Highly Stable N3-Substituted Imidazolium-Based Alkaline Anion Exchange Membranes: Experimental Studies and Theoretical Calculations

Gu, Fei; Dong, Huilong; Li, Youyong; Si, Zhihong; Yan, Feng

doi:10.1021/ma402334t

Cited by 153 publications

(150 citation statements)

References 75 publications

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“…Some of the alkyl-substituted 1,2-dimethylimidazolium cations (1,2-DMIms) have also been synthesized and evaluated in alkaline solution. [11] The alkaline stability of imidazolium cations observed in experiments (DMIIm…”

Section: Substituent Effect On Lumo Energymentioning

confidence: 99%

Improving the Alkaline Stability of Imidazolium Cations by Substitution

Dong¹,

Gu²,

Li³

et al. 2014

ChemPhysChem

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Imidazolium cations are promising candidates for preparing anion-exchange membranes because of their good alkaline stability. Substitution of imidazolium cations is an efficient way to improve their alkaline stability. By combining density functional theory calculations with experimental results, it is found that the LUMO energy correlates with the alkaline stability of imidazolium cations. The results indicate that alkyl groups are the most suitable substituents for the N3 position of imidazolium cations, and the LUMO energies of alkyl-substituted imidazolium cations depend on the electron-donating effect and the hyperconjugation effect. Comparing 1,2-dimethylimidazolium cations (1,2-DMIm+) and 1,3-dimethylimidazolium cations (1,3-DMIm+) with the same substituents reveals that the hyperconjugation effect is more significant in influencing the LUMO energy of 1,3-DMIms. This investigation reveals that LUMO energy is a helpful aid in predicting the alkaline stability of imidazolium cations.

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Section: Substituent Effect On Lumo Energymentioning

confidence: 99%

Improving the Alkaline Stability of Imidazolium Cations by Substitution

Dong¹,

Gu²,

Li³

et al. 2014

ChemPhysChem

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“…14, 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.…”

mentioning

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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“…• C. [17][18][19][20][21] However, the AEMs with excep- * Electrochemical Society Active Member. a Present address: Institute for Molecular Engineering, University of Chicago, Chicago, Illinois 60637, USA.…”

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confidence: 99%

Mechanically Stable Poly(arylene ether) Anion Exchange Membranes Prepared from Commercially Available Polymers for Alkaline Electrochemical Devices

Arges

Wang

Jung

et al. 2015

J. Electrochem. Soc.

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The alkaline stability of poly(arylene ether) backbones in anion exchange polymer electrolyte membranes (AEMs) derivatized with quaternary benzyl N, N-dimethylhexylammmonium (DMH + ) and trimethylammonium (TMA + ) cation groups were investigated in poly(2,6-dimethyl 1,4-phenylene) oxide (PPO) and Udel polysulfone (PSF) polymers. Previous studies have demonstrated that quaternary ammonium and phosphonium groups trigger backbone degradation in commercially available poly(arylene ether)-based AEMs, despite the base polymers being resilient to alkaline solutions. Herein, we demonstrate that the electron withdrawing or donating character in the poly(arylene ether) backbone ultimately decides whether or not the prepared AEMs will become brittle in alkaline media due to cation triggered backbone degradation. Mitigation of cation triggered backbone degradation was only achieved when electron withdrawing substituents (not including the cation), such as sulfone or bromine groups, were eliminated from the polymer backbone (or, alternately, when electron donating groups were present). Hence, PPO AEMs prepared through chloromethylation, as opposed to free radical bromination, were resistant to backbone hydrolysis in alkaline media because each cation-functionalized repeat unit had two electron donating methyl groups rather than a single methyl group. In summary, this paper presents some design rules for preparing mechanically stable poly(arylene ether) AEMs from low cost, commercially available polymers for alkaline electrochemical devices.

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Highly Stable N3-Substituted Imidazolium-Based Alkaline Anion Exchange Membranes: Experimental Studies and Theoretical Calculations

Cited by 153 publications

References 75 publications

Improving the Alkaline Stability of Imidazolium Cations by Substitution

Improving the Alkaline Stability of Imidazolium Cations by Substitution

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

Mechanically Stable Poly(arylene ether) Anion Exchange Membranes Prepared from Commercially Available Polymers for Alkaline Electrochemical Devices

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