How the Morphology of Nafion-Based Membranes Affects Proton Transport.

Ernestino Lufrano,Cataldo Simari,Isabella Nicotera,Riccardo Narducci,Maria Luisa Di Vona

doi:10.3390/polym13030359

Ernestino Lufrano, Cataldo Simari + Show 3 more

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https://doi.org/10.3390/polym13030359

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Journal: Polymers	Publication Date: Jan 22, 2021
Citations: 19	License type: CC BY 4.0

Affiliation: University of Calabria, University of Rome Tor Vergata

Abstract

This work represents a systematic and in-depth study of how Nafion 1100 membrane preparation procedures affect both the morphology of the polymeric film and the proton transport properties of the electrolyte. The membrane preparation procedure has non-negligible consequences on the performance of the proton-exchange membrane fuel cells (PEMFC) that operate within a wide temperature range (up to 120 °C). A comparison between commercial membranes (Nafion 117 and Nafion 212) and Nafion membranes prepared by three different procedures, namely (a) Nafion-recast, (b) Nafion uncrystallized, and (c) Nafion 117-oriented, was conducted. Electrochemical Impedance Spectroscopy (EIS) and Pulsed-field gradient nuclear magnetic resonance (PFG-NMR) investigations indicated that an anisotropic morphology could be achieved when a Nafion 117 membrane was forced to expand between two fixed and nondeformable surfaces. This anisotropy increased from ~20% in the commercial membrane up to 106% in the pressed membrane, where the ionic clusters were averagely oriented (Nafion 117-oriented) parallel to the surface, leading to a strong directionality in proton transport. Among the membranes obtained by solution-cast, which generally exhibited isotropic proton transport behavior, the Nafion uncrystallized membrane showed the lowest water diffusion coefficients and conductivities, highlighting the correlation between low crystallinity and a more branched and tortuous structure of hydrophilic channels. Finally, the dynamic mechanical analysis (DMA) tests demonstrated the poor elastic modulus for both uncrystallized and oriented membranes, which should be avoided in high-temperature fuel cells.

Highlights

In recent years, researchers have taken an interest in the development of more sustainable energies, both from an economic and environmental point of view
To highlight any sort of anisotropy in the membrane morphology induced by the fabrication procedure, the various Nafion 1100 membranes were investigated by electrochemical impedance spectroscopy (EIS) by using two cell configurations, through-plane and inplane
This study extends our knowledge of the morphology of Nafion membranes from previous Ionomer nc Analysis (INCA) method results

Summary

Introduction

Researchers have taken an interest in the development of more sustainable energies, both from an economic and environmental point of view. When relative humidity (RH)-temperature conditions overcome certain critical values, (70–130 ◦C and 95–100% RH [7]), the membranes undergo some irreversible processes that induce a decrease in their through-plane proton conductivity [8]. In 2013, Alberti et al [26], and in 2018, Narducci et al [22], reported a thermal treatment assisted by DMSO to increase crystallinity, and proposed a method to avoid or limit low-conductivity phase formation. This method was extended in 2019 by Giancola et al [4] to Aquivion. A well-defined annealing temperature (Tann), between the glass transition and the melting temperature of the crystalline phase, was chosen for the treatments performed at different times in order to increase the mechanical stability [27]

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Conclusion