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.     

Cell performances of direct methanol fuel cells with grafted membranes

Cell performances were evaluated with grafted polymer membranes as an electrolyte for a direct methanol fuel cell (DMFC). The membranes were prepared using a poly(ethylene-tetrafluoroethylene), or ETFE, film. The base polymer film was added to sulfonic groups using γ-radiation activated grafting technique as ion-exchange groups. These membranes had more suitable properties for DMFCs, i.e. higher electric conductivity and lower methanol permeability than perfluorinated ionomer membrane (Nafion). Nevertheless, the cell performance with the grafted membrane was inferior to that with Nafion. The analysis of electrode potentials vs. reversible hydrogen electrode showed larger activation overpotential for both the electrodes on the grafted membranes. We concluded that this is due to poor bonding of the catalyst layers to the grafted membranes.     

Effect of operating conditions on energy efficiency for a small passive direct methanol fuel cell

Energy conversion efficiency was studied in a direct methanol fuel cell (DMFC) with an air-breathing cathode using Nafion 117 as electrolyte membrane. The effect of operating conditions, such as methanol concentration, discharge voltage and temperature, on Faradic and energy conversion efficiencies was analyzed under constant voltage discharge with quantitative amount of fuel. Both of Faradic and energy conversion efficiencies decrease significantly with increasing methanol concentration and environmental temperature. The Faradic conversion efficiency can be as high as 94.8%, and the energy conversion efficiency can be as high as 23.9% if the environmental temperature is low enough (10 °C) under constant voltage discharge at 0.6 V with 3 M methanol for a DMFC bi-cell. Although higher temperature and higher methanol concentration can achieve higher discharge power, it will result in considerable losses of Faradic and energy conversion efficiencies for using Nafion electrolyte membrane. Development of alternative highly conductive membranes with significantly lower methanol crossover is necessary to avoid loss of Faradic conversion efficiency with temperature and with fuel concentration.     

氧化石墨烯在燃料电池质子交换膜中的应用

保护环境，开发环保型能源，对人类和社会具有重要意义。质子交换膜燃料电池由于其能量转化率高，可实现零排放，近年来引起了电池领域研究者们的兴趣。氧化石墨烯（GO）由于存在活性氧官能团，可以和离子型聚合物进行复合以制备复合质子交换膜。氧化石墨烯类的复合质子交换膜应用于燃料电池时可以提高膜在高温低湿度条件下的质子传导率，降低甲醇渗透率，提高电池的功率密度。本文首先介绍了氧化石墨烯的制备方法，然后从不同的离子型聚合物基质复合质子交换膜的类别出发，详细介绍了氧化石墨烯在Nafion、聚醚醚酮、聚苯并咪唑和壳聚糖等不同种类的离子型聚合物中的应用现状及作用机理，同时对其在质子交换膜的应用方面存在的问题及应用前景做了评论和展望。     

再铸全氟磺酸-聚四氟乙烯共聚物/磺化氧化锆复合膜的制备与性能研究

利用溶液再铸法制备了全氟磺酸－聚四氟乙烯共聚物 （Nafion?）/磺化氧化锆（SZ）复合膜,借助X射线衍射、扫描电子显微镜、热失重分析仪等研究了所制备复合膜的微观结构、形貌以及性能。结果表明,棒状SZ颗粒以平行于膜表面的方向排列,均匀分布在Nafion?膜的骨架中,改善了膜在中温区的热稳定性;将复合膜用于直接甲醇燃料电池（DMFC）的电解质膜时,使用了3 ％ 和6 ％SZ的Nafion?/SZ复合膜的DMFC在45 ℃和5 mol/L甲醇进料时的峰值输出功率密度分别为46.27、59.47 mW/cm2,明显高于同样条件下Nafion?膜的38.2 mW/cm2。     

Improvement of the Nafion–polytetrafluoroethylene membranes for potential direct methanol fuel cell use by reduction of the methanol crossover

The possibility of ultrathin Nafion/expanded polytetrafluoroethylene (ePTFE) membranes used as proton‐exchange membranes (PEMs) for direct methanol fuel cells (DMFCs) was investigated in this study. Nafion/ePTFE membranes with a thickness of ～ 14 μm were promoted by self‐assembling Pd nanoparticles on the surface to reduce the methanol crossover. The loading of the Pd nanoparticles assembled on the membranes was 1.6–1.8 μg/cm² and had little effect on the high conductivity of the Nafion membranes. With the self‐assembly of Pd nanoparticles, the methanol permeation noticeably decreased from 340 to 28 mA/cm². As a result, the open‐ circuit voltage of the Nafion/ePTFE membranes that were self‐assembled for 48 h had a more significant increase from 0.55 to 0.73 V. The reduction of methanol crossover significantly increased the DMFC voltage‐current performance, and this means that self‐assembled Nafion/polytetrafluoroethylene PEMs have promise in DMFCs. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

直接甲醇燃料电池溶胶-凝胶流动相的制备与表征

对直接甲醇燃料电池溶胶-凝胶流动相的制备工艺进行了分析,采用溶胶-凝胶法以正硅酸甲酯为前驱体制备出了溶胶-凝胶流动相.分别以溶胶-凝胶流动相和液体流动相为燃料对比研究了直接甲醇燃料电池的放电性能,测定了溶胶-凝胶流动相在Nation117膜中的甲醇渗透率,研究了溶胶-凝胶流动相的质子电导率.实验结果表明,使用溶胶-凝胶...     

AC‐Impedance Investigation of Different MEA Configurations for Passive‐Mode DMFC Mini‐Stack Applications

Membrane‐electrode assemblies (MEAs) characterised by different hydrophobic–hydrophilic properties were investigated in a passive Direct methanol fuel cell (DMFC) monopolar mini‐stack at room temperature. These properties were modulated by varying the amount of Nafion or replacing the ionomer in the catalytic layer with polytetrafluoroethylene (PTFE). Impedance spectroscopy provided valuable information with respect to the limiting processes occurring during fuel cell operation. Methanol crossover, especially in the presence of high methanol concentration, played a major role in determining the overall performance. The development of a methanol impermeable membrane appears crucial for increasing the performance of DMFC devices for portable applications.     

Characterization and fuel cell performance analysis of polyvinylalcohol–mordenite mixed-matrix membranes for direct methanol fuel cell use

Polyvinylalcohol–mordenite (PVA–MOR) mixed matrix membranes were synthesized for direct methanol fuel cell (DMFC) use. For the structural and the morphological characterization, Scanning Electron Microscopy and Thermal Gravimetric Analysis methods were used. Zeolite distribution within the polymer matrix was found to be homogeneous. An impedance spectroscope was used to measure the proton conductivity. In order to obtain information about methanol permeation characteristics, swelling tests and a series of pervaporation experiments were carried out. 60–40 wt% PVA–MOR membranes were found to give the optimum transport properties. Proton conductivity of these membranes was found to be slightly lower than that of Nafion117™ whereas their methanol permeability was at least two orders of magnitude lower than Nafion117™. DMFC performance of the PVA–MOR membranes was also measured. The inferior DMFC performance of PVA–MOR membranes was linked to drying in the fuel cell medium and the consequent proton conductivity loss. Their performance was improved by adding a dilute solution of sulfuric acid into the feed methanol solution. Future studies on the improvement of the proton conductivity of PVA–MOR membranes, especially via sulfonation of the polymer matrix, can overcome the low-performance problem associated with insufficient proton conductivity.     

Sulfonated poly(ether sulfone)/phosphotungstic acid/attapulgite composite membranes for direct methanol fuel cells

Novel composite sulfonated poly(ether sulfone)(SPES)/phosphotungstic acid (PWA)/attapulgite (AT) membranes were investigated for direct methanol fuel cells (DMFCs). Physical–chemical properties of the composite membranes were characterized by FTIR, DSC, TGA, SEM‐EDX, water uptake, tensile test, proton conductivity, and methanol permeability. Compared with a pure SPES membrane, PWA, and AT doping in the membrane led to a higher thermal stability and glass transition temperature (T_g) as revealed by TGA and DSC. Tensile test indicated that lower AT content (3%) in the composite can significantly increase the tensile strength, while higher AT loading demonstrated a smaller contribution on strength. Proper PWA and AT loadings in the composite membranes can increase the proton conductivity and lower the methanol cross‐over. The proton conductivity of the SPES‐P‐A 10% composite membrane reached 60% of the Nafion 112 membrane conductivity at room temperature while the methanol permeability was only one‐fourth of that of Nafion 112 membrane. This excellent performances of SPES/PWA/AT composite membranes could indicate a potential feasibility as a promising electrolyte for DMFC. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Nafion-TiO2 composite DMFC membranes: physico-chemical properties of the filler versus electrochemical performance

TiO₂ nanometric powders were prepared via a sol-gel procedure and calcined at various temperatures to obtain different surface and bulk properties. The calcined powders were used as fillers in composite Nafion membranes for application in high temperature direct methanol fuel cells (DMFCs). The powder physico-chemical properties were investigated by X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and pH measurements. The observed characteristics were correlated to the DMFC electrochemical behaviour. Analysis of the high temperature conductivity and DMFC performance reveals a significant influence of the surface characteristics of the ceramic oxide, such as oxygen functional groups and surface area, on the membrane electrochemical behaviour. A maximum DMFC power density of 350 mW cm⁻² was achieved under oxygen feed at 145 °C in a pressurized DMFC (2.5 bar, anode and cathode) equipped with TiO₂ nano-particles based composite membranes.     

Nafion-impregnated polyethylene-terephthalate film used as the electrolyte for direct methanol fuel cells

An electrolyte system for direct methanol fuel cells (DMFC) was prepared by basing its design on combination of the existing concepts such as a composite membrane and a barrier against methanol cross-over. A composite membrane was prepared by impregnating Nafion ionomer into 6 μm thick hydrophilic PETE (polyethylene-terephthalate) film whose average pore diameter was 0.3 μm. Owing to some features of the film such as high mechanical strength and less than 30% of its surface being occupied by the openings for proton passage, it was far more effective to block the passage with a very thin palladium film with the aim of preventing methanol cross-over. The DMFCs utilizing such a thin composite membrane as the electrolyte exhibited improved performances over those using conventional Nafion in the possibility of ambient temperature operation, higher current densities, and substantial reduction of methanol cross-over.     

Modified Sulfonated Poly(ether ether ketone) Based Mixed Matrix Membranes for Direct Methanol Fuel Cells

Mixed matrix membranes based on zeolite 4A‐methane sulfonic acid (MSA)‐sulfonated poly(ether ether ketone) (SPEEK) are evaluated as a potential polymer electrolyte membrane (PEM) for direct methanol fuel cells (DMFCs). Ion‐exchange capacity, sorption of water, and water–methanol mixture, proton conductivity, and methanol permeability for the mixed‐matrix membranes have been extensively investigated. The mixed‐matrix membranes are also characterized for their cross‐sectional morphology, mechanical, and thermal properties. DMFCs employing SPEEK‐MSA (20 wt.%) blend, zeolite 4A (4 wt.%)‐SPEEK‐MSA (20 wt.%) mixed matrix membranes deliver peak power densities of 130 and 159 mW cm^–2, respectively; while a peak power density of only 95 mW cm^–2 is obtained for the DMFC employing pristine SPEEK membrane at 70 °C. The results showed that these SPEEK based mixed matrix membranes exhibit higher DMFC performance and lower methanol permeability in comparison to Nafion‐117 membrane.     

PWA/silica doped sulfonated poly(ether sulfone) composite membranes for direct methanol fuel cells

A novel sulfonated poly(ether sulfone) (SPES)/phosphotungstic acid (PWA)/silica composite membranes for direct methanol fuel cells (DMFCs) application were prepared. The structure and performance of the obtained membranes were characterized by thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), scanning electron microscopy (SEM), water uptake, proton conductivity, and methanol permeability. Compared to a pure SPES membrane, PWA and SiO₂ doped membranes had a higher thermal stability and glass transition temperature (T_g) as revealed by TGA‐FTIR and DSC. The morphology of the composite membranes indicated that SiO₂ and PWA were uniformly distributed throughout the SPES matrix. Proper PWA and silica loadings in the composite membranes showed high proton conductivity and sufficient methanol permeability. The selectivity (the ratio of proton conductivity to methanol permeability) of the SPES‐P‐S 15% composite membrane was almost five times than that of Nafion 112 membrane. This excellent selectivity of SPES/PWA/silica composite membranes indicate a potential feasibility as a promising electrolyte for DMFC. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Modification of Nafion membranes with ternary composite materials for direct methanol fuel cells

Composite membranes for direct methanol fuel cells (DMFCs) were prepared by using Nafion115 membrane modification with polyvinyl alcohol (PVA), polyimide (PI) and 8-trimethoxysilylpropyl glycerin ether-1,3,6-pyrenetrisulfonic acid (TSPS). The performance of the composite membranes was evaluated in terms of water sorption, dimensional stability, thermal stability, proton conductivity, methanol permeability and cell performance. The proton conductivity was slightly decreased by 1-3% compared with Nafion115, which still kept the high proton conduction of Nafion115. The methanol permeability of Nafion/PI-PVA-TSPS composite membranes was remarkably reduced by 35-55% compared with Nafion115. The power density of DMFCs with Nafion/PI-PVA-TSPS composite membranes reached to 100 mW/cm², exceeding that with Nafion115 (68m W/cm²).     

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.     

Characterization and application of composite membranes in DMFC

The present work focuses on the characterization of membranes for direct methanol fuel cells (DMFC), prepared using composites of sulfonated poly(ether ether ketone) (sPEEK, with sulfonation degree, SD, of 42 and 68%) as polymer matrix. This polymer was inorganically modified incorporating different amounts of zirconium phosphate (ZrPh) pretreated with n-propylamine and polybenzimidazole (PBI). The investigated properties were: proton conductivity, water and aqueous methanol swelling, permeability coefficients for DMFC species and morphology. DMFC tests were performed at 110 °C with relative humidity (r.h.) in the cathode feed of 100 and 138%. The results obtained show that the inorganic modification of the polymer decreases the proton conductivity, water and aqueous methanol swelling and permeability towards DMFC species. In terms of morphology, it was found that the applied procedure enabled the preparation of membranes with good compatibility between inorganic and organic components. In terms of the DMFC tests of the composite membranes, working with the cathode feed at 100% r.h., the unmodified sPEEK membrane with SD = 42% proved to have the best performance, although with higher methanol crossover. In contrast, for r.h. of 138%, the best performance was achieved by the sPEEK composite membrane with SD = 68 and 20.0 wt.% of ZrPh and 11.2 wt.% of PBI.     

Optimization of operating parameters of a direct methanol fuel cell and physico-chemical investigation of catalyst–electrolyte interface

A physico-chemical investigation of catalyst–Nafion® electrolyte interface of a direct methanol fuel cell (DMFC), based on a Pt–Ru/C anode catalyst, was carried out by XRD, SEM-EDAX and TEM. No interaction between catalyst and electrolyte was detected and no significant interconnected network of Nafion micelles inside the composite catalyst layer was observed. The influence of some operating parameters on the performance of the DMFC was investigated. Optimal conditions were 2 M methanol, 5 atm cathode pressure and 2–3 atm anode pressure. Power densities of 110 and 160 mW cm⁻² were obtained for operation with air and oxygen, respectively, at temperatures of 95–100°C and with 1 mg cm⁻² Pt loading.     

直接甲醇燃料电池技术及应用

本文回顾了直接甲醇燃料电池（ＤＭＦＣ）的研究开发历史,系统阐述了ＤＭＦＣ系统中电催化剂选择与设计基本原则、电解质膜材料与甲醇渗透的关系。分析了电池工作温度、工作压力和甲醇进料方式对ＤＭＦＣ电化学性能的影响。     

Functionalization of polymeric materials as a high performance membrane for direct methanol fuel cell: A review

A coherent review on the advanced proton exchange membranes (PEMs) for direct methanol fuel cell (DMFC) application and the future direction in the development of a high performance polymeric membrane for DMFC were discussed in this paper. PEMs have a profound influence on performance of DMFC. The PEMs are categorized into five groups which are partially fluorinated, perfluorinated ionomers, acid–base complexes, non-fluorinated ionomers, hydro carbon and aromatic polymers. Many researchers have investigated the functionalization methods on the PEMs to solve methanol crossover problem while obtaining low electronic conductivity, high proton conductivity, low electro osmotic drag coefficient, high mechanical properties and good chemical and thermal stability. Including in this review, fabrication of PEM using electrospinning process coupled with the promising functionalized polymeric materials which were known to be the most important initiatives at present in order to further expand the full potential of DMFC performance.