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Title: Structurally Cross-Linked Composite Proton Exchange Membranes

Abstract

Composite proton exchange membranes (PEMs) with a thermally cross-linked polymer backbone for high-temperature fuel cell applications were fabricated by casting tetrahydrofuran solution mixtures of tetraethoxysilane, a functional silane, a proton conductor, a molecular cross-linker (MXL), and an ethylene-methylacrylate copolymer with glycidyl methacrylate groups (PMG). The proton conductors used were commercial Keggin-structured silicotungstic acid (H4SiW12O40-26H2O, W12-STA) and lacunary W10- and W11-STA. The 3D cross-linked membranes were dense with in-situ formed SiO2 nanoparticles and showed high thermal stability, high chemical resistance to the Fenton's reagent, and moderate mechanical strength and flexibility. The corresponding proton conductivity was affected by formulation, membrane quality, loading level of W12-STA, temperature, and relative humidity, and was in the 20-25 mS/cm range at 80 C/100%RH with proton diffusion coefficients of 2.5-3.5 x 10-6 cm/s peaked in the {approx}90-110 C range for PEMs having a loading level of W12-STA >150 wt% (ratio to the weight sum of PMG and MXL).

Authors:
; ; ; ; ; ; ;
Publication Date:
Research Org.:
National Renewable Energy Lab. (NREL), Golden, CO (United States)
Sponsoring Org.:
USDOE
OSTI Identifier:
939282
DOE Contract Number:
AC36-99-GO10337
Resource Type:
Journal Article
Resource Relation:
Journal Name: ECS Transactions; Journal Volume: 5; Journal Issue: 1, 2007
Country of Publication:
United States
Language:
English
Subject:
14 SOLAR ENERGY; 36 MATERIALS SCIENCE; CASTING; COPOLYMERS; DIFFUSION; FLEXIBILITY; FUNCTIONALS; HIGH-TEMPERATURE FUEL CELLS; HUMIDITY; MEMBRANES; METHACRYLATES; MIXTURES; POLYMERS; PROTONS; STABILITY; TETRAHYDROFURAN; Solar Energy - Photovoltaics

Citation Formats

Pern, J., Turner, J., Dec, S., Yan, Y., To, B., Lipfert, D., Meng, F., and Herring, A. M.. Structurally Cross-Linked Composite Proton Exchange Membranes. United States: N. p., 2007. Web. doi:10.1149/1.2728999.
Pern, J., Turner, J., Dec, S., Yan, Y., To, B., Lipfert, D., Meng, F., & Herring, A. M.. Structurally Cross-Linked Composite Proton Exchange Membranes. United States. doi:10.1149/1.2728999.
Pern, J., Turner, J., Dec, S., Yan, Y., To, B., Lipfert, D., Meng, F., and Herring, A. M.. Mon . "Structurally Cross-Linked Composite Proton Exchange Membranes". United States. doi:10.1149/1.2728999.
@article{osti_939282,
title = {Structurally Cross-Linked Composite Proton Exchange Membranes},
author = {Pern, J. and Turner, J. and Dec, S. and Yan, Y. and To, B. and Lipfert, D. and Meng, F. and Herring, A. M.},
abstractNote = {Composite proton exchange membranes (PEMs) with a thermally cross-linked polymer backbone for high-temperature fuel cell applications were fabricated by casting tetrahydrofuran solution mixtures of tetraethoxysilane, a functional silane, a proton conductor, a molecular cross-linker (MXL), and an ethylene-methylacrylate copolymer with glycidyl methacrylate groups (PMG). The proton conductors used were commercial Keggin-structured silicotungstic acid (H4SiW12O40-26H2O, W12-STA) and lacunary W10- and W11-STA. The 3D cross-linked membranes were dense with in-situ formed SiO2 nanoparticles and showed high thermal stability, high chemical resistance to the Fenton's reagent, and moderate mechanical strength and flexibility. The corresponding proton conductivity was affected by formulation, membrane quality, loading level of W12-STA, temperature, and relative humidity, and was in the 20-25 mS/cm range at 80 C/100%RH with proton diffusion coefficients of 2.5-3.5 x 10-6 cm/s peaked in the {approx}90-110 C range for PEMs having a loading level of W12-STA >150 wt% (ratio to the weight sum of PMG and MXL).},
doi = {10.1149/1.2728999},
journal = {ECS Transactions},
number = 1, 2007,
volume = 5,
place = {United States},
year = {Mon Jan 01 00:00:00 EST 2007},
month = {Mon Jan 01 00:00:00 EST 2007}
}
  • A series of differently cross-linked FEP-g-polystyrene proton exchange membranes has been synthesized by the preirradiation grafting method [FEP: poly(tetrafluoroethylene-co-hexafluoropropylene)]. Divinylbenzene (DVB) and/or triallyl cyanurate (TAC) were used as cross-linkers in the membranes. It was found that the physical properties of the membranes, such as water-uptake and specific resistance, are strongly influenced by the nature of the cross-linker. Generally it can be stated that DVB decreases water-uptake and increases specific resistance; on the other hand TAC increases swelling and decreases specific resistance to values as low as 5.0 {Omega} cm at 60 C. The membranes were tested in H{sub 2}/O{sub 2}more » fuel cells for stability and performance. It was found that thick (170 {micro}m) DVB cross-linked membranes showed stable operation for 1,400 h at temperatures up to 80 C. The highest power density in the fuel cell was found for the DVB and TAC double-cross-linked membrane; it exceeded the value of a cell with a Nafion{reg_sign} 117 membrane by more than 60%.« less
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  • A unique one-step cross-linking strategy that connects quaternary ammonium centers using Grubbs II-catalyzed olefin metathesis was developed. The cross-linked anion exchange membranes showed swelling ratios of less than 10% and hydroxide conductivities of 18 to 40 mS cm(- 1). Cross-linking improved the membranes' stability to hydroxide degradation compared to their non-cross-linked analogues.
  • Random copolymers of isoprene and 4-vinylbenzyl chloride (VBCl) with varying compositions were synthesized via nitroxide-mediated polymerization. Subsequent quaternization afforded solvent processable and cross-linkable ionomers with a wide range of ion exchange capacities (IECs). Solution cast membranes were thermally cross-linked to form anion exchange membranes. Cross-linking was achieved by taking advantage of the unsaturations on the polyisoprene backbone, without added cross-linkers. A strong correlation was found between water uptake and ion conductivity of the membranes: conductivities of the membranes with IECs beyond a critical value were found to be constant related to their high water absorption. Environmentally controlled small-angle X-ray scatteringmore » experiments revealed a correlation between the average distance between ionic clusters and the ion conductivity, indicating that a well-connected network of ion clusters is necessary for efficient ion conduction and high ion conductivity.« less