Determination of water diffusion coefficients in perfluorosulfonate ionomeric membranes

Zawodzinski, Thomas A.; Neeman, Michal; Sillerud, Laurel O.; Gottesfeld, S.

doi:10.1021/j100168a060

Cited by 986 publications

(881 citation statements)

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“…The enhanced proton mobility observed with 4-hydroxy-TEMPO in D 2 O compared to in H 2 O likely arises from a small fraction of 4-hydroxy-TEMPO probing the protons bound to sulfonic acid groups. The estimated D p for the proton near the sulfonic acid groups from the ξ ~270×10 −3 measured with 4-amino-TEMPO is ~ 2.8×10 −9 m 2 s −1 , which is a value comparable to D p ~2×10 −9 m 2 s −1 estimated from conductivity measurements at ~20 water molecules per sulfonic acid [9] While the absolute proton mobility is smaller than in bulk water, not surprisingly, the proton over water diffusivity measured with 4-amino-TEMPO in Nafion yields D p /D w ~ 5 comparable to what is known to be D p /D w = ~ 7 in bulk water with D p ~ 1.7×10 −8 m 2 s −1 [29][30][31] and D w ~2.4×10 −9 m 2 s −1 . [31,32] In contrast, D p /D w is only ~2 for the central region of the water channels as measured with 4-hydroxy-TEMPO.…”

supporting

confidence: 52%

“…(5) in SI) to be 5.3×10 −10 m 2 s −1 , which is comparable to D w ~6×10 −10 m 2 s −1 found by PFG NMR for swollen Nafion with ~20 water molecules per sulfonic acid. [9] In contrast, from τ = 2.2 µs, D w for water molecules in the central region of the water channel is computed to be 6.8×10 −14 m 2 s −1 , i.e. smaller by four orders of magnitude.…”

mentioning

confidence: 83%

“…At a hydration level of ~20 water molecules per sulfonic acid in Nafion 117, a proton diffusion constant (D p ) of ~2×10 −9 m 2 s −1 was estimated by proton conductivity measurements, and a water diffusion constant (D w ) of ~6×10 −10 m 2 s −1 found by pulsed field gradient (PFG) nuclear magnetic resonance (NMR) techniques. [9][10][11][12] Our study takes a new approach by considering the direct influence of Nafion surface chemistry on the local D w and D p , a factor not considered in the literature to date. Ultimately, maximizing local dynamics should directly enhance the macroscopic proton, ion and water transport through PEM, which in turn is a key determinant of fuel cell efficiency.…”

mentioning

confidence: 99%

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

Song

Han

2015

Angewandte Chemie

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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. Keywordselectron paramagnetic resonance spectroscopy; Overhauser dynamic nuclear polarization relaxometry; water and proton dynamics; polymer electrolyte membrane; heterogeneous structure A polymer electrolyte membrane (PEM) placed between a cathode and an anode in a fuel cell, which is a device that converts chemical energy of fuel into electricity through an electrochemical reaction, should be a good conductor for protons but not for electrons and the molecular constituents of the fuel. Nafion's success as PEM stems from the good ionic conductivity through water channels, [1] as well as high chemical and mechanical stability for a wide operating temperature range between 50°C and 100°C. [2] Nafion is composed of a Correspondence to: Oc Hee Han, ohhan@kbsi.re.kr; Songi Han, songi@chem.ucsb.edu. HHS Public Access Author ManuscriptAuthor Manuscript Author ManuscriptAuthor Manuscript poly(tetrafluoroethylene) backbone with side arms decorated with sulfonic acid groups, as illustrated in Figure S1 of Supporting Information (SI). Nafion is known, upon hydration, to swell to form percolated channels through which water, protons and ions diffuse. [3] Nafion's hydrophobic domains are known to have ordered helical fibers with crystallinity similar to that of pure poly(tetrafluoroethylene) at elevated temperatures. [4] However, the exact structure and ordering of the water channels lined by the sulfonic acid groups is still a subject of controversy. Crucially, the channel dimension was found to increase linearly with the water volume fraction [3] indicating locally flat structures of the channels, [5] while scattering patterns are consistent with rod-like shapes for hydrated Nafion membrane at water volume fraction < 50%. [6][7][8] The structure and connectivity of the water channels has been thought to play an important role in the proton and water diffusivity through Nafion membranes, although a firm relationship between structure and transport function has not been established. At a hydration level of ~20 water molecules per sulfonic acid in Nafion 11...

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confidence: 83%

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confidence: 99%

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

Song

Han

2015

Angewandte Chemie

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“…Deviations in the measurements can be attributed to limitations in the weighing and calculation procedures used to determine the content of polymer in the casting solution. Table 2 shows the water content (k) of the membranes following immersion in water and in 1 mol dm -3 H 2 SO 4 at 298 K. The data show that all of the extruded membranes were close to full hydration, which is important in any study of hydrated membrane resistance; it has been shown that a k value of 22 in pure water represents a fully hydrated, extruded Nafion ® membrane [26][27][28][29][30]. A decrease in hydration number is seen when the hydrating solution is changed to 1 mol dm -3 H 2 SO 4 with the membrane water content decreasing by 3-5 mol water per sulphonic acid group.…”

Section: Ion-exchange Capacity Equivalent Weight and Water Contentmentioning

confidence: 99%

The Ionic Conductivity of a Nafion® 1100 Series of Proton‐exchange Membranes Re‐cast from Butan‐1‐ol and Propan‐2‐ol

et al. 2010

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The ionic conductivity of Nafion® 1100 extruded membranes re‐cast from solutions of butan‐1‐ol and propan‐2‐ol is measured in 0.5 mol dm–3 H2SO4 at 295 K, using an immersed, four‐electrode d.c. technique. The general trend is an increasing conductivity for the thicker membranes. Materials which were solution‐cast from butan‐1‐ol yielded the highest conductivity while a series of membranes with lower conductivities (similar to those of an extruded Nafion® 1100 series of membranes) was found using propan‐2‐ol. The conductivity results indicate that membranes manufactured by extrusion and casting from various solvents might have different structures. Differences in the water content and conductivity of the membranes are considered to arise from the impact of processing conditions on the surface and bulk structure of the membranes.

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“…Os tipos de transporte de água mais importantes são o fluxo eletro-osmótico e difusão através da membrana (gradiente de atividade) [9,31] . O fluxo de água através da membrana afeta o desempenho da célula a combustível de três maneiras [29] :…”

Section: Transporte De áGuaunclassified

Propriedades físico-químicas relacionadas ao desenvolvimento de membranas de Nafion® para aplicações em células a combustível do tipo PEMFC

Perles

2008

Polímeros

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Resumo: Embora não seja tecnologia recente, as células a combustível ou Fuel Cells (FC) continuam recebendo grande atenção, pois são consideradas como "fontes de energia do futuro" devido a características como alto rendimento energético e baixa emissão de poluentes, permitindo a extensão o tempo de vida das reservas fósseis e contribuindo para a melhoria da qualidade de vida. Atualmente, as pesquisas estão direcionadas, principalmente, ao desenvolvimento de FC para aplicações em sistemas móveis e portáteis. De todas as tecnologias existentes, a mais promissora para essa finalidade é a célula a combustível de eletrólito polimérico, conhecida como PEMFC (Polymer Electrolyte Fuel Cell) cuja pesquisa encontra-se focada, principalmente, no desenvolvimento de membranas poliméricas, com o objetivo de reduzir os custos de produção. Este trabalho será focado nos aspectos físico-químicos do desenvolvimento de membranas poliméricas. Serão discutidos aspectos estruturais do Nafion ® relacionado-os as seguintes propriedades físico-químicas: fluxo eletrosmótico, permeabilidade gasosa, transporte de água através da membrana, estabilidade química e térmica. Toda a discussão será realizada para polímeros perfluorados, utilizando o Nafion ® como modelo representante dessa classe de polímeros. Palavras-chave: Célula a combustível, membrana polimérica, Nafion ® . Physicochemical Properties Related to the Development of Nafion ® Membranes for Application in Fuel CellsAbstract: Fuel Cells (FC) continue to receive growing attention, in spite of not being a new technology, for they are considered as the "energy source of the future" owing to characteristics such as high energetic yield and low emission of pollutants. FC technology may lead to a reduction in the negative impact from energy sources on the enviroment, thus improving the quality of life and extending the lifetime of fossil combustible reserves. The mainstream of research in FC is now directed at mobile, portable systems, for which the most promising technology is the Polymer Electrolyte Fuel Cells, also known as PEMFC (Polymer Electrolyte Fuel Cell). Research in this topic focuses on the development of polymer membranes whose target is to reduce its production costs. In this work we shall focus on physicochemical aspects related to development of polymeric membranes. A discussion on structural aspects of Nafion ® will be carried, which will be related to the following physicochemical properties: electrosmotic flux, gaseous permeability, water transport through polimeric membrane, chemical and thermal stabilities. All the discussion was made using Nafion ® as model of perfluorated polymers.

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Determination of water diffusion coefficients in perfluorosulfonate ionomeric membranes

Cited by 986 publications

References 1 publication

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

The Ionic Conductivity of a Nafion® 1100 Series of Proton‐exchange Membranes Re‐cast from Butan‐1‐ol and Propan‐2‐ol

Propriedades físico-químicas relacionadas ao desenvolvimento de membranas de Nafion® para aplicações em células a combustível do tipo PEMFC

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