Proton Exchange Membranes for High Temperature Fuel Cells: Equivalent Weight and End Group Effects on Conductivity

Maalouf, Manale; Pyle, Brandon; Sun, Che-Nan; Wang, Dongsheng; Paddison, Stephen J.; Schaberg, Mark S.; Emery, Michael A.; Lochhaas, Kai Helmut; Hamrock, Steven J.; Ghassemi, Hossein; Zawodzinski, Thomas A.

doi:10.1149/1.3210704

Cited by 19 publications

(11 citation statements)

References 4 publications

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“…It is difficult to compare the experimental diffusion of 3M and Hyflon, as there is no published diffusion data for 3M. However, the trend seen here is what one would expect from experiment, since 3M shows greater conductivity than Hyflon, but the expected magnitude of the difference is again not captured. , …”

Section: Resultsmentioning

confidence: 57%

Proton Transport Mechanism of Perfluorosulfonic Acid Membranes

2014

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An understanding of proton transport within perfluorosulfonic acid (PFSA) membranes is crucial to improve the efficiency of proton exchange membrane fuel cells. Using reactive molecular dynamics simulations, we have examined proton transport in two PFSA materials, Hyflon and the 3M membrane, at three different hydration levels. The interaction between the sulfonate group of the polymer side chains and the hydrated protons was found to have only a small influence on the proton transport dynamics. Instead, proton swapping between sulfonate groups is the primary transport mechanism for the proton transport within the pore. The larger water clusters and more flexible side chain of the 3M membrane allows for an enhancement of this swapping mechanism compared to Hyflon. Membranes that can enhance this mechanism may result in greater proton conductivity.

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Section: Resultsmentioning

confidence: 57%

Proton Transport Mechanism of Perfluorosulfonic Acid Membranes

2014

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“…However, there have been some studies on the macroscopic behavior of membranes that suggest that a smaller equivalent weight is preferable. 13,62,63 It has been shown that multiple proton mobility mechanisms contribute to the overall proton transport ability of a fuel cell membrane. 64,65 The most efficient manner in which protons diffuse is through the Grotthuss mechanism, as is true for bulk water.…”

Section: Resultsmentioning

confidence: 99%

“…3MC has a larger α value and a larger equivalent weight (see Table ), which is fewer sulfonate head groups per polymer length. However, there have been some studies on the macroscopic behavior of membranes that suggest that a smaller equivalent weight is preferable. ,, It has been shown that multiple proton mobility mechanisms contribute to the overall proton transport ability of a fuel cell membrane. , The most efficient manner in which protons diffuse is through the Grotthuss mechanism, as is true for bulk water. − In addition to this mechanism, proton hopping at the interface between water and the negatively charged head groups that line the wall of the channel as well as the mass diffusion of the water molecules can contribute to proton mobility. ,, Also of note, the 3MC membrane has a steady-state spectrum that is most like that of bulk water, and it also has the proton transfer exponent, α, that is closest to that of bulk water. These results indicate that water in 3MC membrane nanochannels when swelled to saturation is most like bulk water compared with water in 3MB or Nafion channels.…”

Section: Resultsmentioning

confidence: 99%

Proton Transfer in Perfluorosulfonic Acid Fuel Cell Membranes with Differing Pendant Chains and Equivalent Weights

2017

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Proton transfer in the nanoscopic water channels of polyelectrolyte fuel cell membranes was studied using a photoacid, 8-hydroxypyrene-1,3,6-trisulfonic acid sodium salt (HPTS), in the channels. The local environment of the probe was determined using 8-methoxypyrene-1,3,6-trisulfonic acid sodium salt (MPTS), which is not a photoacid. Three fully hydrated membranes, Nafion (DuPont) and two 3M membranes, were studied to determine the impact of different pendant chains and equivalent weights on proton transfer. Fluorescence anisotropy and excited state population decay data that characterize the local environment of the fluorescent probes and proton transfer dynamics were measured. The MPTS lifetime and anisotropy results show that most of the fluorescent probes have a bulk-like water environment with a relatively small fraction interacting with the channel wall. Measurements of the HPTS protonated and deprotonated fluorescent bands' population decays provided information on the proton transport dynamics. The decay of the protonated band from ∼0.5 ns to tens of nanoseconds is in part determined by dissociation and recombination with the HPTS, providing information on the ability of protons to move in the channels. The dissociation and recombination is manifested as a power law component in the protonated band fluorescence decay. The results show that equivalent weight differences between two 3M membranes resulted in a small difference in proton transfer. However, differences in pendant chain structure did significantly influence the proton transfer ability, with the 3M membranes displaying more facile transfer than Nafion.

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“…Temperature and relative humidity were controlled using a temperature/humidity chamber (model no. 1007H; TestEquity LLC, Moorpark, CA) (36). Measurements of conductivity were taken at 80°C with 10% intervals where the relative humidity cycled from an initial relative humidity of 70% to 20%, then to 90%.…”

Section: Methodsmentioning

confidence: 99%

Mechanisms and Characterization of the Pulsed Electron-Induced Grafting of Styrene onto Poly(tetrafluoroethylene-co-hexafluoropropylene) to Prepare a Polymer Electrolyte Membrane

et al. 2018

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During the pulsed-electron beam direct grafting of neat styrene onto poly(tetrafluoroethylene-co-hexafluoropropylene) (FEP) substrate, the radiolytically-produced styryl and carbon-centered FEP radicals undergo various desired and undesired competing reactions. In this study, a high-dose rate is used to impede the undesired free radical homopolymerization of styrene and ensure uniform covalent grafting through 125-μm FEP films. This outweighs the enhancement of the undesired crosslinking reactions of carbon-centered FEP radicals and the dimerization of the styryl radicals. The degree of uniform grafting through 125-μm FEP films increases from ≈8%, immediately after pulsed electron irradiation to 33% with the subsequent thermal treatment exceeding the glass transition temperature of FEP of 39°C. On the contrary, steady-state radiolysis using Co gamma radiolysis, shows that the undesired homopolymerization of the styrene has become the predominant reaction with a negligible degree of grafting. Time-resolved fast kinetic measurements on pulsed neat styrene show that the styryl radicals undergo fast decays via propagation homopolymerization and termination reactions at an observed reaction rate constant of 5 × 10 l · mol · s. The proton conductivity of 25-μm film at 80°C is 0.29 ± 0.01 s cm and 0.007 s cm at relative humidity of 92% and 28%, respectively. The aims of this work are: 1. electrolyte membranes are prepared via grafting initiated by a pulsed electron beam; 2. postirradiation heat-treated membranes are uniformly grafted, ideal for industry; 3. High dose rate is the primary parameter to promote the desired reactions; 4. measurement of kinetics of undesired radiation-induced styrene homopolymerization; and 5. The conductivity of prepared membranes is on par or higher than industry standards.

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Proton Exchange Membranes for High Temperature Fuel Cells: Equivalent Weight and End Group Effects on Conductivity

Cited by 19 publications

References 4 publications

Proton Transport Mechanism of Perfluorosulfonic Acid Membranes

Proton Transport Mechanism of Perfluorosulfonic Acid Membranes

Proton Transfer in Perfluorosulfonic Acid Fuel Cell Membranes with Differing Pendant Chains and Equivalent Weights

Mechanisms and Characterization of the Pulsed Electron-Induced Grafting of Styrene onto Poly(tetrafluoroethylene-co-hexafluoropropylene) to Prepare a Polymer Electrolyte Membrane

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