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Title: Cerium Ion Mobility and Diffusivity Rates in Perfluorosulfonic Acid Membranes Measured via Hydrogen Pump Operation

Abstract

Ion mobility and diffusivity coefficients were determined for cerium ions in Nafion XL perfluorosulfonic acid ionomer membranes at 100% and 50% relative humidity in a conductivity cell using a hydrogen pump. We quantified Ce ion migration profiles as a function of charge transfer through the cell using X-ray fluorescence (XRF). To decouple simultaneous effects of Ce ion mobility and back-diffusion which occur due to potential and concentration gradients, respectively, a one-dimensional model was developed and fit to these intermittent XRF profiles. The resulting mobility and diffusivity coefficients demonstrate the dramatic effects of potential and concentration gradients on Ce ion migration during PEM fuel cell operation.

Authors:
ORCiD logo [1]; ORCiD logo [2]; ORCiD logo [2];  [3];  [3]; ORCiD logo [2]; ORCiD logo [2]
  1. Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Univ. of Delaware, Newark, DE (United States)
  2. Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
  3. Univ. of Delaware, Newark, DE (United States)
Publication Date:
Research Org.:
Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
Sponsoring Org.:
USDOE Office of Energy Efficiency and Renewable Energy (EERE). Fuel Cell Technologies Program (EE-3F)
OSTI Identifier:
1407921
Report Number(s):
LA-UR-17-28795
Journal ID: ISSN 0013-4651
Grant/Contract Number:
AC52-06NA25396
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
Journal of the Electrochemical Society
Additional Journal Information:
Journal Volume: 164; Journal Issue: 12; Journal ID: ISSN 0013-4651
Publisher:
The Electrochemical Society
Country of Publication:
United States
Language:
English
Subject:
25 ENERGY STORAGE; 37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; Energy Sciences; fuel cells, cation, diffusivity, migration, durability

Citation Formats

Baker, Andrew M., Babu, Siddharth Komini, Mukundan, Rangachary, Advani, Suresh G., Prasad, Ajay K., Spernjak, Dusan, and Borup, Rod L. Cerium Ion Mobility and Diffusivity Rates in Perfluorosulfonic Acid Membranes Measured via Hydrogen Pump Operation. United States: N. p., 2017. Web. doi:10.1149/2.1221712jes.
Baker, Andrew M., Babu, Siddharth Komini, Mukundan, Rangachary, Advani, Suresh G., Prasad, Ajay K., Spernjak, Dusan, & Borup, Rod L. Cerium Ion Mobility and Diffusivity Rates in Perfluorosulfonic Acid Membranes Measured via Hydrogen Pump Operation. United States. doi:10.1149/2.1221712jes.
Baker, Andrew M., Babu, Siddharth Komini, Mukundan, Rangachary, Advani, Suresh G., Prasad, Ajay K., Spernjak, Dusan, and Borup, Rod L. 2017. "Cerium Ion Mobility and Diffusivity Rates in Perfluorosulfonic Acid Membranes Measured via Hydrogen Pump Operation". United States. doi:10.1149/2.1221712jes. https://www.osti.gov/servlets/purl/1407921.
@article{osti_1407921,
title = {Cerium Ion Mobility and Diffusivity Rates in Perfluorosulfonic Acid Membranes Measured via Hydrogen Pump Operation},
author = {Baker, Andrew M. and Babu, Siddharth Komini and Mukundan, Rangachary and Advani, Suresh G. and Prasad, Ajay K. and Spernjak, Dusan and Borup, Rod L.},
abstractNote = {Ion mobility and diffusivity coefficients were determined for cerium ions in Nafion XL perfluorosulfonic acid ionomer membranes at 100% and 50% relative humidity in a conductivity cell using a hydrogen pump. We quantified Ce ion migration profiles as a function of charge transfer through the cell using X-ray fluorescence (XRF). To decouple simultaneous effects of Ce ion mobility and back-diffusion which occur due to potential and concentration gradients, respectively, a one-dimensional model was developed and fit to these intermittent XRF profiles. The resulting mobility and diffusivity coefficients demonstrate the dramatic effects of potential and concentration gradients on Ce ion migration during PEM fuel cell operation.},
doi = {10.1149/2.1221712jes},
journal = {Journal of the Electrochemical Society},
number = 12,
volume = 164,
place = {United States},
year = 2017,
month = 9
}

Journal Article:
Free Publicly Available Full Text
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  • Perfluorosulfonic acid membranes, the polymer of choice for polymer electrolyte hydrogen fuel cells, are susceptible to degradation due to attacks on polymer chains from radicals. Mitigation of this attack by cerium-based radical scavengers is an approach that has shown promise. In this work, two formulations of single-crystal cerium oxide nanoparticles, with an order of magnitude difference in particle size, are incorporated into said membranes and subjected to proton conductivity measurements and ex-situ durability tests. We found that ceria is reduced to Ce(III) ions in the acidic environment of a heated, humidified membrane which negatively impacts proton conductivity. In liquid andmore » gas Fenton testing, fluoride emission is reduced by an order of magnitude, drastically increasing membrane longevity. Side-product analysis demonstrated that in the liquid Fenton test, the main point of attack are weak polymer end groups, while in the gas Fenton test, there is additional side-chain attack. Both mechanisms are mitigated by the addition of the ceria nanoparticles, whereby the extent of the durability improvement is found to be independent of particle size.« less
  • A radiotracer technique is developed to obtain simultaneously the concentration of all mobile species within a perfluorinated ion-exchange membrane, the most promising membrane material available fuel cells. The ion concentrations are correlated accurately by a theoretical model that incorporates the alignment of solvent dipoles and hydration of mobile ions. The results of the equilibrium analysis include membrane partition coefficients, which are required for the description of ion and solvent transport within ion-exchange membranes.
  • A two-parameter equation describing water vapor uptake in perfluorosulfonic acid membranes is derived based on the Flory-Huggins model combined with a chemical equilibrium constant for proton transfer. Temperature-dependent expressions for the proton-transfer equilibrium constant K(T) = 0.0256 {times} exp[(22.4 kJ/mol)/RT] and the Flory interaction parameter {chi}(T) = 1.936 {minus} (2.18 kJ/mol)/RT are discussed. Advantages of the new equation include accurate reduction of activity vs. water vapor uptake data for perfluorosulfonic acid membranes with few parameters and a well-behaved dependence of activity on composition and temperature. Comparisons of model results with water uptake measurements in the literature are given. An explanationmore » for the difference in water uptake by membranes in contact with liquid water and with saturated vapor is proposed based on an interpretation of the temperature dependence of water uptake.« less
  • We present a detailed analysis of the nanostructure of short side chain (SSC) perfluorosulfonic acid membrane and its effect on H{sub 2}O network percolation, H{sub 3}O{sup +} and H{sub 2}O diffusion, and mean residence times of H{sub 3}O{sup +} and H{sub 2}O near SO{sub 3}{sup -} groups based on molecular dynamics simulations. We studied a range of hydration levels ({lambda}) at temperatures of 300 and 360 K, and compare the results to our previous findings in the benchmark Nafion membrane at 300 K. The water channel diameter is about 20% larger in Nafion, while the extent of SO3- clustering ismore » more in SSC membrane. The calculated channel diameter is in excellent agreement with the recently proposed cylindrical water channel model of these membranes. The H{sub 2}O network percolation occurs at comparable hydration levels, and the diffusion coefficients of H{sub 2}O and H{sub 3}O{sup +} are similar in SSC and Nafion membranes. Raising the temperature of the SSC membrane from 300 to 360 K provides a much bigger increase in proton vehicular diffusion coefficient (by a factor of about 4) than changing the side chain length. H3O+ ions are found to exchange more frequently with SO{sub 3}{sup -} partners at the higher temperature. Our key findings are that (a) the hydrophobic-hydrophilic separation in the two membranes is surprisingly similar; (b) at all hydration levels studied, the longer side chain of Nafion is bent and is effectively equivalent to a short side chain in terms of extension into the water domain; and (c) proton transport along the centre of the channel is improbable and vehicular proton transport occurs between SO{sub 3}{sup -} groups. The simulations are validated by good agreement with corresponding experimental values for the simulated membrane density and diffusion coefficients of H{sub 2}O.« less