High Performance Perfluoropolymer Films and Membranes

Arcella, V.; Ghielmi, Alessandro; Tommasi, Giulio

doi:10.1111/j.1749-6632.2003.tb06002.x

Cited by 174 publications

(120 citation statements)

References 12 publications

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“…7a and b, respectively. The n = 4 fragment is hypothetical, as with the current synthesis method 9 an even number of CF 2 groups separating the side chains is not possible, but when n r 4 the side chains have sufficient conformational freedom to enable their association through two hydrogen bonds. However, for n Z 5, the energy required for distortion of the side chains, or rotation about the carbon bonds in the main chain, appears to be too great to allow the sulfonic acid groups to hydrogen bond with one another in the absence of water.…”

Section: Quantum Chemical Calculationsmentioning

confidence: 99%

Modelling of morphology and proton transport in PFSA membranes

Elliott

Paddison

2007

Phys. Chem. Chem. Phys.

227

255

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Computational modelling studies of the structure of perfluorosulfonic acid (PFSA) ionomer membranes consistently exhibit a nanoscopic phase-separated morphology in which the ionic side chains and aqueous counterions segregate from the fluorocarbon backbone to form clusters or channels. Although these investigations do not unambiguously predict the size or shape of the clusters, and whether or not the channels percolate the matrix or if the connections between them are more transient, the sequence of co-monomers along the main chain appears strongly to influence the domain size of the ionic regions, with more blocky sequences giving rise to larger domain sizes. The fundamental insight that substantial rearrangement of the sulfonic acid terminated side chains and fluorocarbon backbone takes place during swelling or shrinkage is borne out by both molecular and mesoscale simulations of model PFSA polymers, along with ab initio electronic structure calculations of minimally hydrated oligomeric fragments. Molecularlevel modelling of proton transport in PFSA membranes attests to the complexity of the underlying mechanisms and the need to examine the chemical and physical processes at several distinct time and length scales. These investigations have revealed that the conformation of the fluorocarbon backbone, flexibility of the sidechains, and degree of aggregation and association of the sulfonic acid groups under minimally hydrated conditions collectively control the dissociation of the protons and the formation of Zundel and Eigen cations. The former appear to be the dominant charge carriers when the limiting water content allows only for the formation of a contact ion pair with the tethered sulfonate anion. As the water content increases, solventseparated Eigen ions begin to appear, indicating that the dominant mechanism for diffusion of protons occurs over a region approximately 4 Å away from the sulfonate groups. Finally, both the vehicular and Grotthuss shuttling mechanisms contribute to the mobility of the protons but, surprisingly, they are not always correlated, resulting in a lower overall diffusion coefficient. In summary, as the preceding observations indicate, the state of computational modelling of PFSA membranes has progressed sufficiently over the last decade to enable its use as a powerful predictive tool with which to guide the process of designing novel membrane materials for fuel cell applications.

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Section: Quantum Chemical Calculationsmentioning

confidence: 99%

Modelling of morphology and proton transport in PFSA membranes

Elliott

Paddison

2007

Phys. Chem. Chem. Phys.

227

255

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“…Short-side-chain ionomers were provided by Shanghai Jia Tong University and synthesized as described previously [12] from CF 2 CF(OCF 2 CF 2 SO 2 F) monomer. Short-side-chain (SSC) PFSA ionomers having IEC (equivalent weight, EW) 1.3 (770), 1.4 (715) and 1.5 meq g −1 (670 g polymer /n SO 3 H ) were used.…”

Section: Methodsmentioning

confidence: 99%

“…Moreover, the enhanced crystallinity enables the preparation of higher IEC PFSA ionomers that do not dissolve or become too gelatinous upon exposure to water. SSC-PFSA ionomer was developed by Dow Chemicals in the mid-1980s, however, due to the complexity and cost of synthesis of the functional monomer further development was abandoned [12]. A simpler route for the synthesis of SSC ionomer was developed and marketed under the trade name Aquivion ® (previously Hyflon ® ) by Solvay Solexis [12].…”

Section: Introductionmentioning

confidence: 99%

“…SSC-PFSA ionomer was developed by Dow Chemicals in the mid-1980s, however, due to the complexity and cost of synthesis of the functional monomer further development was abandoned [12]. A simpler route for the synthesis of SSC ionomer was developed and marketed under the trade name Aquivion ® (previously Hyflon ® ) by Solvay Solexis [12]. SSC-PFSA ionomer membranes (PEMs) have been previously characterised ex situ and in fuel cells [10,[13][14][15], as have theoretical studies aiming to explain the morphology of SSC-PFSA as a function of IEC [16,17].…”

Section: Introductionmentioning

confidence: 99%

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Fuel cell catalyst layers containing short-side-chain perfluorosulfonic acid ionomers

Péron

Edwards

Haldane

et al. 2011

Journal of Power Sources

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Porous catalyst layers (CLs) containing short-side-chain (SSC) perfluorosulfonic acid (PFSA) ionomers of different ion exchange capacity (IEC: 1.3, 1.4 and 1.5 meq g −1 ) were deposited onto Nafion 211 to form catalyst-coated membranes. The porosity of SSC-PFSA-based CLs is larger than Nafion-CL analogues. CLs incorporating SSC ionomer extend the current density of fuel cell polarization curves at elevated temperature and lower relative humidity compared to those based on long-side chain PFSA (e.g., Nafion)-based CLs. Fuel cell polarization performance was greatly improved at 110• C and 30% relative humidity (RH) when SSC PFSI was incorporated into the catalyst layer.Crown

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“…59 Recently, however, Solexis has developed a much simpler (almost a single step for both the fluorination and fluoroolefin addition) route for the synthesis of the same PEM and have reported similar superior performance when compared to Nafion. 64 As discussed earlier, the improved conductance in this SSC PFSA is not currently understood, certainly not on a molecular basis, and is therefore the provocation for the present theoretical investigation.…”

Section: Introductionmentioning

confidence: 99%

Molecular Modeling of the Short-Side-Chain Perfluorosulfonic Acid Membrane

2005

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Presented here is a first principles based molecular modeling investigation of the possible role of the side chain in effecting proton transfer in the short-side-chain perfluorosulfonic acid fuel cell membrane under minimal hydration conditions. Extensive searches for the global minimum energy structures of fragments of the polymer having two pendant side chains of distinct separation (with chemical formula: CF 3 CF(O(CF 2 ) 2 -SO 3 H)(CF 2 ) n CF(O(CF 2 ) 2 SO 3 H)CF 3 , where n ) 5, 7, and 9) with and without explicit water molecules have shown that the side chain separation influences both the extent and nature of the hydrogen bonding between the terminal sulfonic acid groups and the number of water molecules required to transfer the proton to the water molecules of the first hydration shell. Specifically, we have found that fully optimized structures at the B3LYP/6-311G** level revealed that the number of water molecules needed to connect the sulfonic acid groups scaled as a function of the number of fluoromethylene groups in the backbone, with one, two, and three water molecules required to connect the sulfonic acid groups in fragments with n ) 5, 7, and 9, respectively. With the addition of explicit water molecules to each of the polymeric fragments, we found that the minimum number of water molecules required to effect proton transfer also increases as the number of separating tetrafluoroethylene units in the backbone is increased. Furthermore, calculation of water binding energies on CP-corrected potential energy surfaces showed that the water molecules bound more strongly after proton dissociation had occurred from the terminal sulfonic acid groups independent of the degree of separation of the side chains. Our calculations provide a baseline for molecular results that can be used to assess the impact of changes of polymer chemistry on proton conduction, including the side chain length and acidic functional group.

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High Performance Perfluoropolymer Films and Membranes

Cited by 174 publications

References 12 publications

Modelling of morphology and proton transport in PFSA membranes

Modelling of morphology and proton transport in PFSA membranes

Fuel cell catalyst layers containing short-side-chain perfluorosulfonic acid ionomers

Molecular Modeling of the Short-Side-Chain Perfluorosulfonic Acid Membrane

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