NMR Investigation of the Dynamics of Confined Water in Nafion-Based Electrolyte Membranes at Subfreezing Temperatures

Nicotera, Isabella; Coppola, Luigi; Rossi, Cesare Oliviero; Youssry, Mohamed; Ranieri, Giuseppe Antonio

doi:10.1021/jp904691g

Cited by 50 publications

(65 citation statements)

References 28 publications

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“…water in swollen Nafion, which range from a few to hundreds of milliseconds. [26,27] This result confirms that the modulation in the x value is not influenced by the intrinsic nuclear-spin relaxation, but by the dynamics of water. From t = 280 ps, the D w value for water molecules near sulfonic acid was computed to be 5.3 10 À10 m 2 s À1 (see equation (5) in the Supporting Information), which is comparable to D w % 6 10 À10 m 2 s À1 found by PFG NMR spectroscopy for swollen Nafion with approximately 20 water molecules per sulfonic acid group.…”

Section: Methodssupporting

confidence: 74%

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

Song

Han

2015

Angew Chem Int Ed

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Nafion, the most widely used polymer for electrolyte membranes (PEM) in fuel cells, consists of fluorocarbon backbones and acidic groups that, upon hydration, swell to form percolated channels through which water and ions diffuse. While 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. Using molecular spin probes that selectively partition into heterogeneous regions of 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 compared to 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 PEM.

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Section: Methodssupporting

confidence: 74%

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

Song

Han

2015

Angew Chem Int Ed

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“…This value compares to a water self‐diffusion coefficient of ∼2 × 10 −10 m 2 s −1 at 273 K. Although this work demonstrates that absorbed water in PFSAs was moving more slowly in the membranes below 0 °C compared to membranes at higher temperatures, there was enough mobility to promote proton transport. Other studies of water mobility at low temperatures showed step changes in the water self‐diffusion coefficient at low temperatures that were attributed to freezing events 47, 48. These membranes were probably more hydrated than the samples studied by Ma et al, which lead to some portion of the water in the membrane freezing.…”

Section: Water Motion and Proton Conductivitymentioning

confidence: 77%

Water‐mediated transport in ion‐containing polymers

Hickner

2011

J Polym Sci B Polym Phys

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Water-mediated ion conduction enables high conductivity in hydrated polymer membranes commonly used in electrochemical devices. Understanding the coupling of the absorbed water with the polymer matrix and the dynamics of water inside the polymer network across the full range of length scales in the membrane is important for unraveling the structure-property relationships in these materials. By considering the water behavior in ion-containing polymers, next-generation fuel cell membranes are being designed that exceed the conductivity of the state-of-the-art materials and have optimized conductivity and permeability that may be useful in other types of devices such as redox flow batteries. Waterpolymer associations can be exploited to tune the transport and mechanical property tradeoffs in these polymers. Measurements of water motion provide important criteria for assessing the factors that control the performance of these types of materials. This review article discusses current understanding of water behavior in ion-containing polymers and the relationship between water motion and ion and molecular transport.

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“…16,27 In the model fits to the experimental data of Nafion/DTA þ and Nafion/TMPA þ systems, the contributions of R and SD are not presented separately but are represented by a single curve (R 1 ) RþSD = (R 1 ) R þ (R 1 ) SD , with a prefactor (R 1 ) 0 RþSD and a single correlation time τ c . In Figure 9a,b are presented the best fits obtained with eq 3 to the R 1 experimental results obtained for the Nafion/DTA þ and Nafion/TMPA þ systems.…”

Section: Articlementioning

confidence: 99%

Proton NMR Relaxometry Study of Nafion Membranes Modified with Ionic Liquid Cations

et al. 2011

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Proton nuclear magnetic resonance (NMR) relaxometry was used to study the ionic mobility and levels of confinement within Nafion membranes modified by incorporation of selected ionic liquid (IL) cations. These studies were performed aiming at understanding the effect of using different types of ionic liquid cations, and their degree of incorporation, in the values of the spin-lattice relaxation times (T(1)) obtained at different values of frequency and thus detect the influence of confinement level on the ions mobility. The frequency dependence of the proton spin-lattice relaxation rate, R(1) = 1/T(1), for the modified Nafion/IL cation membranes was compared with that obtained for an unmodified Nafion membrane, allowing for distinguishing different contributions of the motions of the molecules depending on the frequency tested. The experimental R(1) results were analyzed in terms of models that consider the sum of the most effective relaxation contributions, to estimate the translational self-diffusion coefficient of the moving molecular species in the modified membranes. The stability of these membranes with temperature in terms of the spin-lattice relaxation was compared with results obtained by thermogravimetric analysis.

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NMR Investigation of the Dynamics of Confined Water in Nafion-Based Electrolyte Membranes at Subfreezing Temperatures

Cited by 50 publications

References 28 publications

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

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

Water‐mediated transport in ion‐containing polymers

Proton NMR Relaxometry Study of Nafion Membranes Modified with Ionic Liquid Cations

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