Crystallinity Enhancement of Nafion Electrolyte Membranes Assisted by a Molecular Gelator

Publication: Research - peer-reviewJournal article – Annual report year: 2012

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Crystallinity Enhancement of Nafion Electrolyte Membranes Assisted by a Molecular Gelator. / Zhang, Wenjing; Yue, Po-Lock; Gao, Ping.

In: Langmuir, Vol. 27, No. 15, 2011, p. 9520-9527.

Publication: Research - peer-reviewJournal article – Annual report year: 2012

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Zhang, Wenjing; Yue, Po-Lock; Gao, Ping / Crystallinity Enhancement of Nafion Electrolyte Membranes Assisted by a Molecular Gelator.

In: Langmuir, Vol. 27, No. 15, 2011, p. 9520-9527.

Publication: Research - peer-reviewJournal article – Annual report year: 2012

Bibtex

@article{d1b05cffeefe45739d1ebb32842d4a7d,
title = "Crystallinity Enhancement of Nafion Electrolyte Membranes Assisted by a Molecular Gelator",
publisher = "American Chemical Society",
author = "Wenjing Zhang and Po-Lock Yue and Ping Gao",
year = "2011",
doi = "10.1021/la201047k",
volume = "27",
number = "15",
pages = "9520--9527",
journal = "Langmuir",
issn = "0743-7463",

}

RIS

TY - JOUR

T1 - Crystallinity Enhancement of Nafion Electrolyte Membranes Assisted by a Molecular Gelator

A1 - Zhang,Wenjing

A1 - Yue,Po-Lock

A1 - Gao,Ping

AU - Zhang,Wenjing

AU - Yue,Po-Lock

AU - Gao,Ping

PB - American Chemical Society

PY - 2011

Y1 - 2011

N2 - Nanocrystallites, acting as physical cross-links in Nafion membranes, play a crucial role in building blocks for improving mechanical durability and stopping fuel crossover. However, Nafion membranes suffer from low crystallinity due to the irregular pendent side chains, which hinder self-aggregation of the poly(tetrafluoroethylene) (PTFE) backbones. For the first time, a molecular gelator was introduced in the membrane casting process to enhance the rate of self-assembly of PTFE backbones so as to increase the membrane’s crystallinity as well as proton conductivity without sacrificing the purity of Nafion. The molecular gelator used was 3,4-dimethylbenzaldehyde (DMBA). Addition of 0.5 wt % DMBA led to a 42% increase in crystallinity, a 32% increase in yield strength, a 22% increase in tensile modulus and an 18% increase in proton conductivity at 60 °C and 90% relative humidity. Additionally, the membrane electrode assembly (MEA) prepared from the membranes cast from the solution containing 0.5 wt % DMBA also showed an increase of 17% in maximum power density in comparison to the MEA prepared from pure Nafion membrane in a single cell polarization test without any external humidification. Transmission electron microscopy (TEM) and molecular dynamics simulation were used to elucidate the structural changes in Nafion membrane due to the introduction of DMBA. It was observed that the presence of DMBA gives wider crystalline regions under TEM. The molecular dynamics simulation at 500 K shows that the PTFE backbones become elongated in the presence of DMBA due to the enhanced mobility. This is consistent with the observed increase in crystallinity in the membrane as it means reduced entropic change upon crystallization.

AB - Nanocrystallites, acting as physical cross-links in Nafion membranes, play a crucial role in building blocks for improving mechanical durability and stopping fuel crossover. However, Nafion membranes suffer from low crystallinity due to the irregular pendent side chains, which hinder self-aggregation of the poly(tetrafluoroethylene) (PTFE) backbones. For the first time, a molecular gelator was introduced in the membrane casting process to enhance the rate of self-assembly of PTFE backbones so as to increase the membrane’s crystallinity as well as proton conductivity without sacrificing the purity of Nafion. The molecular gelator used was 3,4-dimethylbenzaldehyde (DMBA). Addition of 0.5 wt % DMBA led to a 42% increase in crystallinity, a 32% increase in yield strength, a 22% increase in tensile modulus and an 18% increase in proton conductivity at 60 °C and 90% relative humidity. Additionally, the membrane electrode assembly (MEA) prepared from the membranes cast from the solution containing 0.5 wt % DMBA also showed an increase of 17% in maximum power density in comparison to the MEA prepared from pure Nafion membrane in a single cell polarization test without any external humidification. Transmission electron microscopy (TEM) and molecular dynamics simulation were used to elucidate the structural changes in Nafion membrane due to the introduction of DMBA. It was observed that the presence of DMBA gives wider crystalline regions under TEM. The molecular dynamics simulation at 500 K shows that the PTFE backbones become elongated in the presence of DMBA due to the enhanced mobility. This is consistent with the observed increase in crystallinity in the membrane as it means reduced entropic change upon crystallization.

U2 - 10.1021/la201047k

DO - 10.1021/la201047k

JO - Langmuir

JF - Langmuir

SN - 0743-7463

IS - 15

VL - 27

SP - 9520

EP - 9527

ER -