Proton Exchange Membrane Fuel Cells: High-Temperature, Low-Humidity Operation

Hamrock, Steven J.; Herring, Andrew M.

doi:10.1007/978-1-4419-0851-3_155

Cited by 7 publications

(18 citation statements)

References 67 publications

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“…For example, 3M PFSA has a shorter-side chain compared to Nafion, but it is not known as an SSC, which usually indicates Dow/Aquivion PFSA.] As seen in Figure , the PFSA ionomers with shorter-side chains and higher IECs have been increasingly studied, − due to their increased transport properties and performance in devices. − , It is not just the length of the side-chain but also its chemistry that governs a PFSA’s properties, which could be even more relevant and important when studying the ionomers in a dispersion state or the interfaces they form with the other materials (such as thin films or in electrode structures).…”

Section: Introductionmentioning

confidence: 99%

“…Even though the most commonly studied PFSA is 1100 EW Nafion, which dominates the published property data sets, the impact of EW on membrane properties and structure have always been of an interest, yet overlooked, in part due to the lack of a wide range of EWs among commercially available PFSAs. Earlier studies by researchers at DuPont reported properties of Nafion of various EWs, including, nanostructure, crystallinity, water uptake, and conductivity. − These were followed by similar studies on the effect of EW on PFSA’s swelling and structure–property relationship, − including those of shorter side-chain (SSC Dow) PFSAs. − Relatively more recent investigations on EW and side-chain effects include investigation of water uptake, ,,,− morphology, ,,,,, conductivity, diffusion and other transport properties, ,− ,,,,,,− thermal and mechanical properties, − ,,,,,, and molecular modeling and simulations. − More recent studies have moved toward exploring alternative PFSA chemistries, such as multiacid ionomers containing multiple acid groups per side-chain (e.g., based on aromatic sulfonic acids (ortho bis acid) or perfluorinated side-chains (perfluoro imide acids, or PFIAs). ,,,, and additives and reinforce...…”

Section: Introductionmentioning

confidence: 99%

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New Insights into Perfluorinated Sulfonic-Acid Ionomers

2017

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In this comprehensive review, recent progress and developments on perfluorinated sulfonic-acid (PFSA) membranes have been summarized on many key topics. Although quite well investigated for decades, PFSA ionomers' complex behavior, along with their key role in many emerging technologies, have presented significant scientific challenges but also helped create a unique cross-disciplinary research field to overcome such challenges. Research and progress on PFSAs, especially when considered with their applications, are at the forefront of bridging electrochemistry and polymer (physics), which have also opened up development of state-of-the-art in situ characterization techniques as well as multiphysics computation models. Topics reviewed stem from correlating the various physical (e.g., mechanical) and transport properties with morphology and structure across time and length scales. In addition, topics of recent interest such as structure/transport correlations and modeling, composite PFSA membranes, degradation phenomena, and PFSA thin films are presented. Throughout, the impact of PFSA chemistry and side-chain is also discussed to present a broader perspective.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

New Insights into Perfluorinated Sulfonic-Acid Ionomers

2017

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“…The degree of this phase separation in response to hydration is primarily influenced by the ionomer chemistry, including the number of TFE repeat units in the backbone between side-chains, m TFE , and the nature of the ionic groups and side-chain (Figure ). ,− Side-chain chemistry and m TFE collectively control a perfluorinated ionomer’s equivalent weight (EW), the grams of dry polymer per mole of ionic group, which is inversely proportional to the ion-exchange capacity (IEC). The higher the EW, the lower the uptake and conductivity, all other factors being equal. , Thus, ionomer EW dictates hydration and transport properties, mechanical stability, and ultimately its morphology and structure–function relationships.…”

Section: Introductionmentioning

confidence: 99%

“…In this case, starting with the same sulfonyl fluoride polymer, the PFSA generated would have an EW of 825 g/mol, but the PFIA would have an EW of 620 g/mol. This novel ionomer is being developed by 3M because of its notably higher proton conductivity at lower relative humidity (RH) than the parent PFSA, which results in improved performance in fuel cells under dry-hot conditions, ,− albeit with possible stability issues as its side-chain is prone to chemical degradation. ,, Despite recent studies on PFIA (PFICE-2), how this new bis(sulfonyl)imide group changes the hydration and structure-transport interplay in PFICE ionomers compared to PFSAs remains an open question. The disordered nanomorphology of PFSA ionomers, which is characterized by a broad ionomer peak in small-angle X-ray scattering (SAXS) experiments, makes it challenging to accurately establish hydration-dependent structure transport relationships .…”

Section: Introductionmentioning

confidence: 99%

Chemical and Morphological Origins of Improved Ion Conductivity in Perfluoro Ionene Chain Extended Ionomers

Cordova

Yandrasits

et al. 2019

J. Am. Chem. Soc.

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The performance of ion-conducting polymer membranes is complicated by an intricate interplay between chemistry and morphology that is challenging to understand.Here, we report on perfuoro-ionene chain extended (PFICE) ionomers that contain either one or two bis(sulfonyl)imide groups on the side-chain in addition to a terminal sulfonic acid group. PFICE ionomers exhibit greater water uptake and conductivity compared to prototypical perfluorinated sulfonic acid ionomers. Advanced in situ synchrotron characterization reveals insights into the connections between molecular structure and morphology that dictate performance. Guided by first-principles 1 calculations, X-ray absorption spectroscopy at the sulfur K-edge can discern distinct protogenic groups and be sensitive to hydration level and configurations that dictate proton dissociation. In situ resonant X-ray scattering at the sulfur K-edge reveals that PFICE ionomers have a phase-separated morphology with enhanced short-range order that persists in both dry and hydrated states. The enhanced conductivity of PFICE ionomers is attributed to a unique multi-acid side-chain chemistry and structure that facilitates proton dissociation at low water content in combination with a well-ordered phase-separated morphology with nanoscale transport pathways. Overall, these results provide insights for the design of new ionomers with tunable phase-separation and improved transport properties and demonstrate the efficacy of X-rays with elemental sensitivity for unraveling structural features in chemically-heterogeneous functional materials for electrochemical energy applications.

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“…The lower proton conductivity of the electrolyte membranes made of poly(vinylbenzyl sulfonic acid)-grafted FEP in this study, compared to that of perfluorosulfonic acid (PFSA) membranes such as Nafion 212 and the 3M 825EW, can be attributed to the fact that in general, the acid strength of the PFSA SO 3 H is stronger than that of an aromatic SO 3 H (pK a ≈ –6 vs. ≈ –3). In addition, the PFSA may undergo phase separation into very distinct ionic channels and fluoropolymer matrix, while the sulfonated hydrocarbons have less tendency to undergo phase separation (52, 53).…”

Section: Discussionmentioning

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 Membrane Fuel Cells: High-Temperature, Low-Humidity Operation

Cited by 7 publications

References 67 publications

New Insights into Perfluorinated Sulfonic-Acid Ionomers

New Insights into Perfluorinated Sulfonic-Acid Ionomers

Chemical and Morphological Origins of Improved Ion Conductivity in Perfluoro Ionene Chain Extended Ionomers

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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