Thermodynamics and Proton Transport in Nafion

Choi, Pyoungho; Jalani, Nikhil H.; Datta, Ravindra

doi:10.1149/1.1859814

Cited by 382 publications

(255 citation statements)

References 72 publications

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“…47,48 In this case, the cation transport number corresponded to the proton transport (t H+ ), since it was determined from the membrane potential (∆ mem ) measurements performed with HCl solutions. Fig.…”

Section: Electrochemical Characterizationmentioning

confidence: 99%

Chemical and electrochemical characterization of Nafion containing silver nanoparticles in a stripe-like distribution

et al. 2016

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The particular chemical structure of Nafion with nanostructured and segregated hydrophilic and hydrophobic domains enables its use as a model structure for the manufacture of polymer-metal nanocomposites. Among such nanocomposites, samples of Nafion-117 containing Ag-NPs of ca. 10 nm prepared by Intermatrix Synthesis exhibited a particular distribution in the form of stripes, a regular pattern that could reveal the real morphology of the polymer. To evaluate the potential application of this engineered material (e.g. in electrochemical devices), these new nanocomposite membranes were characterized by different techniques: microscopic, surface chemical analysis, mechanical and electrical/electrochemical. X-Ray (XRD and XPS) analyses combined with synchrotron experiments (XANES) were used to determine the chemical speciation of Ag in the membrane. Membrane potential and impedance spectroscopy measurements showed that such Ag-NPs did not hinder the diffusive transport of protons in the membrane bulk, moreover, they slightly reduced the electrical resistance in fully hydrated state samples. The mechanical evaluation of the nanocomposite evidenced the reduction of the elastic character when compared with the unmodified Nafion-117 sample.

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Section: Electrochemical Characterizationmentioning

confidence: 99%

Chemical and electrochemical characterization of Nafion containing silver nanoparticles in a stripe-like distribution

et al. 2016

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“…This mismatch between oxygen and 30 proton transport pathways, resulting in proton depletion at the three-phase boundary can also be a major issue in fuel cells, particularly as proton transport in proton exchange membranes is much slower than in aqueous electrolytes. 51 The SECCM technique described provides an effective way to investigate such 35 an effect. Importantly, we demonstrate that it is possible to obtain approximate kinetic parameters for individual high-index grains in a semi-quantitative manner with a simple kinetic analysis.…”

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confidence: 99%

High resolution mapping of oxygen reduction reaction kinetics at polycrystalline platinum electrodes

Chen

Meadows

Cuharuc

et al. 2014

Phys. Chem. Chem. Phys.

111

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The scanning droplet-based technique, scanning electrochemical cell microscopy (SECCM), combined with electron backscatter diffraction (EBSD), is demonstrated as a powerful approach for visualizing surface structure effects on the rate of the oxygen reduction reaction (ORR) at polycrystalline platinum electrodes. Elucidating the effect of electrode structure on the ORR is of major interest in connection to 10 electrocatalysis for energy-related applications. The attributes of the approach herein stem from: (i) the ease with which the polycrystalline substrate electrode can be prepared; (ii) the wide range of surface character open to study; (iii) the possibility of mapping reactivity within a particular facet (or grain), in a pseudo-single crystal approach, and acquiring a high volume of data as a consequence; (iv) the ready ability to measure the activity at grain boundaries; and (v) an experimental arrangement (SECCM) that 15 mimics the three-phase boundary in low temperature fuel cells. The kinetics of the ORR was analyzed and a finite element model was developed to explore the effect of the three-phase boundary, in particular to examine pH variations in the droplet and the differential transport rates of the reactants and products. We have found a significant variation of activity across the platinum substrate, inherently linked to the crystallographic orientation, but do not detect any enhanced activity at grain boundaries. Grains with 20 (111) and (100) contributions exhibit considerably higher activity than those with (110) and (100) contributions. These results, which can be explained by reference to previous single crystal measurements, enhance our understanding of ORR structure-activity relationships on complex high-index platinum surfaces, and further demonstrate the power of high resolution flux imaging techniques to visualize and understand complex electrocatalyst materials.

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“…A formação e quebra dessas ligações, promove o deslocamento do centro de simetria desses complexos no espaço e, conseqüentemente, o centro da região com excesso protônico. Devido a redução da constante dielétrica (ε) das moléculas de água de hidratação dos grupos sulfonatos, o excesso de prótons é mais estável no centro dos poros e canais do que na região interfacial [10,11,26,28,29] .…”

Section: Nafion ®unclassified

“…Com isso, a difusão de pró-tons ocorre através desses canais pelos mesmos mecanismos pelos quais ocorre em água pura. Portanto, a condutividade é dependente da química do próton e é normalmente explicada através de dois mecanismos de difusão já bastante conhecidos pelos químicos [8,10,11,26,27] . São eles: I) difusão estrutural (mecanismo de Grotthuss) e II) difusão veicular.…”

Section: Nafion ®unclassified

“…Essa interação com os grupos -SO 3 -, que é mais forte para moléculas de água na camada de hidratação dos H + , faz com que parte destas moléculas de água de hidratação fiquem "aderidas" nas paredes ao longo do caminho de arraste, resultando em menores valores de K drag em menores valores de λ (moléculas de H 2 O/H + ). Porém, em altos graus de hidratação (λ > 13 moléculas de água/-SO 3 H), as espécies H(H 2 O) n + tendem a se concentrar na região central desses canais, distantes dos grupos -SO 3 -e, conseqüentemente, são observados altos valores de K drag , pois menos moléculas de água ficam aderidas nas paredes dos canais ao longo do caminho de arraste [26,33,34] . Portanto, o valor de K drag cresce até um limite máximo em função do aumento da hidratação da membrana.…”

Section: Efeito Da Hidrataçãounclassified

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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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Thermodynamics and Proton Transport in Nafion

Cited by 382 publications

References 72 publications

Chemical and electrochemical characterization of Nafion containing silver nanoparticles in a stripe-like distribution

Chemical and electrochemical characterization of Nafion containing silver nanoparticles in a stripe-like distribution

High resolution mapping of oxygen reduction reaction kinetics at polycrystalline platinum electrodes

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

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