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Title: Advancements in Anion Exchange Membrane Cations

Abstract

Anion-exchange membrane fuel cells (AME-FCs) are of increasingly popular interest as they enable the use of non-Pt fuel cell catalysts, the primary cost limitation of proton exchange membrane fuel cells. Benzyltrimethyl ammonium (BTMA) is the standard cation that has historically been utilized as the hydroxide conductor in AEMs. Herein we approach AEMs from two directions. First and foremost we study the stability of several different cations in a hydroxide solution at elevated temperatures. We specifically targeted BTMA and methoxy and nitro substituted BTMA. We've also studied the effects of adding an akyl spacer units between the ammonium cation and the phenyl group. In the second approach we use computational studies to predict stable ammonium cations, which are then synthesized and tested for stability. Our unique method to study cation stability in caustic conditions at elevated temperatures utilizes Teflon Parr reactors suitable for use under various temperatures and cation concentrations. NMR analysis was used to determine remaining cation concentrations at specific time points with GCMS analysis verifying product distribution. We then compare the experimental results with calculated modeling stabilities. Our studies show that the electron donating methoxy groups slightly increase stability (compared to that of BTMA), while the electron withdrawing nitromore » groups greatly decrease stability in base. These results give insight into possible linking strategies to be employed when tethering a BTMA like ammonium cation to a polymeric backbone; thus synthesizing an anion exchange membrane.« less

Authors:
 [1];  [1];  [1];  [1]
  1. 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 Science (SC), Basic Energy Sciences (BES) (SC-22)
OSTI Identifier:
1233475
Report Number(s):
NREL/JA-5900-65579
Journal ID: ISSN 1938-5862
DOE Contract Number:
AC36-08GO28308
Resource Type:
Journal Article
Resource Relation:
Journal Name: ECS Transactions; Journal Volume: 69; Journal Issue: 17; Related Information: ECS Transactions
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; anion-exchange membrane fuel cells; AME-FC; proton exchange membrane fuel cells

Citation Formats

Sturgeon, Matthew R., Long, Hai, Park, Andrew M., and Pivovar, Bryan S.. Advancements in Anion Exchange Membrane Cations. United States: N. p., 2015. Web. doi:10.1149/06917.0377ecst.
Sturgeon, Matthew R., Long, Hai, Park, Andrew M., & Pivovar, Bryan S.. Advancements in Anion Exchange Membrane Cations. United States. doi:10.1149/06917.0377ecst.
Sturgeon, Matthew R., Long, Hai, Park, Andrew M., and Pivovar, Bryan S.. 2015. "Advancements in Anion Exchange Membrane Cations". United States. doi:10.1149/06917.0377ecst.
@article{osti_1233475,
title = {Advancements in Anion Exchange Membrane Cations},
author = {Sturgeon, Matthew R. and Long, Hai and Park, Andrew M. and Pivovar, Bryan S.},
abstractNote = {Anion-exchange membrane fuel cells (AME-FCs) are of increasingly popular interest as they enable the use of non-Pt fuel cell catalysts, the primary cost limitation of proton exchange membrane fuel cells. Benzyltrimethyl ammonium (BTMA) is the standard cation that has historically been utilized as the hydroxide conductor in AEMs. Herein we approach AEMs from two directions. First and foremost we study the stability of several different cations in a hydroxide solution at elevated temperatures. We specifically targeted BTMA and methoxy and nitro substituted BTMA. We've also studied the effects of adding an akyl spacer units between the ammonium cation and the phenyl group. In the second approach we use computational studies to predict stable ammonium cations, which are then synthesized and tested for stability. Our unique method to study cation stability in caustic conditions at elevated temperatures utilizes Teflon Parr reactors suitable for use under various temperatures and cation concentrations. NMR analysis was used to determine remaining cation concentrations at specific time points with GCMS analysis verifying product distribution. We then compare the experimental results with calculated modeling stabilities. Our studies show that the electron donating methoxy groups slightly increase stability (compared to that of BTMA), while the electron withdrawing nitro groups greatly decrease stability in base. These results give insight into possible linking strategies to be employed when tethering a BTMA like ammonium cation to a polymeric backbone; thus synthesizing an anion exchange membrane.},
doi = {10.1149/06917.0377ecst},
journal = {ECS Transactions},
number = 17,
volume = 69,
place = {United States},
year = 2015,
month =
}
  • The increased interest in the use of anion exchange membranes (AEMs) for applications in electrochemical devices has prompted significant efforts in designing materials with robust stability in alkaline media. Most reported AEMs suffer from polymer backbone degradation as well as cation functional group degradation. In this report, we provide comprehensive experimental investigations for the analysis of cation functional group stability under alkaline media. A silver oxide-mediated ion exchange method and an accelerated stability test in aqueous KOH solutions at elevated temperatures using a Parr reactor were used to evaluate a broad scope of quaternary ammonium (QA) cationic model compound structures,more » particularly focusing on alkyl-tethered cations. Additionally, byproduct analysis was employed to gain better understanding of degradation pathways and trends of alkaline stability. Experimental results under different conditions gave consistent trends in the order of cation stability of various QA small molecule model compounds. Overall, cations that are benzyl-substituted or that are near to electronegative atoms (such as oxygen) degrade faster in alkaline media in comparison to alkyl-tethered QAs. These comprehensive model compound stability studies provide valuable information regarding the relative stability of various cation structures and can help guide researchers towards designing new and promising candidates for AEM materials.« less
  • Two anion receptors enhance liquid-liquid anion exchange when added to quaternary alkylammonium chloride anion exchangers, but with a striking dependence upon the structure of the alkylammonium cation. Two anion receptors were investigated, meso-octamethylcalix[4]pyrrole (C4P) and the bisthiourea tweezer 1,1'-(propane-1,3-diyl)bis(3-(4-sec-butylphenyl)thiourea (BTU). C4P has the unique ability in its cone anion-binding conformation to accept an appropriately sized electropositive species in the resulting cup formed by its four electron-rich pyrrole groups, while BTU is not expected to be predisposed for a specific host-guest interaction with the quaternary ammonium cations. It was therefore hypothesized that synergism between C4P and methyltri(C8,10)alkylammonium chloride (Aliquat 336) wouldmore » be uniquely pronounced owing to insertion of the methyl group of the Aliquat cation into the C4P cup, and we present herein data supporting this expectation. While synergism is comparatively weak for both exchangers with the BTU receptor, synergism between C4P and Aliquat 336 is indeed so strong that anion exchange prefers chloride over more extractable nitrate and trifluoroacetate, effectively overcoming the ubiquitous Hofmeister bias. A thermochemical analysis of synergistic anion exchange has been provided for the first time, unraveling the observed selectivity behavior and resulting in the estimation of binding constants for C4P with the ion pairs of A336+ with Cl , Br , OAcF3 , NO3 , and I . The uniquely strong positive cooperativity between A336 and C4P underscores the advantage of a supramolecular approach in the design of synergistic anion exchange systems.« less
  • It is now well established that incubation of mitochondria at pH 8 or higher opens up an electrophoretic anion transport pathway in the inner membrane. It is not known, however, whether this transport process has any physiological relevance. In this communication we demonstrate that anion uniport can take place at physiological pH if the mitochondria are depleted of matrix divalent cations with A23187 and EDTA. Using the light-scattering technique we have quantitated the rates of uniport of a wide variety of anions. Inorganic anions such as Cl-, SO4(2-), and Fe(CN)6(4-) as well as physiologically important anions such as HCO/sub 3/-,more » Pi-, citrate, and malate are transported. Some anions, however, such as gluconate and glucuronate do not appear to be transported. On the basis of the finding that the rate of anion uniport assayed in ammonium salts exhibits a dramatic decline associated with loss of matrix K+ via K+/H+ antiport, we suggest that anion uniport is inhibited by matrix protons. Direct inhibition of anion uniport by protons in divalent cation-depleted mitochondria is demonstrated, and the apparent pK of the binding site is shown to be about 7.8. From these properties we tentatively conclude that anion uniport induced by divalent cation depletion and that induced by elevated pH are catalyzed by the same transport pathway, which is regulated by both matrix H+ and Mg2+.« less