Factors enabling high mobility of protons and water in perfluorosulfonate membranes under low hydration conditions1

Maalouf, Manale; Sun, Che-Nan; Pyle, Brandon; Emery, Michael A.; Haugen, Gregory M.; Hamrock, Steven J.; Zawodzinski, Thomas A.

doi:10.1016/j.ijhydene.2013.11.006

Cited by 29 publications

(27 citation statements)

References 19 publications

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“…In addition, reducing the EW, or backbone length, has been shown to mitigate strong aggregation of ionic domains and improve connectivity. ,− The data presented here indicate that adding acid groups on the side-chain without changing m TFE could effectively reduce EW and lead not only to greater water network connectivity but also a more continuous hydrogen-bonded water structure with enhanced charge delocalization. This is in agreement with previous descriptions of ion transport in PFSAs ,− and PFIAs. , The length scales probed in this study could be integrated with other complementary techniques such as NMR, , which could delineate the ion mobility and water diffusion in MASC ionomers. NMR studies on PFSAs have shown that self-diffusion of water along with relaxation times could be used to probe water transport mechanisms at intermediate length scales, ,− and this could provide additional information on the role of morphology.…”

Section: Results and Discussionsupporting

confidence: 91%

“…68,72 The length-scales probed in this study could be integrated with other complementary techniques such as NMR, 94,95 which could delineate the ion mobility and water diffusion in multi-acid side-chain ionomers. NMR studies on PFSAs have shown that self-diffusion of water along with relaxation times could be used to probe water transport mechanisms at intermediate length-scales, 93,[95][96][97][98] and this could provide additional information on the role of morphology.…”

Section: Connecting Morphology and Chemistrymentioning

confidence: 99%

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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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Section: Results and Discussionsupporting

confidence: 91%

Section: Connecting Morphology and Chemistrymentioning

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 literature is rich with studies on steady-state and transient water diffusion in PFSA membranes (see Figure and Table ) including: steady-state transport measurements, ,,,,,, internal water profiles, ,, gravimetric water uptake, ,,,,,,,,, time-resolved FTIR, ,,, evolution of water-domain spacing using SAXS/SANS, ,,, and XRD . Tracer or self-diffusion is commonly measured using NMR as a function of temperature, ,,,,,,,,− water content, ,,,,,,,,,,,,, cationic form (as discussed in section ), ,,,,− pretreatment and annealing, ,, as well as to investigate various ionomers such as SSC Dow/Aquivion, ,, Flemion, ,,, 3M PFSA, , and Gore-Select Membranes . It should be noted that water transport in this section refers to only water under water gradients (i.e., diagonal components in Table…”

Section: Transport Properties and Mechanismsmentioning

confidence: 99%

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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“…As revealed in Figure a, the C3 method led to the formation of small and uniform hydrophobic domain structures that effectively result in more connected hydrophilic channels when the structure absorbs water. [ 9 ] For Nafion 211 membrane or recast‐PCM, hydrophobic regions with a diameter of 20 nm or more and hydrophilic domains with 20–50 nm were observed. The C3‐PCM sample, on the other hand, consists of much smaller hydrophobic and hydrophilic domains 7–10 nm in size, with these small hydrophilic domains of several nm well connected, forming large domains with lengths of 80 nm.…”

Section: Resultsmentioning

confidence: 99%

Single‐Step Fabrication of Polymeric Composite Membrane via Centrifugal Colloidal Casting for Fuel Cell Applications

Yoon

Lim

et al. 2021

Small Methods

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Recent interest in polymer electrolyte membranes (PEMs) for fuel cell systems has spurred the development of infiltration technology by which to insert ionomers into mechanically robust reinforcement structures by solution casting in order to produce a cost effective and highly efficient electrolyte. However, the results of the fabrication process often continue to present challenges related to the structural complexity and self‐assembly dynamics between the hydrophobic and hydrophilic parts of the constituents which in turn, necessitates additional processing steps and increases production costs. Here, a single‐step process is reported for highly compact polymeric composite membranes (PCMs), fabricated using a centrifugal colloidal casting (C3) method. Combined structural analyses as well as coarse‐grained molecular dynamics simulations are employed to determine the micro‐/macroscopic structural characteristics of the fabricated PCMs. These findings indicate that the C3 method is capable of forming highly dense ionomer matrix–reinforcement composites consisting of microphase‐separated ionomer structures with tailored crystallinity and ionic cluster sizes. An outcome that is very unlikely with the single‐step coating steps in conventional methods. These structural attributes ensure PCMs with better proton conductivity, greater strain stability, and lower gas crossover properties compared to commercial pristine membranes, expanding their possible range of applicability to PEMs.

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Factors enabling high mobility of protons and water in perfluorosulfonate membranes under low hydration conditions1

Cited by 29 publications

References 19 publications

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

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

New Insights into Perfluorinated Sulfonic-Acid Ionomers

Single‐Step Fabrication of Polymeric Composite Membrane via Centrifugal Colloidal Casting for Fuel Cell Applications

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