Water Dynamics in Ionomer Membranes by Field‐Cycling NMR Relaxometry

Perrin, Jean‐Christophe; Lyonnard, Sandrine; Guillermo, Armel; Levitz, Pierre

doi:10.1002/fuce.200500094

Cited by 24 publications

(14 citation statements)

References 10 publications

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“…4͒. This abrupt change most probably indicates the onset of percolation for the hydrophilic domains, i.e., the formation of continuous networklike structure of water paths that promote proton diffusion, 38 a supposition that is also supported by a similarly abrupt A-3͒ to the data. The slower of the two modes is due to interfacial polarization effects, and the faster mode is attributed to the rotation of water/sulfonate groups ͑first hydration shell͒.…”

Section: Resultssupporting

confidence: 60%

State of Water in Perfluorosulfonic Ionomer (Nafion 117) Proton Exchange Membranes

Polizos

Macdonald

et al. 2008

J. Electrochem. Soc.

128

163

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The nature of water in acid-form Nafion 117 was quantified at several hydration levels by dielectric relaxation spectroscopy. Two independent experimental setups were used to collect complex dielectric permittivity spectra at low frequencies ͑0.01 Hz to 1 MHz at −80 to 25°C͒ and in the microwave region ͑0.40-26 GHz at 25-45°C͒. We directly observed the states of water, manifested through three population averages with distinctly resolved dynamical behaviors, and their changes with temperature and hydration level. The fastest process observed was identified as the cooperative picosecond relaxation of free ͑isotropic, bulklike͒ water, whereas the slowest process ͑microsecond relaxation times͒ corresponded to water molecules strongly bound to the charged sulfonic groups. A third type of water was also observed, also characterized by picosecond relaxation times, close to and about three times slower than those of bulk water, which was attributed to loosely bound water and may contain substantial dynamical heterogeneities.

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Section: Resultssupporting

confidence: 60%

State of Water in Perfluorosulfonic Ionomer (Nafion 117) Proton Exchange Membranes

Polizos

Macdonald

et al. 2008

J. Electrochem. Soc.

128

163

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“…The states of water in hydrophilic polymers have been characterized by various methods including DSC and NMR relaxation measurements [14,15,[18][19][20][21][22][23][24][25][26]. Mendil-Jakani et al utilized DSC to study the nature of water in NafionÒ and compared this to water in a disulfonated polyimide that had very short block sequences (average five disulfonated units in a multi-block with five non-sulfonated repeat units) [22].…”

Section: Introductionmentioning

confidence: 99%

States of water in proton exchange membranes: Part A - Influence of chemical structure and composition

Roy

Hickner

Lee

et al. 2017

Polymer

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Disulfonated poly(arylene ether) and polyimide copolymers can phase separate to form nano-scale hydrophilic and hydrophobic domain morphology. Water in these domains has been assigned to three different states, tightly bound, loosely bound and free water. The states of water were characterized using DSC, NMR relaxation and TGA. The chemical structures of the proton exchange membranes were varied in chemical composition, microstructure (random and block) and also regarding functional sulfonic acid groups fixed to the polymer backbones. A strong dependence of the types of water on the ion content and morphology was observed. For the random copolymers, the formation of free water in the system occurs after reaching a certain ion content.

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“…PEMs which allow for systems operating at temperatures above 100°C with the need for lower or even no water management are highly demanded [1]. Especially the effort for the water management, which is a consequence of water-swollen membranes and the water dynamics related to it, is a major draw-back of currently used PEMs [2]. Also in Direct Methanol Fuel Cells (DMFC), the perfluorinated ionomer-based membranes exhibit a particularly poor performance, because methanol crossover is their major problem besides their low operation temperature [3].…”

Section: Introductionmentioning

confidence: 99%

Anhydrous Polymeric Proton Conductors Based on Imidazole Functionalized Polysiloxane

et al. 2006

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Intrinsically proton conducting polymers with imidazole as proton solvent tethered to a polysiloxane backbone via a flexible spacer have been synthesized. Apart from the standard characterization also their thermal properties and transport behavior have been investigated. The materials exhibit proton conductivity as a consequence of self‐dissociation of the imidazole moieties and “structure diffusion” of the resulting defects. In particular, no liquid phase such as water or monomeric imidazole is needed for the observed proton conductivities.To study the influence of the tether structure on the transport properties, cyclic oligomers and open chain polymers with different spacer lengths have been synthesized.The materials are thermally stable up to 200 °C and become soft around room temperature. The conductivity exhibits VTF and WLF behavior with maximum conductivities around σ = 1.5.10–3 S cm–1 at T = 160 °C. The activation volume of the conductivity as derived from pressure dependent measurements is found to be unusually high. The lowest activation volumes and the highest conductivities are observed for the materials with the highest segmental mobilities, i.e. the longest spacers.Proton self‐diffusion coefficients as obtained from PFG NMR diffusion measurements are significantly higher than expected from the proton conductivities obtained by dielectric spectroscopy. This corresponds to unusually high Haven ratios which have been interpreted by correlated proton transfers allowing for fast proton diffusion while minimizing the separation of ionic charge carriers.

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Water Dynamics in Ionomer Membranes by Field‐Cycling NMR Relaxometry

Cited by 24 publications

References 10 publications

State of Water in Perfluorosulfonic Ionomer (Nafion 117) Proton Exchange Membranes

State of Water in Perfluorosulfonic Ionomer (Nafion 117) Proton Exchange Membranes

States of water in proton exchange membranes: Part A - Influence of chemical structure and composition

Anhydrous Polymeric Proton Conductors Based on Imidazole Functionalized Polysiloxane

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