Decomposition pathways of an alkaline fuel cell membrane material component via evolved gas analysis

Macomber, Clay S.; Boncella, James M.; Pivovar, Bryan S.; Rau, J.

doi:10.1007/s10973-007-8930-x

Cited by 91 publications

(84 citation statements)

References 12 publications

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“…A current limitation in interpreting these findings arises because we are uncertain which species may exist in the gas phase above the solution due to difficulties obtaining gaseous samples for analysis. 32 Further reaction of the initial products may also account for their absence in the GC-MS analysis. The balance of the species found in the organic phase consisted of (methoxymethyl)benzene and dibenzyl ether at very similar concentrations.…”

Section: Resultsmentioning

confidence: 99%

Hydroxide based Benzyltrimethylammonium Degradation: Quantification of Rates and Degradation Technique Development

Sturgeon

Macomber

Engtrakul

et al. 2015

J. Electrochem. Soc.

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Anion exchange membranes (AEMs) are of interest as hydroxide conducting polymer electrolytes in electrochemical devices like fuel cells and electrolyzers. AEMs require hydroxide stable covalently tetherable cations to ensure required conductivity. Benzyltrimethylammonium (BTMA) has been the covalently tetherable cation that has been most often employed in anion exchange membranes because it is reasonably basic, compact (limited number of atoms per charge), and easily/cheaply synthesized. Several reports exist that have investigated hydroxide stability of BTMA under specific conditions, but consistency within these reports and comparisons between them have not yet been made. While the hydroxide stability of BTMA has been believed to be a limitation for AEMs, this stability has not been thoroughly reported. We have found that several methods reported have inherent flaws in their findings due to the difficulty of performing degradation experiments at high temperature and high pH. In order to address these shortcomings, we have developed a reliable, standardized method of determining cation degradation under conditions similar/relevant to those expected in electrochemical devices. The experimental method has been employed to determine BTMA stabilities at varying cation concentrations and elevated temperatures, and has resulted in improved experimental accuracy and reproducibility. Alkaline membrane fuel cells (AMFCs) employing anion exchange membranes (AEMs) are of increasing interest in fuel cell research as they potentially enable the use of non-Pt fuel cell catalysts, a primary cost limitation of proton exchange membrane fuel cells.

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Section: Resultsmentioning

confidence: 99%

Hydroxide based Benzyltrimethylammonium Degradation: Quantification of Rates and Degradation Technique Development

Sturgeon

Macomber

Engtrakul

et al. 2015

J. Electrochem. Soc.

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“…Fuel cell performance with SEBS-based AEMs resulted in peak power densities of 300 mW/cm 2 at 70 • C. Anion exchange membranes (AEMs) are a promising technology for alkaline membrane fuel cells (AMFCs), 1-6 redox flow batteries (RFBs), 7-13 alkaline water electrolyzers (AWEs) [14][15][16] and reverse electrodialysis (RED) cells. 17,18 The AEMs commonly reported in peer reviewed papers mostly contain quaternary ammonium fixed cation groups, mainly in the form of benzyl trimethylammonium cations.14,19-40 However, it has been shown that quaternary ammonium-based AEMs are sensitive toward Hofmann elimination 20,41 and direct nucleophilic elimination reactions 42,43 that result in loss of ion exchange capacity (IEC) and ionic conductivity. To resolve the stability problem inherent to quaternary-ammonium-group-containing AEMs, several alternative cations, including imidazolium, 41,44,45 benzimidazolium, 3,45,46 guanidinium, 15,47,48 phosphonium 8,9,49 and metal cations 50,51 have been proposed and investigated.…”

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confidence: 99%

Anion Exchange Membranes Based on Polystyrene-Block-Poly(ethylene-ran-butylene)-Block-Polystyrene Triblock Copolymers: Cation Stability and Fuel Cell Performance

Wang

Parrondo

Ramani

2017

J. Electrochem. Soc.

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A series of polystyrene-block-poly(ethylene-ran-butylene)-block-polystyrene (SEBS)-based anion exchange membranes (AEMs) were synthesized via chloromethylation of SEBS followed by quaternization with trimethylamine (TMA). SEBS-based AEMs functionalized with TMA + cations exhibited a hydroxide ion conductivity of 136 mS/cm at 70 • C. This membrane exhibited a phaseseparated morphology with wide and interconnected ionic channels as observed by atomic force microscopy. Poly (phenylene oxide) (PPO)-based AEMs with quaternary benzyl-trimethylammonium (TMA + ) and quaternary benzyl-tris(2,4,6-trimethoxyphenyl) phosphonium (TTMPP + ) and PPO-based AEMs with hexyl pendant chains were also synthesized and evaluated as binders in AMFC electrodes. PPO-based AEMs functionalized with TTMPP + demonstrated the best ex situ alkaline stability, losing only 9% of their ion-exchange-capacity after 30 days in 1M KOH (at 60 • C). The best in situ stability was achieved by SEBS-based MEAs (as membrane and as binder in the electrodes); The peak power density dropped approx. 35% after holding the cell at a constant voltage of 0.55V for 12 hours. Fuel cell performance with SEBS-based AEMs resulted in peak power densities of 300 mW/cm 2 at 70 • C. Anion exchange membranes (AEMs) are a promising technology for alkaline membrane fuel cells (AMFCs), 1-6 redox flow batteries (RFBs), 7-13 alkaline water electrolyzers (AWEs) [14][15][16] and reverse electrodialysis (RED) cells. 17,18 The AEMs commonly reported in peer reviewed papers mostly contain quaternary ammonium fixed cation groups, mainly in the form of benzyl trimethylammonium cations.14,19-40 However, it has been shown that quaternary ammonium-based AEMs are sensitive toward Hofmann elimination 20,41 and direct nucleophilic elimination reactions 42,43 that result in loss of ion exchange capacity (IEC) and ionic conductivity. To resolve the stability problem inherent to quaternary-ammonium-group-containing AEMs, several alternative cations, including imidazolium, 41,44,45 benzimidazolium, 3,45,46 guanidinium, 15,47,48 phosphonium 8,9,49 and metal cations 50,51 have been proposed and investigated. Phosphonium-based AEMs were investigated by Gu et al. 52 Gu et al. attached benzyl-tris(2,4,6-trimethoxyphenyl) phosphonium (TTMPP + ) onto polysulfone backbone to make AEMs, and found them to be alkaline stable; There was no ionic conductivity fade after immersion in 1M KOH for 30 days at room temperature. The bulky phosphonium-based AEMs remained stable in alkali because of the steric hindrance effect that protects the core phosphorus atom and the α-carbons against hydroxide ion attack. There is no possibility of β-elimination reaction because of the lack of hydrogen atoms in β-carbons. However, very few researchers have investigated in situ stability of bulky phosphorus-based AEMs. It is essential to correlate the ex situ stability results obtained in immersion alkaline stability tests with in situ stability in a functional H 2 /O 2 fuel cell.Hibbs 53 has shown that poly(phenylene)-bas...

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“…One key concern for these systems is the stability of cations that are attached to the polymer backbone of the membrane and are susceptible to chemical attack and degradation by hydroxide. [6][7][8] Benzyltrimethyl ammonium (BTMA + ) cation has been the most commonly employed cation in AEMs and has been investigated extensively for its application in AMFC. [9][10][11][12][13][14][15][16] Previous experimental measurements had shown that the concentration of unsubstituted BTMA + cation decreased by ∼10% within 29 days in 5 mol/L NaOH at 80…”

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confidence: 99%

Hydroxide Degradation Pathways for Substituted Benzyltrimethyl Ammonium: A DFT Study

Long

Pivovar

2014

ECS Electrochemistry Letters

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Decomposition pathways of an alkaline fuel cell membrane material component via evolved gas analysis

Cited by 91 publications

References 12 publications

Hydroxide based Benzyltrimethylammonium Degradation: Quantification of Rates and Degradation Technique Development

Hydroxide based Benzyltrimethylammonium Degradation: Quantification of Rates and Degradation Technique Development

Anion Exchange Membranes Based on Polystyrene-Block-Poly(ethylene-ran-butylene)-Block-Polystyrene Triblock Copolymers: Cation Stability and Fuel Cell Performance

Hydroxide Degradation Pathways for Substituted Benzyltrimethyl Ammonium: A DFT Study

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