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Title: Chemical Stability via Radical Decomposition Using Silicotungstic Acid Moieties for Polymer Electrolyte Fuel Cells

Abstract

Chemical degradation of perfluorinated sulfonic acid membranes, such as Nafion, via radical attack, represents one of the current challenges of fuel cell durability. Here we report on a recent breakthrough in chemical durability that has been achieved through using covalently attached heteropoly acid (HPA) moieties as both the proton conducting acid and the radical decomposition catalyst. Exceptional chemical durability is reported for a thin (25 um) film in an accelerated stress test that eventually had an open circuit voltage decay rate of 520 uV h -1, which was shown to be a result of the formation of an electrical short after thinning due to mechanical stresses. A mechanism is proposed using density functional theory in which the W atoms in the HPA reversibly change oxidation state from W(VI) to W(V) while decomposing radical species. Using rate constants found in the literature and realistic concentrations of scavenging species, it is hypothesized that the rate of radical decomposition can be >35x faster for HPA containing membranes than it is for Ce doped films. Furthermore, it is concluded that covalently tethered HPA should be considered as a next generation chemical stabilization strategy for polymer electrolyte fuel cells.

Authors:
 [1];  [1];  [2];  [2]; ORCiD logo [1]
  1. Colorado School of Mines, Golden, CO (United States)
  2. National Renewable Energy Lab. (NREL), Golden, CO (United States)
Publication Date:
Research Org.:
National Renewable Energy Lab. (NREL), Golden, CO (United States)
Sponsoring Org.:
USDOE Office of Energy Efficiency and Renewable Energy (EERE), Fuel Cell Technologies Office (EE-3F)
OSTI Identifier:
1482850
Alternate Identifier(s):
OSTI ID: 1492509
Report Number(s):
NREL/JA-5900-73180
Journal ID: ISSN 0013-4651
Grant/Contract Number:  
AC36-08GO28308; EE0006363
Resource Type:
Published Article
Journal Name:
Journal of the Electrochemical Society
Additional Journal Information:
Journal Volume: 165; Journal Issue: 14; Journal ID: ISSN 0013-4651
Publisher:
The Electrochemical Society
Country of Publication:
United States
Language:
English
Subject:
30 DIRECT ENERGY CONVERSION; fuel cells; PEM; fuel cell electrolyte membrane; radical deposition mechanism

Citation Formats

Motz, Andrew R., Kuo, Mei -Chen, Bender, Guido, Pivovar, Bryan S., and Herring, Andrew M. Chemical Stability via Radical Decomposition Using Silicotungstic Acid Moieties for Polymer Electrolyte Fuel Cells. United States: N. p., 2018. Web. doi:10.1149/2.1361814jes.
Motz, Andrew R., Kuo, Mei -Chen, Bender, Guido, Pivovar, Bryan S., & Herring, Andrew M. Chemical Stability via Radical Decomposition Using Silicotungstic Acid Moieties for Polymer Electrolyte Fuel Cells. United States. doi:10.1149/2.1361814jes.
Motz, Andrew R., Kuo, Mei -Chen, Bender, Guido, Pivovar, Bryan S., and Herring, Andrew M. Tue . "Chemical Stability via Radical Decomposition Using Silicotungstic Acid Moieties for Polymer Electrolyte Fuel Cells". United States. doi:10.1149/2.1361814jes.
@article{osti_1482850,
title = {Chemical Stability via Radical Decomposition Using Silicotungstic Acid Moieties for Polymer Electrolyte Fuel Cells},
author = {Motz, Andrew R. and Kuo, Mei -Chen and Bender, Guido and Pivovar, Bryan S. and Herring, Andrew M.},
abstractNote = {Chemical degradation of perfluorinated sulfonic acid membranes, such as Nafion, via radical attack, represents one of the current challenges of fuel cell durability. Here we report on a recent breakthrough in chemical durability that has been achieved through using covalently attached heteropoly acid (HPA) moieties as both the proton conducting acid and the radical decomposition catalyst. Exceptional chemical durability is reported for a thin (25 um) film in an accelerated stress test that eventually had an open circuit voltage decay rate of 520 uV h-1, which was shown to be a result of the formation of an electrical short after thinning due to mechanical stresses. A mechanism is proposed using density functional theory in which the W atoms in the HPA reversibly change oxidation state from W(VI) to W(V) while decomposing radical species. Using rate constants found in the literature and realistic concentrations of scavenging species, it is hypothesized that the rate of radical decomposition can be >35x faster for HPA containing membranes than it is for Ce doped films. Furthermore, it is concluded that covalently tethered HPA should be considered as a next generation chemical stabilization strategy for polymer electrolyte fuel cells.},
doi = {10.1149/2.1361814jes},
journal = {Journal of the Electrochemical Society},
number = 14,
volume = 165,
place = {United States},
year = {2018},
month = {11}
}

Journal Article:
Free Publicly Available Full Text
Publisher's Version of Record
DOI: 10.1149/2.1361814jes

Figures / Tables:

Figure 1 Figure 1: Structure of silicotungstic acid functionalized poly(vinylidene fluoride-co-hexafluoropropylene) (PolyHPA) reproduced with permission from the Royal Society of Chemistry from Ref. 26.

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