obtained for this EDLC with a maximum working potential of 2.0 V. There is an increase in the equivalent series resistance value from 0.08 Ω for the Nafion EDLC to 4.1 Ω for the Nafion/PTFE composite EDLC. However, the performance of the EDLC with the composite of Nafion/CA is poor due to substantial increase in ESR. The probable reasons are discussed.     

Fabrication and characterization of poly(vinylidene fluoride)–polytetrafluoroethylene composite membrane for CO2 absorption in gas–liquid contacting process

The wetting resistance of poly(vinylidene fluoride) (PVDF) membrane is a critical factor which determines the carbon dioxide (CO₂) absorption performance of the gas–liquid membrane contactors. In this study, the composite PVDF–polytetrafluoroethylene (PTFE) hollow fiber membranes were fabricated through dry-jet wet phase-inversion method by dispersing PTFE nanoparticles into PVDF solution and adopting phosphoric acid as nonsolvent additive. Compared with the PVDF membrane, the composite membranes presented higher CO₂ absorption flux due to their higher effective surface porosity and surface hydrophobicity. The composite membrane with addition of 5 wt % PTFE in the dope gained the optimum CO₂ absorption flux of 9.84 × 10⁻⁴ and 2.02 × 10⁻³ mol m⁻² s⁻¹ at an inlet gas (CO₂/N₂ = 19/81, v/v) flow rate of 100 mL min⁻¹ by using distilled water and aqueous diethanolamine solution, respectively. Moreover, the 5% PTFE membrane showed better long-term stability than the PVDF membrane regardless of different types of absorbent, indicating that polymer blending demonstrates great potential for gas separation. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47767.     

Carbon Nanotubes Based Nafion Composite Membranes for Fuel Cell Applications

Carbon nanotubes (CNTs) containing Nafion composite membranes were prepared via melt‐blending at 250 °C. Using three different types of CNTs such as pure CNTs (pCNTs), oxidised CNTs (oCNTs) and amine functionalised CNTs (fCNTs); the effect of CNTs surface oxidation as well as functionalisation in composite membranes was investigated by focussing on three aspects: thermo‐mechanical stability, thermal degradation and proton conductivity. The oCNTs‐containing Nafion composite membrane exhibited concurrent improvement in most of the properties as compared to that of pure Nafion or other CNTs‐containing Nafion composite membranes.     

Novel Nafion/Hydroxyapatite composite membrane with high crystallinity and low methanol crossover for DMFCs

Summary Novel Nafion/Hydroxyapatite (HA) composite membrane with high crystallinity was fabricated to suppress methanol crossover for direct methanol fuel cell (DMFC) applications. In this study, water and methanol diffusivity were evaluated through water-methanol sorption/desorption test and methanol permeation experiments. It was shown that the water-methanol diffusivity and methanol crossover for the composite membranes decrease as HA increases. Structural variation was investigated with wide-angle x-ray. As a result, it was found that the crystallinity of composite membranes increases with HA whereas water uptake content decreases gradually. Methanol permeability using a diffusion cell reduced in the composite membranes, suggesting that high crystallinity and low water uptake of composite membrane result in the suppression of methanol crossover due to the incorporation of HA into Nafion structure.     

Nafion/PTFE Composite Membranes for Fuel Cell Applications

The composite membranes were prepared by impregnation of porous poly(tetrafluoroethylene) membranes with a 5 wt% Nafion solution. Scanning electron microscope micrographs of composite membranes show the surface and cross section of poly(tetrafluoroethylene) membranes were covered and filled with Nafion resin. Comparison of physical properties and fuel cell performance of composite membranes with those of Nafion membranes (DuPont Co) is presented. The composite membrane has better thermal stability and gas barrier property but worse ionic conductivity than Nafion membrane. Though the composite membrane has a lower conductivity than Nafion membrane, however, owing to the thinner thickness of composite membrane (in thickness of 20±5µm) than Nafion-115 (in thickness of 125µm) and Nafion-117 (in thickness of 175µm) membranes, the composite membrane has a shorter H⁺ ion transporting pathway and thus a higher conductance (conductance = conductivity/membrane thickness) than Nafion-115 and Nafion-117 membranes. Thus the composite membrane has a better fuel cell performance than Nafion-117 and Nafion-115 membranes. In this report, we show that our composite membrane has a fuel cell performance similar to Nafion-112 membrane (in thickness of 50µm).     

Formation and analysis of a polyimide layer in composite membranes

Composite membranes containing a thin‐film layer of aromatic polyimides (PI) ensure an advantageous combination of selectivity and permeability in gas separation. A series of rigid‐chain PI with different chemical structures were studied as a thin active layer. Composite membranes were prepared by coating a solution of poly(amic acid) (PAA) and an imidization catalyst on a poly(phenylene oxide) (PPO) support with pores filled by decane. The subsequent stage of solid‐state catalytic transformation of the PAA/PPO membrane into the PI/PPO membrane determines the specific structure of the PI layer and the transport properties of the PI/PPO composite membranes. The structure of composite membranes was determined by scanning electron microscopy and analyzed in the terms of the resistance model of gas transport in composite membranes. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 75: 1026–1032, 2000     

Influence of ligands of palladium complexes on palladium/Nafion composite membranes for direct methanol fuel cells by supercritical CO2 impregnation method

Palladium/Nafion composite membranes were synthesized by supercritical impregnation method to reduce methanol crossover in direct methanol fuel cells. The palladium complexes used in this study were palladium(II) acetylacetonate, palladium(II) hexafluoroacetylacetonate, and palladium (II) bis(2,2,6,6-tetramethyl-3,5-heptane-dionato). The palladium complexes with various loading amounts from 0.010 to 0.050 g in a high-pressure vessel were dissolved in supercritical CO₂, and impregnated into Nafion membranes.The SEM images indicated that the palladium complexes were successfully deposited into Nafion membrane, and there were no problems such as cracking and pinhole. The EDX analysis showed that the palladium particles were distributed both at the membrane surface and also extended deeper into the membrane. The TEM images indicated that thin dense band of agglomerated Pd particles can be observed near the membrane surface, and a significant number of isolated Pd particles can be seen deeper into the membrane, when Pd(II) acetylacetonate was used as palladium complex. When palladium(II) hexafluoroacetylacetonate and palladium (II) bis(2,2,6,6-tetramethyl-3,5-heptane-dionato) were used, dense band of agglomerated Pd particles cannot be observed near the membrane surface, and small Pd particles were observed inside the membranes.The XRD analysis indicated that the crystalline peak of Nafion membrane at 2θ = 17° increased with the supercritical CO₂ treatment. It means that the degree of crystallinity for Nafion membrane increased by supercritical CO₂. The metal Pd peak at 2θ = 40° was observed for the Pd/Nafion membranes.The methanol crossover was reduced and the DMFC performance was improved for the Pd/Nafion membranes compared with Nafion membrane at 40 °C. The successful preparation of Pd/Nafion membranes by supercritical CO₂ demonstrated an effective alternative way for modifying membranes and for depositing electrode catalytic nanoparticles onto electrolyte.     

氧化石墨烯/磺化聚苯并咪唑高温质子交换膜的制备和表征

通过共混法和原位聚合法成功制备氧化石墨烯（GO）/磺化聚苯并咪唑（SPBI）质子交换复合膜。用FTIR及TEM表征了复合膜的结构,并测试了复合膜的热稳定性、力学性能、尺寸稳定性、含水率、酸掺杂率、氧化稳定性及质子电导率,重点考察不同制备方法、GO的加入对GO/SPBI质子交换复合膜结构和性能的影响。实验结果表明,GO在Y-GO/SPBI-1%复合膜中呈薄片状并良好分散。添加GO后复合膜的力学性能大幅提高,拉伸强度相较于Nafion 117膜（26.65MPa）提高了2.5倍。Y-GO/SPBI-1%复合膜热稳定性稍高于G-GO/SPBI-1%复合膜。Y-GO/SPBI-1%复合膜拥有与SPBI膜相当的含水率,比G-GO/SPBI-1%复合膜的含水率提高了51.36%,表明原位聚合法制备的膜具有良好的保水能力。原位聚合法制备的复合膜具有更高的酸掺杂率和更低的酸溶胀度,提高了膜的尺寸稳定性。Y-GO/SPBI-1%质子交换复合膜在相对湿度40%、160℃下具有最高的质子电导率0.113S/cm。GO上的含氧官能团有助于复合膜中质子的跳跃,原位聚合法使GO更均匀地分散在SPBI基质中,对复合膜质子电导率的提高起到关键作用。     

Zeolite-based composite membranes for high temperature direct methanol fuel cells

Composite Nafion membranes containing three natural zeolites (Mordenite, Chabazite and Clinoptilolite) were prepared by using a recast procedure for application in high temperature Direct Methanol Fuel Cells (DMFCs). The Nafion-zeolite membranes have shown good properties for high temperature DMFC application, due to their improved water retention characteristics. A maximum power density of 390 mW cm^–2 was achieved at 140 °C with the mordenite-based composite membranes in the presence of oxygen feed. The electrochemical behaviour of the composite membranes was interpreted in the light of surface properties and acidic characteristics of the fillers.     

Water recovery from flue gas using polyether block amide 2533/sulfonated poly(ether ether ketone) composite membrane

Recycling water from flue gas of coal-fired power plants is of great significance to save energy and water resources and reduce environmental pollution. In the present work, two potential polymers (polyether block amide 2533(PEBAX 2533) and sulfonated poly(ether ether ketone) (SPEEK)) were investigated and showed high water vapor permeability and selectivity, respectively. Combined with the advantages of the two materials, a novel PEBAX 2533/SPEEK composite membrane with an ultra-thin SPEEK selection layer on the outer surface of the high permeable PEBAX 2533 layer was prepared by dip coating. The composite membranes were assembled into a membrane capsule module and tested directly in artificial and real flue gas. The condensed water vapor fluxes were 1006.9 g/m².h in artificial flue gas and 600–900 g/m².h on average in real flue gas during a period of 30 days, exhibiting good water vapor permeability and durability in real flue gas.     

Thin film composite nanofiltration membranes with polystyrene sodium sulfonate–polypiperazinetrimesamide semi-interpenetrating polymer network active layer

The present work depicts the preparation, characterization, and application of thin film composite nanofiltration (TFCNF) membranes. TFCNF membranes having polyacrylonitrile ultrafiltration support with active layer made of polystyrene sodium sulfonate–polypiperazinetrimesamide semi-interpenetrating polymer network (semi-IPN) are prepared. Membranes with semi-IPN active layer exhibited better hydrophilicity, higher negative zeta potential and surface roughness in comparison with NF membranes having virgin polypiperazinetrimesamide as the active layer. Semi-IPN membranes exhibited pure water permeability 103 ± 10 LMH at 150 psi pressure and rejection ratio of bivalent to monovalent salts as 2.7, whereas for virgin polypiperazinetrimesamide membrane the values, are 42 ± 5 LMH and 2.1, respectively. The semi-IPN NF membranes showed better antifouling behavior than the virgin polypiperazinetrimesamide membrane. The flux recovery ratio and total fouling ratio of semi-IPN NF membrane were observed 97.8 and 3.3% whereas for polypiperazinetrimesamide NF membranes, the values are 90.9 and 10.5%, respectively.     

聚四氟乙烯膜及应用1998-2017文献计量分析

对汤森路透科学网络数据库(WOS)核心合集中,关于聚四氟乙烯(PTFE)膜的出版物进行文献计量概述。根据1998-2017年核心合集的2 555篇论文,从基本增长趋势分析、关键词分析、突发检测等方面展开研究。结果表明,PTFE膜研究最具生产力的国家为中国、美国和日本,且世界各国、机构和研究者之间的合作日益频繁。通过关键词识别出4个聚类,表明PTFE膜研究的主要方向包括膜改性、膜分离、在能源电池和口腔医学中的应用。PTFE膜在膜燃料电池气体扩散层和膜蒸馏方面的应用研究成为近年的研究热点。     

Surface-tailoring chlorine resistant materials and strategies for polyamide thin film composite reverse osmosis membranes

Polyamide thin film composite membranes have dominated current reverse osmosis market on account of their excellent separation performances compared to the integrally skinned counterparts. Despite their very promising separation performance, chlorine-induced degradation resulted from the susceptibility of polyamide toward chlorine attack has been regarded as the Achilles’s heel of polyamide thin film composite. The free chlorine species present during chlorine treatment can impair membrane performance through chlorination and depolymerization of the polyamide selective layer. From material point of view, a chemically stable membrane is crucial for the sustainable application of membrane separation process as it warrants a longer membrane lifespan and reduces the cost involved in membrane replacement. Various strategies, particularly those involved membrane material optimization and surface modifications, have been established to address this issue. This review discusses membrane degradation by free chlorine attack and its correlation with the surface chemistry of polyamide. The advancement in the development of chlorine resistant polyamide thin film composite membranes is reviewed based on the state-of-the-art surface modifications and tailoring approaches which include the in situ and post-fabrication membrane modifications using a broad range of functional materials. The challenges and future directions in this field are also highlighted.