Nanometer-Scale Water- and Proton-Diffusion Heterogeneities across Water Channels in Polymer Electrolyte Membranes

Nafion, the most widely used polymer for electrolyte membranes (PEMs) in fuel cells, consists of a fluorocarbon backbone and acidic groups that, upon hydration, swell to form percolated channels through which water and ions diffuse. Although the effects of the channel structures and the acidic group...

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Bibliographic Details
Published in:Angewandte Chemie 2015-03, Vol.127 (12), p.3686-3691
Main Authors: Song, Jinsuk, Han, Oc Hee, Han, Songi
Format: Article
Language:eng ; ger
Subjects:
Channels
Chemistry
Diffusion
Diffusivity
Dynamische Kernpolarisation
Electrolytes
EPR-Spektroskopie
Fluorocarbons
Fuel cells
Heterogene Struktur
Heterogeneity
Ion transport
Membranes
Perfluorocarbons
Polymerelektrolytmembranen
Surface chemistry
Wasser/Protonen-Dynamik
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Summary:Nafion, the most widely used polymer for electrolyte membranes (PEMs) in fuel cells, consists of a fluorocarbon backbone and acidic groups that, upon hydration, swell to form percolated channels through which water and ions diffuse. Although the effects of the channel structures and the acidic groups on water/ion transport have been studied before, the surface chemistry or the spatially heterogeneous diffusivity across water channels has never been shown to directly influence water/ion transport. By the use of molecular spin probes that are selectively partitioned into heterogeneous regions of the PEM and Overhauser dynamic nuclear polarization relaxometry, this study reveals that both water and proton diffusivity are significantly faster near the fluorocarbon and the acidic groups lining the water channels than within the water channels. The concept that surface chemistry at the (sub)nanometer scale dictates water and proton diffusivity invokes a new design principle for PEMs. Die Wasser/Protonen‐Diffusivität in der unmittelbaren Umgebung (1 nm) einer in spezifischen heterogenen Regionen einer Nafion‐Polymerelektrolytmembran (PEM) lokalisierten Spinsonde war deutlich schneller nahe dem Fluorkohlenstoff und den acidischen Gruppen, die die Wasserkanäle bilden, als innerhalb der Wasserkanäle (siehe Bild). Demzufolge bestimmt die Oberflächenchemie auf der Nanometerskala die Transporteigenschaften in PEMs.
ISSN:0044-8249
1521-3757
DOI:10.1002/ange.201408318