1,721,041 research outputs found
ETFE-g-pentafluorostyrene: functionalization and proton conductivity
No full textIn this study we propose a relatively simple and versatile method for the preparation of a polyelectrolyte membrane based on poly(pentafluorostyrene) (PFS) owing proton exchange functionalities for proton conducting applications. The method includes two steps: grafting of the PFS from an irradiated ETFE film, followed by post-functionalization. The advantage of our approach lies in grafting a polymer with highly reactive functional groups suitable for efficient post-sulfonation/phosphonation. The grafting step is optimized both in terms of the system (bulk, non-/solvent and gas-phase grafting) and the conditions (radiation doses, time and temperature) used. The kinetics of the grafting shows a linear increase of grafting degree with both time and temperature suggesting a lower diffusion control and a reduced termination reaction rate for the optimized grafting process. Both phosphonation and sulfonation of the PFS grafted ETFE result in a corresponding high functionalization degree of 50% and 70% with IEC values of 1 and 1.5 mequiv g−1 and conductivities of 170 and 90 mS cm−1 at 120 °C, 90% RH for the sulfonated and phosphonated ETFE-g-PFS respectively. The high conductivity is attributed to the homogeneous distribution of the PFS within the ETFE matrix (EDX-SEM micrographs) and relatively high acidities of the sulfonic and the phosphonic acid
Cross-linked PBI-based high-temperature membranes: stability, conductivity and fuel cell performance
No full textIn this study different types of polybenzimidazole(PBI)-based High-T fuel cell membranes were investigated comparatively. The different membranes comprised: (1) ionically cross-linked PBI-excess blend membranes by mixing PBI (the polybenzimidazoles PBIOO and F6PBI) with different cation-exchange ionomers such as poly(tetrafluorostyrene-4-phosphonic acid), and different nonfluorinated and partially fluorinated sulfonated arylene main-chain polymers, where the cation-exchange groups form ionical cross-links with the imidazole groups of the PBI by proton transfer; (2) covalently cross-linked PBI-excess membranes by mixing PBI with different halomethylated arylene polymers where the halomethyl groups form covalent cross-links towards the imidazole group of the PBI by alkylation of the N–H group: polymer-CH2Br + PBI-imidazole-N-H → polymer–CH2–N-imidazole-PBI; (3) PBI-anion-exchange polymer blends; (4) covalent-ionically cross-linked PBI blend membranes by mixing PBI with a sulfonated polymer and a halomethylated polymer. The membranes were investigated in terms of: (i) chemical stability by Fentons Test (FT), (ii) extent of cross-linking by extraction with DMAc, (iii) thermal stability by TGA, (iv) H+-conductivity in the T range 80–150 °C as H3PO4-doped membranes, and (v) fuel cell performance in a high-T H2/air fuel cell. The general results of the study were summarized as follows: (1) Most of the membranes showed excellent chemical stability in FT; (2) the PBI blends with F6PBI showed better chemical stabilities than the PBIOO-containing blends; (3) the proton conductivities of all investigated membranes were in a range of 4–90 mS/cm at T from 80 to 150 °C; (4) the fuel cell test results of the membranes were promisin
Sulfonated poly(pentafluorostyrene): synthesis & characterization
No full textPreparation of a high molecular weight polypentafluorostyrene (PFS) and sulfonated polypentafluorostyrene
(sPFS) is described in this paper. The high molecular weight PFS was obtained via classical emulsion polymerization
reaction, which increased the molecular weight of PFS of about one order of magnitude higher than the
one of the commercial polymer. The molecular weight is a crucial factor for the film forming properties of a
polymer membrane, following the concept the higher–the better. Furthermore, we post-sulfonated the PFS
by 100% (one sulfonic acid per styrene unit). This provided a polymer possessing very high ion-exchange
capacity (IEC = 3.4 mmol g−1) with functional group coupled to the relatively flexible side units (phenyl
rings). The phenyl rings are fluorinated which enhanced the nucleophilic substitution reaction (introduction
of the functional groups) and reduced the pKa value of the resulting sulfonic acid (pKa = −2). The morphology
of sPFS, studied by Small Angle Neutron and X-rays Scattering, revealed a high ordering of a nano-phaseseparated
system. All these factors raised the conductivity to one of the highest measured on polyelectrolyte
(σ = 36 mS cm−1 at T = 160 °C, p(H2O) = 105 Pa). This value is one order of magnitude higher than the
conductivity of Nafion 117 measured under the same condition
Development and testing of an anion exchange membrane electrolyser
No full textIn the context of energy policy and the use of renewable energies, our research institute collaborates with other partners on the development of a compact, environmental-friendly and effective electrolyser for efficient power storage. This electrolyser combines the positive properties of the alkaline water electrolysis and the proton exchange membrane (PEM) electrolysis. On the cathode side on porous current collectors were electrodeposited in one step multi-component non-precious alloys. New cross-linked anion-exchange membranes have been developed to achieve high ionic conductivity. The anode side was coated with the sol–gel method. The catalytic activity of the electrodes was investigated by electrochemical studies. Current collectors have been tested under real conditions of electrolysis. For the construction of a corresponding single cell, media supply was taken into consideration and appropriate materials for current collectors, the bipolar plates and gaskets were selecte
High performance anode based on a partially fluorinated sulfonated polyether for direct methanol fuel cells operating at 130 °C
No full textDue to the disadvantages of the Nafion polymer for the application in the direct methanol fuel cell (DMFC) especial at temperatures above 100 °C several polymers of the hydrocarbon type have already been investigated as membranes and ionomers in the DMFC. Among them were nonfluorinated and partially fluorinated arylene main-chain hydrocarbon polymers. In previous work, sulfonated polysulfone (sPSU) has been applied as the proton-conductive binder in the anode of a DMFC, ending up in good and stable performance. In continuation of this work, in the study presented here a polymer was prepared by polycondensation of decafluorobiphenyl and bisphenol AF. The formed polymer was sulfonated after polycondensation by oleum and the obtained partially fluorinated sulfonated polyether (SFS) was used as the binder and proton conductor in a DMFC anode operating at a temperature of 130 °C. The SFS based anode with 5% as ionomer showed comparable performance for the methanol oxidation to Nafion based anodes and significant reduced performance degradation versus Nafion and sPSU based anodes on the Nafion 115 membrane. Membrane electrode assemblies (MEAs) with the SFS based anode showed drastically improved performance compared to MEAs with Nafion based anodes during operation with lower air pressure at the cathodeAiF and Grant no IGF-16593BG/
Synthesis and characterization of fluorinated and sulfonated poly(arylene ether-1,3,4-oxadiazole) derivatives and their blend membranes
No full textSupplementary data associated with this article can be
found, in the online version, at http://dx.doi.org/10.1016/
j.eurpolymj.2013.12.003In this study we present the synthesis and characterization of sulfonated poly(arylene
ether-1,3,4-oxadiazole) derivatives. The polymers were prepared by the polycondensation
reaction of bisphenol A, bisphenol S and bisphenol AF with 2,5-bis(pentafluorophenyl)-
1,3,4-oxadiazole, followed by sulfonation with oleum. The polymers were characterized
using elemental analysis, 1H, 13C and 19F NMR analysis. The obtained polyelectrolytes were
blended with excess of polybenzimidazoles producing stable and flexible polymer films
which showed high thermal stability and reasonable proton conductivity after doping with
phosphoric acid. This study confirms that poly(arylene ether 1,3,4-oxadiazole)s are promising
candidates as proton exchange membranes in intermediate- and high-temperature
fuel cell applicationsFinanced in-part by a DFG
project entitled ‘‘Ion-exchange membranes for intermediate
T fuel Cells’’ with the reference number KE 673/10-
Highly phosphonated polypentafluorostyrene blended with polybenzimidazole: application in vanadium redox flow battery
No full textThis study discusses the synthesis and preparation of ionically cross-linked acid-base blend membranes based on phosphonated poly(pentafluorostyrene) and poly(benzimidazole) for vanadium redox flow battery application (VRFB). Poly(pentafluorostyrene) was obtained by emulsion polymerization and reacted with tris(trimethylsilyphosphite) to obtain highly phosphonated poly(pentafluorostyrene) (PWN). For obtaining chemically and mechanically stable membrane PWN was blended with poly(benzimidazole) (F6PBI) in different weight ratios. The blend membranes showed high resistance to heat (above 400 °C) and the harsh conditions of the VRFB (highly acid and oxidizing conditions). Among the blends, the membrane consisting of PWN/F6PBI (9/1) weight ratio was identified as the most suitable separator due to its high ion-exchange capacity and conductivity. Additionally, this membrane showed the highest Coulomb efficiency (99%) proving its excellent separation ability for VRFB electrolytes. A more detailed study of this blend membrane revealed low self-discharge rate of about 1.6 mV h−1 being almost an order of magnitude lower than those of Nafion®212 (10.7 mV h−1) and lasting above 120 h to the voltage drop. Additionally, the membrane showed no lost of capacity until 600 charge-discharge cycles and only 30% after the 1600 cycles. Thus, in this study, we were able to show for the first time the potentials of a phosphonic acid based electrolyte separator for the application in VRF
Highly phosphonated polypentafluorostyrene: characterization and blends with polybenzimidazole
No full textIn this study we present results of the conductivity and resistance to thermooxidative and
condensation reactions of a highly phosphonated poly(pentafluorostyrene) (PWN2010)
and of its blends with poly(benzimidazole)s (PBI). This polymer, which combines both:
(i) a high degree of phosphonation (above 90%) and (ii) a relatively high acidity (pKa (–PO3-
H2M–PO3H ) 0.5) due to the fluorine neighbors, is designed for low humidity operating
fuel cell. This was confirmed by the conductivity measurements for PWN2010 reaching
r = 5 10 4 S cm 1 at 150 C in dry N2 and r = 1 10 3 S cm 1 at 150 C (k = 0.75). Furthermore,
this polymer showed only 48% of anhydride formation when annealing it at
T = 250 C for 5 h and only 2% weight loss during a 96 h Fenton test. These properties combined
with the ability of the PWN2010 to form homogeneous blends with polybenzimidazoles
resulting in stable and flexible polymer films, makes PWN2010 a very promising
candidate as a polymer electrolyte for intermediate- and high-temperature fuel cell
applications
Simple fabrication of 12 μm thin nanocomposite fuel cell membranes by direct electrospinning and printing
No full textDirect membrane deposition (DMD) was recently introduced as a novel polymer electrolyte membrane fabrication method. Here, this approach is extended to fabricate 12 μm thin nanocomposite fuel cell membranes. Poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) nanofibers are directly electrospun onto gas diffusion electrodes. By inkjet-printing Nafion ionomer dispersion into the pore space of PVDF-HFP nanofiber mats, composite membranes of 12 μm thickness were fabricated. At 120 °C and 35% relative humidity, stoichiometric 1.5/2.5 H2/air flow and atmospheric pressure, the power density of the DMD fuel cell (0.19 W cm-2), was about 1.7 times higher than that of the reference fuel cell (0.11 W cm-2) with Nafion HP membrane and identical catalyst. A lower ionic resistance and, especially at 120 °C, a reduced charge transfer resistance is found compared to the Nafion HP membrane. A 100 h accelerated stress test revealed a voltage decay of below 0.8 mV h-1, which is in the range of literature values for significantly thicker reinforced membranes. Finally, this novel fabrication approach enables new degrees of freedom in the design of complex composite membranes. The presented combination of scalable deposition techniques has the potential to simplify and thus reduce cost of composite membrane fabrication at a larger scal
Perfluoro-p-xylene as a new unique monomer for highly stable arylene main-chain ionomers applicable to low-t and high-t fuel cell membranes
Get PDFIn this study, we present the synthesis and the characterization of novel functionalized arylene main-chain ionomers based on perfluoro-p-xylene (PFX). The polymers were prepared by polycondensation of PFX and 4,4'-dihydroxybiphenyl or bisphenol 2,2-bis(4-hydroxyphenyl)-hexafluoropropane (bisphenol AF). After polymerization, the PFX unit was still able to undergo nucleophilic aromatic substitution reaction, which was used to introduce phosphonic acid groups into the polymer via a reaction with tris(trimethylsilyl)phosphite. Furthermore, electrophilic sulfonation of these polymers was possible in the bisphenol unit when using H2SO4/SO3 as the sulfonation agent. The so-obtained water-soluble PFX-based polyelectrolytes showed excellent chemical stability and were blended with polybenzimidazoles. The blend membranes formed flexible and mechanically robust films with excellent chemical and thermal stabilitie
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