title: Nanometer-scale water- and proton-diffusion heterogeneities across water channels in polymer electrolyte membranes.
abstract: 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.
authors: Department of Chemistry and Biochemistry, University of California, Santa Barbara, Santa Barbara, CA 93106 (USA).
authors: Jinsuk
authors: J
authors: Song
authors: Oc Hee
authors: OH
authors: Han
authors: Songi
authors: S
authors: Han
mesh_terms: D004058:Diffusion; D004573:Electrolytes / Q000737:chemistry*; D004578:Electron Spin Resonance Spectroscopy; D005465:Fluorocarbon Polymers / Q000737:chemistry; D005466:Fluorocarbons / Q000737:chemistry; D008567:Membranes, Artificial; D049329:Nanostructures / Q000737:chemistry*; D011108:Polymers / Q000737:chemistry*; D011522:Protons; D014867:Water / Q000737:chemistry
chemical_list: D004573:Electrolytes; D005465:Fluorocarbon Polymers; D005466:Fluorocarbons; D008567:Membranes, Artificial; D011108:Polymers; D011522:Protons; D014867:Water; C040402:perfluorosulfonic acid
keywords: EPR spectroscopy; Overhauser dynamic nuclear polarization; heterogeneous structures; polymer electrolyte membranes; water/proton dynamics
references: Biochemistry. 2002 Feb 5;41(5):1464-73
references: 11814339
references: J Am Chem Soc. 2011 Dec 14;133(49):19953-9
references: 22023139
references: J Phys Chem B. 2009 Oct 22;113(42):13935-41
references: 19791737
references: Biophys J. 1997 Nov;73(5):2575-9
references: 9370451
references: Biophys J. 2010 Sep 8;99(5):1604-10
references: 20816073
references: Biophys J. 2006 Oct 1;91(7):2647-64
references: 16844740
references: J Gen Physiol. 1997 Apr;109(4):415-34
references: 9101402
references: Chem Rev. 2004 Oct;104(10):4535-85
references: 15669162
references: Biochim Biophys Acta. 2006 Aug;1757(8):886-912
references: 16934216
references: Nat Mater. 2011 Jun 19;10(7):507-11
references: 21685901
references: Biochemistry. 1996 Jun 18;35(24):7692-704
references: 8672470
references: Nat Mater. 2008 Jan;7(1):75-83
references: 18066069
references: J Phys Chem B. 2011 Mar 31;115(12):2717-27
references: 21370837