Highly Permeable Perfluorinated Sulfonic Acid Ionomers for Improved Electrochemical Devices: Insights into Structure-Property Relationships

Rapid improvements in polymer-electrolyte fuel-cell (PEFC) performance have been driven by the development of commercially available ion-conducting polymers (ionomers) that are employed as membranes and catalyst binders in membrane-electrode assemblies. Commercially available ionomers are based on a perfluorinated chemistry comprised of a polytetrafluoroethylene (PTFE) matrix that imparts low gas permeability and high mechanical strength but introduces significant mass-transport losses in the electrodes. These transport losses currently limit PEFC performance, especially for low Pt loadings. In this study, we present a novel ionomer incorporating a glassy amorphous matrix based on a perfluoro(2-methylene-4-methyl-1,3-dioxolane) (PFMMD) backbone. The novel backbone chemistry induces structural changes in the ionomer, restricting ionomer domain swelling under hydration while disrupting matrix crystallinity. These structural changes slightly reduce proton conductivity while significantly improving gas permeability. The performance implications of this tradeoff are assessed, which reveal the potential for substantial performance improvement by incorporation of highly permeable ionomers as the functional catalyst binder. These results underscore the significance of tailoring material chemistry to specific device requirements, where ionomer chemistry should be rationally designed to match the local transport requirements of the device architecture.

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Dynamic Emergence of Nanostructure and Transport Properties in Perfluorinated Sulfonic Acid Ionomers

10.26434/chemrxiv.12302693.v1 ◽

2020 ◽

Author(s):

Adlai Katzenberg ◽

Debdyuti Mukherjee ◽

Peter J. Dudenas ◽

Yoshiyuki Okamoto ◽

Ahmet Kusoglu ◽

...

Keyword(s):

Rate Constant ◽

Sulfonic Acid ◽

Mass Fraction ◽

Gas Permeability ◽

Transport Processes ◽

Segmental Mobility ◽

The Matrix ◽

Swelling Rate ◽

Ion Conducting ◽

Perfluorinated Sulfonic Acid

Limitations in fuel cell electrode performance have motivated the development of ion-conducting binders (ionomers) with high gas permeability. Such ionomers have been achieved by copolymerization of perfluorinated sulfonic acid (PFSA) monomers with bulky and asymmetric monomers, leading to a glassy ionomer matrix with chemical and mechanical properties that differ substantially from common PFSA ionomers (e.g., Nafion™). In this study, we use perfluorodioxolane-based ionomers to provide fundamental insights into the role of the matrix chemical structure on the dynamics of structural and transport processes in ion-conducting polymers. Through in-situ water uptake measurements, we demonstrate that ionomer water sorption kinetics depend strongly on the properties and mass fraction of the matrix. As the PFSA mass fraction was increased from 0.26 to 0.57, the Fickian swelling rate constant decreased from 0.8 s-1 to 0.2 s-1, while the relaxation rate constant increased from 3.1×10-3 s-1 to 4.0×10-3. The true swelling rate, in nm s-1, was determined by the chemical nature of the matrix; all dioxolane-containing materials exhibited swelling rates ~1.5 - 2 nm s-1 compared to ~3 nm s-1 for Nafion. Likewise, Nafion underwent relaxation at twice the rate of the fastest-relaxing dioxolane ionomer. Reduced swelling and relaxation kinetics are due to limited matrix segmental mobility of the dioxolane-containing ionomers. We demonstrate that changes in conductivity are strongly tied to the polymer relaxation, revealing the decoupled roles of initial swelling and relaxation on hydration, nanostructure, and ion transport in perfluorinated ionomers.

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Development and Application of a Sample Holder for In Situ Gaseous TEM Studies of Membrane Electrode Assemblies for Polymer Electrolyte Fuel Cells

Microscopy and Microanalysis ◽

10.1017/s143192761701248x ◽

2017 ◽

Vol 23 (5) ◽

pp. 945-950 ◽

Cited By ~ 2

Author(s):

Takeo Kamino ◽

Toshie Yaguchi ◽

Takahiro Shimizu

Keyword(s):

Fuel Cells ◽

Polymer Electrolyte ◽

Structural Changes ◽

Membrane Electrode Assembly ◽

Polymer Electrolyte Fuel Cells ◽

Polymer Electrolyte Fuel Cell ◽

Membrane Electrode ◽

Sample Holder ◽

Electrode Assemblies

AbstractPolymer electrolyte fuel cells hold great potential for stationary and mobile applications due to high power density and low operating temperature. However, the structural changes during electrochemical reactions are not well understood. In this article, we detail the development of the sample holder equipped with gas injectors and electric conductors and its application to a membrane electrode assembly of a polymer electrolyte fuel cell. Hydrogen and oxygen gases were simultaneously sprayed on the surfaces of the anode and cathode catalysts of the membrane electrode assembly sample, respectively, and observation of the structural changes in the catalysts were simultaneously carried out along with measurement of the generated voltages.

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Dynamic Emergence of Nanostructure and Transport Properties in Perfluorinated Sulfonic Acid Ionomers

10.26434/chemrxiv.12302693 ◽

2020 ◽

Author(s):

Adlai Katzenberg ◽

Debdyuti Mukherjee ◽

Peter J. Dudenas ◽

Yoshiyuki Okamoto ◽

Ahmet Kusoglu ◽

...

Keyword(s):

Rate Constant ◽

Sulfonic Acid ◽

Mass Fraction ◽

Gas Permeability ◽

Transport Processes ◽

Segmental Mobility ◽

The Matrix ◽

Swelling Rate ◽

Ion Conducting ◽

Perfluorinated Sulfonic Acid

Limitations in fuel cell electrode performance have motivated the development of ion-conducting binders (ionomers) with high gas permeability. Such ionomers have been achieved by copolymerization of perfluorinated sulfonic acid (PFSA) monomers with bulky and asymmetric monomers, leading to a glassy ionomer matrix with chemical and mechanical properties that differ substantially from common PFSA ionomers (e.g., Nafion™). In this study, we use perfluorodioxolane-based ionomers to provide fundamental insights into the role of the matrix chemical structure on the dynamics of structural and transport processes in ion-conducting polymers. Through in-situ water uptake measurements, we demonstrate that ionomer water sorption kinetics depend strongly on the properties and mass fraction of the matrix. As the PFSA mass fraction was increased from 0.26 to 0.57, the Fickian swelling rate constant decreased from 0.8 s-1 to 0.2 s-1, while the relaxation rate constant increased from 3.1×10-3 s-1 to 4.0×10-3. The true swelling rate, in nm s-1, was determined by the chemical nature of the matrix; all dioxolane-containing materials exhibited swelling rates ~1.5 - 2 nm s-1 compared to ~3 nm s-1 for Nafion. Likewise, Nafion underwent relaxation at twice the rate of the fastest-relaxing dioxolane ionomer. Reduced swelling and relaxation kinetics are due to limited matrix segmental mobility of the dioxolane-containing ionomers. We demonstrate that changes in conductivity are strongly tied to the polymer relaxation, revealing the decoupled roles of initial swelling and relaxation on hydration, nanostructure, and ion transport in perfluorinated ionomers.

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Synthesis of Lithium-ion Conducting Polymers Designed by Machine Learning-based Prediction and Screening

Chemistry Letters ◽

10.1246/cl.180847 ◽

2019 ◽

Vol 48 (2) ◽

pp. 130-132 ◽

Cited By ~ 9

Author(s):

Kan Hatakeyama-Sato ◽

Toshiki Tezuka ◽

Yoshinori Nishikitani ◽

Hiroyuki Nishide ◽

Kenichi Oyaizu

Keyword(s):

Machine Learning ◽

Conducting Polymers ◽

Lithium Ion ◽

Ion Conducting ◽

Ion Conducting Polymers

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Structure–Property Relationships in Single-Ion Conducting Multiblock Copolymers: A Phase Diagram and Ionic Conductivities

Macromolecules ◽

10.1021/acs.macromol.1c00493 ◽

2021 ◽

Author(s):

Jinseok Park ◽

Anne Staiger ◽

Stefan Mecking ◽

Karen I. Winey

Keyword(s):

Phase Diagram ◽

Ionic Conductivities ◽

Multiblock Copolymers ◽

Structure Property ◽

Structure Property Relationships ◽

Ion Conducting

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Thermo-Optical Properties of Perfluorinated Sulfonic Acid Membranes: An Investigation of Hydration Based on Absorption Spectra

Applied Spectroscopy ◽

10.1177/0003702817723649 ◽

2017 ◽

Vol 71 (11) ◽

pp. 2504-2511 ◽

Cited By ~ 1

Author(s):

Daniele T. Dias ◽

Guy Lopes ◽

Tales Ferreira ◽

Ivanir L. Oliveira ◽

Caroline D. Rosa

Keyword(s):

Sulfonic Acid ◽

Room Temperature ◽

Water Retention ◽

Structural Changes ◽

Optical Characterization ◽

Scanning Calorimetry ◽

Experimental Procedure ◽

Nafion Membranes ◽

Perfluorinated Sulfonic Acid

The Nafion membranes are widely used in electrochemical applications such as fuel cells, chlor-alkali cells, and actuators–sensors. In this work, the thermal-optical characterization of Nafion in acid form was performed by photoacoustic spectroscopy, thermogravimetry, and differential scanning calorimetry. In the experimental procedure three distinct hydration levels were considered: (1) pristine membrane (λ ≅ H2O/–SO3H ≅ 5.6); (2) swelling process (λ ≅ 17.4); and (3) drying at controlled room temperature after swelling process (λ ≅ 6.5). The discovered behaviors showed significant irreversible structural changes induced by water retention in the membrane. These structural changes depend on the water population present in the clusters and also affect the directional thermal diffusivity of the membrane irreversibly.

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Nanomaterials and structures for the fourth innovation of polymer electrolyte fuel cell

Journal of Materials Research ◽

10.1557/jmr.2010.0280 ◽

2010 ◽

Vol 25 (11) ◽

pp. 2063-2071 ◽

Cited By ~ 14

Author(s):

Chanho Pak ◽

Sangkyun Kang ◽

Yeong Suk Choi ◽

Hyuk Chang

Keyword(s):

Energy Conversion ◽

Polymer Electrolyte ◽

Supported Catalysts ◽

Clean Energy ◽

Polymer Electrolyte Fuel Cell ◽

Membrane Electrode ◽

Conductive Membranes ◽

Perfluorinated Membranes ◽

Efficiency Cost ◽

Energy Conversion Devices

Polymer electrolyte fuel cells (PEFCs) are drawing attention as energy conversion devices for next generations because of their highly efficient, environmentally benign, and portable features. In the last five decades, three distinguishable innovations were achieved in terms of proton conductive membranes and electrodes: introduction of perfluorinated membranes into PEFCs, adoption of ionomers for electrodes, and increased toughness of membranes by reinforced membranes. The efficiency, cost, and durability achieved from the past three innovations are still not enough to replace competing technologies such as combustion engines. In this review, the authors would elucidate the three different methods based on nanotechnology to overcome the limits: nanoporous carbon-supported catalysts, nanocomposite membranes, and nanostructured membrane electrode assemblies, which will bring the fourth innovation to PEFCs. With the innovation, PEFCs will fulfill the goals of being clean-energy conversion devices in the major applications of stationary, portable, and vehicle markets.

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