Proton Conductivity and Free Volume Properties in Per-Fluorinated Sulfonic acid/PTFE Copolymer for Fuel Cell (original) (raw)
Related papers
Journal of Power Sources, 2007
In the present study, we examine the water and proton transport properties of hexafluorinated sulfonated poly(arylenethioethersulfone) (6F-SPTES) copolymer membranes for applications to proton exchange membrane fuel cells (PEMFCs). The 6F-SPTES copolymer membranes build upon the structures of previously studied sulfonated poly(arylenethioethersulfone) (SPTES) copolymer membranes to include CF 3 functional groups in efforts to strengthen water retention and extend membrane performance at elevated temperatures (above 120 • C). The 6F-SPTES copolymer membranes sustain higher water self-diffusion and greater proton conductivities than the commercial Nafion ® membrane. Water diffusion studies of the 6F-SPTES copolymer membranes using the pulsed-field gradient spin-echo NMR technique reveal, however, the fluorinated membranes to be somewhat unfavorable over their non-fluorinated counterparts as high temperature membranes. In addition, proton conductivity measurements of the fluorinated membranes up to 85 • C show comparable results with the non-fluorinated SPTES membranes.
Highly fluorinated comb-shaped copolymer as proton exchange membranes (PEMs): Fuel cell performance
Journal of Power Sources, 2008
The fuel cell performance (DMFC and H 2 /air) of highly fluorinated comb-shaped copolymer is reported. The initial performance of membrane electrode assemblies (MEAs) fabricated from comb-shaped copolymer containing a side-chain weight fraction of 22% are compared with those derived from Nafion and sulfonated polysulfone (BPSH-35) under DMFC conditions. The low water uptake of comb copolymer enabled an increase in proton exchange site concentrations in the hydrated polymer, which is a desirable membrane property for DMFC application. The comb-shaped copolymer architecture induces phase separated morphology between the hydrophobic fluoroaromatic backbone and the polysulfonic acid side chains. The initial performance of the MEAs using BPSH-35 and Comb 22 copolymer were comparable and higher than that of the Nafion MEA at all methanol concentrations. For example, the power density of the MEA using Comb 22 copolymer at 350 mA cm −2 and 0.5 M methanol was 145 mW cm −2 , whereas the power densities of MEAs using BPSH-35 were 136 mW cm −2 . The power density of the MEA using Comb 22 copolymer at 350 mA cm −2 and 2.0 M methanol was 144.5 mW cm −2 , whereas the power densities of MEAs using BPSH-35 were 143 mW cm −2 .
Copyright © 2017 John Wiley & Sons, Ltd., 2017
The possibility of developing low-cost commercial grafted and sulfonated Poly(vinylidene fluoride) (PVDF-g-PSSA) membranes as proton exchange membranes for fuel cell applications have been investigated. PVDF-g-PSSA membranes were systematically prepared and examined with the focus of understanding how the polymer microstructure (degree of grafting and sulfona-tion, ion-exchange capacity, etc) affects their methanol permeability, water uptake, and proton conductivity. Fourier transform infrared spectroscopy was used to characterize the changes of the membrane's microstructure after grafting and sulfonation. The results showed that the PVDF-g-PSSA membranes exhibited good thermal stability and lower methanol permeability. The proton conductivity of PVDF-g-PSSA membranes was also measured by the electrochemical impedance spectroscopy method. It was found that the proton conductivity of PVDF-g-PSSA membranes depends on the degree of sulfonation. All the sulfonated membranes show high proton conductivity at 92°C, in the range of 27 to 235 mScm −1 , which is much higher than that of Nafion212 (102 mScm −1 at 80°C). The results indicated that the PVDF-g-PSSA membranes are particularly promising membranes to be used as polymer electrolyte membranes due to their excellent stability, low methanol permeability, and high proton conductivity. KEYWORDS Poly(vinylidene flouride), degree of sulfonation, water uptake, Ion exchange capacity, proton conductivity, methanol Permeability 1 | INTRODUCTION Recently, ion-conducting membranes are regarded as important materials because of the various fields in which they can be applied: ion exchangers, in water treatment, rechargeable batteries, electrochromic devices, and in electrolysis. 1,2 One important application for this kind of membranes is the proton-exchange membrane fuel cell (PEMFC) that is a promising power source for low-emission vehicles. The PEMFC is the most suitable type of fuel cells for terrestrial vehicles owing to its low operation temperature, high energy efficiencies and high power densities. The PEMFC has interested considerable research in chemistry, physics, and theory. 3-7 The proton-exchange membrane (PEM) is a key component in PEMFC, which serves as both an electrolyte and separa-tor. Because of the requirements of the environment, an ideal PEM material requires a combination of chemical and physical properties: long-term chemical and electrochemical stability in the reducing environment at the cathode and the harsh oxidative environment at the anode, good mechanical strength, and dimensional stability in tight PEM stacks, and high proton conductivity under various operational conditions (ie, temperatures and relative humidity). A lot of polymers have been prepared and studied in the past decades with some successes and limitations. These polymers are mainly known as fluoropolymers 8-10 and aromatic hydrocarbon polymers. 11-13 The most commonly known polymer is Nafion (sulfonated fluoropolymer), which has high stability and good proton conductivity in low temperatures and high relative-humidity conditions. However, the Nafion-based PEM is expensive, and its conductivity showed reduction at higher temperatures (>80°C) and low humidity (<40%) conditions. A lot of studies have been performed with the goal of developing alternative membranes , focusing on the reduction of the methanol permeability. Some of them have worked on developing new synthetic polymeric membranes that have ionic clusters, 14-17 or the modification of the Nafion membranes by surface treatment or by blending them with other
Journal of Membrane Science, 2010
The effect of side chain architectures on the properties and proton conductivities of graft copolymer membranes for direct methanol fuel cells (DMFCs) are studied. Poly(vinylidene fluoride)-g-poly(styrene sulfonic acid) (PVDF-g-PSSA) copolymers with either linear or arborescent PSSA side chains are prepared and examined. For the copolymers with similar ion exchange values, both graft copolymers show similar water uptakes and bound water contents. Meanwhile, the arborescent samples exhibit higher proton conductivity, lower methanol permeability, and higher selectivity compared to the linear analogues. Incorporation of highly branched side chains effectively increases the properties of the PVDF-g-PSSAbased PEMs for DMFCs because of formation of agglomerate PSSA domains. The PSSA domains promote proton conduction and depress methanol permeation through the PEMs, consequently significantly increase the selectivities (proton conductivity/methanol permeability) of the PEMs.
Journal of Polymer Research, 2015
A versatile and diverse grafting method was employed in the preparation of perfluorinated PEMs, in which poly(vinyl phosphonic acid) (PVPA) and poly(vinylidene fluoride) (PVDF) were chemically combined by means of poly(glycidyl methacrylate) (PGMA) grafts. Alkaline treated PVDF was used as a macromolecule in conjunction with GMA in the graft copolymerization. Various PVDF-g-PGMA-g-PVPA membranes were obtained upon simply mixing PVDF-g-PGMA and PVPA at several ratios by mass. The composition and the structure of the membranes were characterized by Energy Dispersive X-ray spectroscopy (EDS), 1 H-NMR, 19 F-NMR, and FTIR. Thermogravimetric analysis (TGA) demonstrated that the PVDF-g-PGMA and PVDF-g-PGMA-g-PVPA membranes were thermally stable up to 275 and 210°C, respectively. The surface roughness and morphology of the membranes were studied using Atomic Force Microscopy (AFM), X-ray diffraction (XRD) and Scanning Electron Microscopy (SEM). The proton conductivity increased with increasing temperature and PVPA ratio in the absence of humidity. The maximum proton conductivity in anhydrous conditions at 150°C was 0.0023 Scm −1 while in humidified conditions (under 50 % of RH) at 100°C a value of 0.034 Scm −1 was found.
2016
The polymer electrolyte membrane (PEM) electrolysis provides a sustainable solution for production of hydrogen with high purity. The most commonly used PEM, the perfluorosulfonic acid membrane (Nafion), successfully works at temperatures up to 80C, however above 90-100 C Nafion it loses both conductivity and mechanical stability. Therefore, there is a need for development of PEM with different chemical structure capable to resist elevated temperatures. This work presents a comparative study on the properties of two commercial and three laboratory prepared PBI membranes applicable for preparation of membrane electrode assemblies for high temperature PEM water electrolysis. The proton conductivity is measured at temperatures up to 170 C applying the method of impedance spectroscopy. It is found that the conductivity decreases in the order Celtec®-P >p-PBI>m-PBI≥ABPBI. The differences are discussed in connection with the polymer structure and type of proton transfer mechanism...
A novel PTFE-based proton-conductive membrane
Journal of Power Sources, 2006
The demand for a solid polymer electrolyte membrane (SPEM) for fuel-cell systems, capable of withstanding temperatures above 130 • C, decreasing the electrode-catalyst loadings and reducing poisoning by carbon monoxide, has prompted this study. A novel, low-cost, highly conductive, nanoporous proton-conducting membrane (NP-PCM) based on a polytetrafluoroethylene (PTFE) backbone has been developed. It comprises non-conductive nano-size ceramic powder, PTFE binder and an aqueous acid. The preparation procedures were studied and the membrane was characterized with the use of: SEM, EDS, pore-size-distribution measurements (PSD), TGA-DTA and electrochemical methods. The ionic conductivity of a membrane doped with 3 M sulfuric acid increases with the ceramic powder content and reaches 0.22 S cm −1 at 50% (v/v) silica. A non-optimized direct-methanol fuel cell (DMFC) with a 250 m thick membrane has been assembled. It demonstrated 50 and 130 mW cm −2 at 80 and 130 • C, respectively. Future study will be directed to improving the membrane-preparation process, getting thinner membranes and using this membrane in a hydrogen-fed fuel cell.
Journal of Power Sources, 2007
Fluorinated polymers are today investigated as possible alternatives to Nafion TM in PEM Fuel Cells. In this paper, we study the relationships between the microstructure and the proton transport of porous PVDF homopolymer membranes swollen by 11 M aqueous solution of H 3 PO 4 . The analysis is performed on membranes with different nominal pores size values, d p . The membranes are thermally stable at least up to 250 • C. A dependence of the proton transport on the pores size has been found, that is particularly evident for low d p values and at low relative humidity (R.H.). Conductivity values exceeding 0.1 S cm −1 are obtained at 80 • C even at 10% R.H. for d p ≥ 0.22 m. We show that the behaviour of the transport properties cannot be simply rationalized in terms of d p , but it requires an accurate knowledge of the membrane microstructure (tortuosity, pores interconnections and size distributions). 31 P NMR spectroscopy also shows that anisotropic interactions take place between the components of the solution and at a lower extent, between the solution and the pores walls, also for d p values in the micrometer range. In order to make a preliminary check of the suitability of these membranes for applications in Direct Methanol Fuel Cells (DMFCs), studies of methanol crossover and diffusion through the membrane have been carried out and compared with those of Nafion TM .
International Journal of Hydrogen Energy, 2014
We report on polymer electrolyte membrane fuel cells (PEMFCs) that function at high temperature and low humidity conditions based on short-side-chain perfluorosulfonic acid ionomer (SSC-PFSA). The PEMFCs fabricated with both SSC-PFSA membrane and ionomer exhibit higher performances than those with long-side-chain (LSC) PFSA at temperatures higher than 100 C. The SSC-PFSA cell delivers 2.43 times higher current density (0.524 A cm À1) at a potential of 0.6 V than LSC-PFSA cell at 140 C and 20% relative humidity (RH). Such a higher performance at the elevated temperature is confirmed from the better membrane properties that are effective for an operation of high temperature fuel cell. From the characterization technique of TGA, XRD, FT-IR, water uptake and tensile test, we found that the SSC-PFSA membrane shows thermal stability by higher crystallinity, and chemical/mechanical stability than the LSC-PFSA membrane at high temperature. These fine properties are found to be the factor for applying Aquivion™ E87-05S membrane rather than Nafion ® 212 membrane for a high temperature fuel cell.
Membranes
Series of partially fluorinated sulfonated poly(arylene ether)s were synthesized through nucleophilic substitution polycondensation from three types of diols and superhydrophobic tetra-trifluoromethyl-substituted difluoro monomers with postsulfonation to obtain densely sulfonated ionomers. The membranes had similar ion exchange capacities of 2.92 ± 0.20 mmol g−1 and favorable mechanical properties (Young’s moduli of 1.60–1.83 GPa). The membranes exhibited considerable dimensional stability (43.1–122.3% change in area and 42.1–61.5% change in thickness at 80 °C) and oxidative stability (~55.5%). The proton conductivity of the membranes, higher (174.3–301.8 mS cm−1) than that of Nafion 211 (123.8 mS cm−1), was the percent conducting volume corresponding to the water uptake. The membranes were observed to comprise isolated to tailed ionic clusters of size 15–45 nm and 3–8 nm, respectively, in transmission electron microscopy images. A fuel cell containing one such material exhibited hi...