Nafion in Dilute Solvent Systems: Dispersion or Solution?

Welch, Cynthia F.; Labouriau, Andrea; Hjelm, Rex P.; Orler, Bruce; Johnston, Christina; Kim, Yu Seung

doi:10.1021/mz3005204

Cited by 171 publications

(247 citation statements)

References 25 publications

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“…• C. 26 Browncolored clear dispersions (solid content 2.5 wt%) were obtained. Hydroxide conductivities of the membranes were detemined from AC impedance spectroscopy using a Solartron 1260 gain phase analyzer over a frequency range from 1 Hz to 1 MHz.…”

Section: Methodsmentioning

confidence: 99%

A Microelectrode Study of Interfacial Reactions at the Platinum-Alkaline Polymer Interface

Yim

Chung

Chlistunoff

et al. 2015

J. Electrochem. Soc.

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Hydrogen oxidation (HOR) and oxygen reduction (ORR) reactions at the platinum/alkaline ionomer interface were investigated using two different alkaline polymer electrolytes, i.e., benzyl-trimethyl ammonium tethered poly(phenylene) (ATM-PP) and phenylpentamethyl guanidinium tethered perfluorinated polymer (M-Nafion-FA-TMG). Substantial inhibition of HOR was taking place at the platinum-ATM-PP interface due to the possible cationic group adsorption of ATM-PP, whereas the reaction was virtually unaffected at the platinum-M-Nafion-FA-TMG interface after high anodic potential preconditioning. Moreover, the apparent ORR activity of platinum coated with M-Nafion-FA-TMG was found higher than that in 0.1 M tetra methyl guanidinium solution. In addition, the oxygen permeability of M-Nafion-FA-TMG was found to be ∼2.5 times higher than that of ATM-PP. The above properties of the perfluorinated polymer make it a very promising ionomeric binder for the use in both anode and cathode of alkaline membrane fuel cells. Alkaline membrane fuel cells (AMFCs) have drawn tremendous attention because they have the potential to convert hydrogen fuel to electricity without using precious metal catalysts in the electrodes. 1,2However, the current performances of AMFCs using non-precious or even precious metal catalysts are inferior to those of proton exchange membrane fuel cell (PEMFC) counterparts.3 The inferior performance of AMFCs have been explained by the low hydroxide mobility in anion exchange membranes, 4,5 carbonate/bicarbonate formation, [6][7][8] slow hydrogen oxidation reaction (HOR) kinetics, 9,10 and poor water management.11-13 The differences in performance between AMFCs and PEMFCs are also largely derived from the polymer electrolytes employed in the electrodes that provide different environments for electrochemical reactions and material diffusion.The effects of cation-tethered alkaline polymer electrolytes on AMFC performance have been investigated by several research groups. Varcoe et al. first used a hydroxide conducting ionomer in preparation of alkali metal-cation-free AMFC electrodes.14 There was a substantial increase in the peak power density of AMFCs (55 vs. 1.6 mW cm −2 ) by adding quaternized poly(vinylbenzyl chloride) to the catalyst layers and further improved AMFC performance was reported later using better ionomer dispersion technology, 15 i.e., the peak power density of 185 mW cm −2 . However, the improved AMFC performance was still inferior to the state-of-the-art PEMFC performance. They suggested that relatively low gas permeation by ionomer binder may be the reason for the inferior performance. Researchers from Tokuyama Corporation reported a series of hydroxide conducting ionomers for AMFC applications.16,17 They found that the peak power density of the AMFC performance increased from 22 mW cm −2 to 296 mW cm −2 , as the ion exchange capacity of their hydrocarbon ionomers increased from 0.7 to 1.8 meq. g −1 . They suggested the ionic conductivity of the ionomer is the major factor contributing to the p...

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Section: Methodsmentioning

confidence: 99%

A Microelectrode Study of Interfacial Reactions at the Platinum-Alkaline Polymer Interface

Yim

Chung

Chlistunoff

et al. 2015

J. Electrochem. Soc.

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“…16,17 First, PFSA membranes were converted to the Na + form by placing Nafion 212 in boiling 0.5 M NaOH solution for 90 min. Subsequently, the Na + form membranes were placed in de-ionized water at 80…”

Section: Methodsmentioning

confidence: 99%

The Effect of Cathode Structures on Nafion Membrane Durability

Choi

Langlois

Mack

et al. 2014

J. Electrochem. Soc.

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The effect of cathode structures on the chemical stability of Nafion membranes is investigated. Membrane electrode assemblies (MEAs) were prepared by using Nafion 212 membrane and commercially available carbon supported Pt electro-catalysts. The cathode structures were controlled by the use of long side chain (LSC) and short side chain (SSC) perfluorosulfonic acids (PFSAs) as well as three dispersing solvents for the electrode fabrication (a water-isopropanol mixture, N-methyl-2-pyrrolidone, or glycerol). The membrane durability was evaluated by the H 2 crossover current density after a 200-hour open circuit voltage accelerated stress test. The MEA with a glycerol-processed SSC PFSA-bonded cathode exhibited a 200-fold less H 2 crossover current density than the MEA with a water-isopropanol-processed LSC PFSA-bonded cathodes. The analyzes by electrochemical impedance spectroscopy and microscopy suggest that the structural uniformity of cathodes play the most significant role in the chemical stability of the Nafion membranes. This study emphasizes the importance of cathode structures on the durability of Nafion membranes. Polymer electrolyte membranes (PEMs) are a critical cell component for polymer electrolyte membrane fuel cells (PEMFCs). The durability of PEMs are important because the life of PEMFCs is often determined by PEM failure.1 The chemical stability of PEMs have been discussed since the 1960s, notably by engineers and scientists at GE.2 LaConti proposed a chemical degradation mechanism for perfluorosulfonic acids (PFSAs):3 oxygen molecules permeate through the membrane from the cathode and are reduced at the anode Pt catalyst to form hydrogen peroxide. Although PFSA membranes are stable in the presence of hydrogen peroxide, metal ions such as Fe 2+ and Cu 2+ in the catalyst layers greatly accelerate the membrane degradation rate by forming reactive oxygen species such as hydroxyl (HO·) and hydroperoxyl (HO 2 ·) radicals.Since the reactive oxygen species are generated in the catalyst layer, the membrane degradation is greater with a supply of H 2 and O 2 in the catalyst layers. Liu et al. reported about the substantially short lifetime for Nafion membranes when H 2 and O 2 gases were supplied to the catalyst-coated membrane, while no degradation is detected when H 2 /O 2 is decoupled to H 2 /N 2 or N 2 /O 2 .7 Later, Burlatsky et al. suggested that an extended catalyst layer between the cathode and the membrane could consume reactive oxygen species to produce water, thereby mitigating the membrane degradation. 8 The effect of gas permeability on membrane degradation has been also demonstrated. Sethuraman et al. compared the durability of wholly aromatic membranes, BPSH-35 and Nafion 112, under accelerated stress conditions. 9 Although the BPSH-35 membranes showed poor chemical stability in ex-situ Fenton tests, the membrane electrode assemblies (MEAs) Because the chemical degradation of membranes is related to the formation of reactive oxygen species in the catalyst layers and their access throug...

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“…[2][3][4] Moreover, different high dielectric constant (Ɛ) solvents (including varying water:alcohol ratios) can cause morphology to change dramatically (rods, swollen clusters, random-coil network, etc.). 5 The water-alcohol-PFSA mixture is particularly relevant because it is the typical solvent of commercial dispersions and CL inks. It has been demonstrated that these different solution-phase morphologies directly impact cast film properties; [6][7][8][9][10][11][12][13][14] ionomers maintain a memory of these structures.…”

Section: Introductionmentioning

confidence: 99%

Inherent Acidity of Perfluorosulfonic Acid Ionomer Dispersions and Implications for Ink Aggregation

2018

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Perfluorosulfonic-acid (PFSA) dispersions are used as components in a variety of electrochemical technologies, particularly in fuel-cell catalyst-layer inks. In this study, we characterize dispersions of a common PFSA, Nafion, as well as inks of Nafion and carbon. It is shown that solvent choice affects a dispersion's measured pH, which is found to scale linearly with Nafion loading. Dispersions in water-rich solvents are more acidic than those in propanolrich solvents: a 90% water versus 30% water dispersion can have up to a 55% measured proton deviation. Furthermore, because electrostatic interactions are a function of pH, these differences affect how particles aggregate in solution. Despite having different water contents, all inks studied demonstrate the same particle size and surface charge trends as a function of pH, thus providing insights into the relative influence of solvent and pH effects on these properties.3

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Nafion in Dilute Solvent Systems: Dispersion or Solution?

Cited by 171 publications

References 25 publications

A Microelectrode Study of Interfacial Reactions at the Platinum-Alkaline Polymer Interface

A Microelectrode Study of Interfacial Reactions at the Platinum-Alkaline Polymer Interface

The Effect of Cathode Structures on Nafion Membrane Durability

Inherent Acidity of Perfluorosulfonic Acid Ionomer Dispersions and Implications for Ink Aggregation

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