Anion exchange membranes: The effect of reinforcement in water and electrolyte

Luo, Xiaoyan; Kushner, Douglas I.; Kusoglu, Ahmet

doi:10.1016/j.memsci.2023.121945

Cited by 15 publications

(10 citation statements)

References 84 publications

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“…The technique presented here begins to fill this gap by providing missing information on the mesoscale. The ability to obtain and resolve structural information at multiple length scales could provide not only insights into the processing, aging, and thickness effects in relation to dispersion or environmental changes, as discussed in the literature, ,,,− but also a means to eventually tune structure-driven functionality in membranes.…”

Section: Resultsmentioning

confidence: 99%

Revealing Mesoscale Ionomer Membrane Structure by Tender Resonant X-ray Scattering

Rongpipi,

Chan,

Bird

et al. 2024

ACS Appl. Polym. Mater.

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Nafion, a perfluorosulfonic acid ionomer, has been well-studied for decades due to its key role as an ion-conductive membrane in electrochemical energy conversion and storage applications. When hydrated, this membrane phase separates into a complex hierarchical nanostructure with hydrophilic domains that facilitate ion transport. Hard X-ray scattering has been a powerful technique in understanding Nafion due to its capabilities in capturing the ionomer's nanophase separated structure, which gives rise to contrast between polymer and water domains. More recently, resonant X-ray scattering, which tunes to elemental absorption edges to provide specificity on constituent elements, has been explored to highlight key interactions related to the sulfonic acid groups within its structure.Here, we study the Nafion nanostructure by combining hard X-ray scattering and tender resonant X-ray scattering (TReXS) at the sulfur K-edge to reveal a mesoscopic feature corresponding to a correlation length of approximately 40 nm that has been challenging to resolve with hard X-ray studies. Additionally, we study the effect of the dispersion solvent composition that plays a key role in the formation of this mesoscale feature. Notably, TReXS can attain high contrast to decipher this mesoscale morphology even for dry polymer membranes under a vacuum, which typically have reduced contrast for hard X-rays. We find that the correlation length of this mesoscale feature decreases with increasing water fraction in the dispersion, which is the opposite trend exhibited by the smaller intercrystalline feature in the same membranes. This study showcases the utility of TReXS to uncover multiscale morphological details in functional polymers that are not always revealed by other methods like hard X-ray scattering. We illustrate this with Nafion, which is a relevant ion-conducting polymer for electrochemical technologies.

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Section: Resultsmentioning

confidence: 99%

Revealing Mesoscale Ionomer Membrane Structure by Tender Resonant X-ray Scattering

Rongpipi,

Chan,

Bird

et al. 2024

ACS Appl. Polym. Mater.

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“…3,48,63,64 Likewise, water uptake in hydroxide and carbonate forms of Sustainion is available. 21 Figure 3 shows our measurement of water uptake of hydroxide-form Versogen (solid line) as a function of RH, compared to available literature data for carbonate and bicarbonate forms (dashed and dotted lines). 13 Literature results were performed in the same research group in a prior study with procedures consistent with those used in this work.…”

Section: Resultsmentioning

confidence: 99%

“…AEMs studied were Versogen (20 and 80 μm, ∼425 EW, Versogen, Delaware, USA) and Sustainion (X37-50, 50 μm, ∼900 EW, Fuel Cell Store, Colorado, USA). 13, 21 1 M anion solutions determined the membrane ion-exchange form.…”

Section: Experimental Methodsmentioning

confidence: 99%

“…Water-uptake measurements.-Membrane water uptake as a function of RH were taken from previous studies at 25 °C for Nafion in the proton form, for Sustainion in the hydroxide form, and for Sustainion and Versogen in the carbonate and bicarbonate forms. 3,13,21 Water content was assumed to be invariant with temperature, as the impact of temperature on water content for Nafion in the studied temperature range is inconclusive. 3 The water uptake of hydroxide-form Versogen was measured in this study using a dynamic-vapor sorption (DVS) system (Surface Measurement Systems, UK) with the chamber flushed with dry nitrogen gas for 1 h to remove residual CO 2 and set a dry weight prior to the humidification step.…”

Section: Experimental Methodsmentioning

confidence: 99%

“…3 Versogen and Sustainion uptake water similarly to Nafion yielding significant conductivity benefits, but their nanostructures are not well-defined. 13,20,21 Water diffusion has also been studied extensively in Nafion, where values of the diffusion coefficient depend on the measurement technique used, but range from ∼5 × 10 −7 cm 2 /s for steady-state diffusion to ∼10 −5 cm 2 /s using pulse-field nuclear magnetic resonance, and even higher using quasi-elastic neutron scattering, approaching the value of free diffusion in liquid water, ∼5 × 10 −5 cm 2 /s. [22][23][24] Fewer direct measurements exist for AEMs, but initial results suggest a diffusion coefficient of ∼2 × 10 −6 cm 2 /s for Versogen.…”

Section: Comentioning

confidence: 99%

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Electrochemical Measurement of Water Transport Numbers in Anion-Exchange Membranes

Petrovick,

Kushner,

Goyal

et al. 2023

J. Electrochem. Soc.

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Anion-exchange membranes (AEMs) are a possible replacement for perfluorosulfonic-acid membranes in energy-conversion devices, primarily due to the hydroxide mobile ion allowing the devices to operate in alkaline conditions with less expensive electrocatalysts. However, the transport properties of AEMs remain understudied, especially electro-osmosis. In this work, an electrochemical technique, where the open-circuit voltage is measured between two ends of a membrane maintained at different relative humidities, is used to determine the water transport number of various ionomers, including Versogen and Sustainion AEMs and Nafion cation-exchange membrane (CEM), as a function of water content and temperature. In addition, the CEMs and AEMs are examined in differing single-ion forms, specifically proton and sodium (CEM) and hydroxide and carbonate (AEM). Carbonate-form AEMs have the highest transport number (∼11), followed by sodium-form CEMs (∼8), hydroxide-form AEMs (∼6), and proton-form CEMs (∼3). Finally, a multicomponent transport model based on the Stefan-Maxwell-Onsager framework of binary interactions is used to develop a link between water transport number and water-transport properties, extracting a range for the unmeasured membrane water permeability of Versogen as a function of water content.

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Advancements in commercial anion exchange membranes: A review of membrane properties in water electrolysis applications

Wijaya,

Im,

Nam

2024

Desalination and Water Treatment

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Anion exchange membranes: The effect of reinforcement in water and electrolyte

Cited by 15 publications

References 84 publications

Revealing Mesoscale Ionomer Membrane Structure by Tender Resonant X-ray Scattering

Revealing Mesoscale Ionomer Membrane Structure by Tender Resonant X-ray Scattering

Electrochemical Measurement of Water Transport Numbers in Anion-Exchange Membranes

Advancements in commercial anion exchange membranes: A review of membrane properties in water electrolysis applications

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