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Broka, K.; Ekdunge, P.

doi:10.1023/a:1018469520562

Cited by 332 publications

(209 citation statements)

References 29 publications

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“…This result agrees well with experimental measurements that concluded the same permeability ratio of H 2 and O 2 . 6,7 For the Nafion membrane with a constant water content of λ = 12, the H 2 permeability increases along the adsorbed concentration while that of O 2 stays nearly constant, as shown in Figure 9b. The permeability ratio of H 2 and O 2 increases from 2 at a low gas loading of λ gas = 0.031 25 to 3 at λ gas = 1.125.…”

Section: Gas Permeabilities In Hydrated Nafion Membranementioning

confidence: 87%

“…5 Broka and Ekdunge showed that O 2 permeability through a Nafion 117 membrane increases with temperature and relative humidity or water content and that H 2 permeability is about twice that of O 2 . 6 Moreover, Sakai et al pointed out that the gas permeability of Nafion greatly depends not only on water content but also on cation form and ion-exchange capacity. 7 The observed correlation of H 2 /O 2 permeabilities is in line with the findings from Broka and Ekdunge 6 Molecular simulations have also been extensively applied to study the properties of Nafion membranes.…”

Section: Introductionmentioning

confidence: 99%

“…6 Moreover, Sakai et al pointed out that the gas permeability of Nafion greatly depends not only on water content but also on cation form and ion-exchange capacity. 7 The observed correlation of H 2 /O 2 permeabilities is in line with the findings from Broka and Ekdunge 6 Molecular simulations have also been extensively applied to study the properties of Nafion membranes. 8À13 In these studies, molecular models of Nafion have been successfully developed and experimentally validated in terms of membrane density, Nafion morphology, and water diffusivity.…”

Section: Introductionmentioning

confidence: 99%

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Molecular Simulation of Gas Adsorption, Diffusion, and Permeation in Hydrated Nafion Membranes

et al. 2011

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Molecular simulations were performed to characterize hydrated Nafion membranes in terms of gas adsorption, diffusion, and permeation. The experimental results validate the molecular model of Nafion with respect to material density, morphology, free volume, and water diffusivity. Nafion’s adsorption property is examined in terms of the solubility and adsorption isotherms for gases, including H2, O2, and N2. The adsorption capacity of hydrated Nafion is shown to be strong for O2 and N2 but not for H2. Due to the dilution effect, N2 is able to suppress the loading of O2 and protect the fuel cell from fuel crossover. The dynamic behaviors of H2 and O2 are represented by self-diffusion coefficients, with the results showing that H2 diffusion in Nafion membranes is nearly 1 order of magnitude faster than O2 diffusion. The effects of water content and the concentration of adsorbed gases were verified, and a close correlation of Nafion free volume to gas transport properties was revealed. On the basis of the solution-diffusion mechanism, the permeabilities of H2 and O2 in hydrated Nafion membranes are calculated and compared with corresponding experiments, and the permeability of H2 is found to be approximately twice that of O2.

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Section: Gas Permeabilities In Hydrated Nafion Membranementioning

confidence: 87%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Molecular Simulation of Gas Adsorption, Diffusion, and Permeation in Hydrated Nafion Membranes

et al. 2011

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“…Independentemente, Sakai e Ogumi mostraram que a permeabilidade gasosa ocorre por um mecanismo cooperativo entre a difusão no meio aquoso (fase III) e na matriz hidrofóbica constituída pela fase II no modelo de Yeager [36,37] . No entanto, observa-se um aumento na permeabilidade com o aumento da hidratação do Nafion ® , justificado pela expansão da fase intermediária (fase II) proporcionalmente a hidratação da membrana [40] . Segundo o modelo, a parte intermediária é constituída de uma pequena fração de moléculas de água e, o aumento da hidratação do polímero, leva a uma leve expansão dessa região, permitindo a dissolução de uma maior quantidade dos gases H 2 e O 2 e, conseqüentemente, maior permeabilidade.…”

Section: Permeação De Gasesunclassified

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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“…While the polynomial fit is not rigorous, it does allow ease of use in modeling, especially when one might have to take the derivative of the curve (see section 4.3). A problem with the fit is that it does not take into account the observed lower uptake at higher temperatures (see for example references [146][147][148]), although this can be done with other curve fits or by extrapolating the curve if some data points are known at higher temperatures [149]. Finally, there are some models that use the same approach except use a fourth-order polynomial [86,133].…”

Section: Water Contentmentioning

confidence: 99%