Enhanced water transport in AEMs based on poly(styrene–ethylene–butylene–styrene) triblock copolymer for high fuel cell performance

Gao, Xudong; Yu, Hongmei; Qin, Bowen; Jia, Jia; Hao, Jinkai; Xie, Feng; Shao, Zhigang

doi:10.1039/c8py01618f

Cited by 57 publications

(36 citation statements)

References 51 publications

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“… 8 , 34 This severely limits the stability and usefulness of AEM-carrying BTMA cations and typically restricts the AEMFC operating conditions. Two unrelated studies on SEBS functionalized with BTMA reported 19 32 and 28% 33 reductions in IEC, respectively, after 71 and 31 days, respectively, in 1 M aq KOH at 60 °C. Separation of the cation from the benzylic position has proven beneficial both in studies of model compounds 8 , 9 and in AEMs.…”

Section: Introductionmentioning

confidence: 98%

“… 21 − 24 Polystyrene (PS) is another example of an ether-free polymer that has been extensively investigated for the preparation of AEMs in the form of block and graft copolymers. 25 − 33 Varcoe et al have investigated the radiation grafting of poly(vinylbenzyl chloride) onto thin films of ethylene-tetrafluoroethylene (ETFE) 26 , 27 and low-density polyethylene (LDPE), 28 followed by quaternization with trimethylamine. Recently, fuel cell tests of such AEMs achieved >2 W cm –2 , which is one of the highest power densities reported for an AEMFC to date.…”

Section: Introductionmentioning

confidence: 99%

“… 28 Moreover, in a number of studies, the PS blocks of PS–poly(ethylene- co -butylene)–PS (SEBS) triblock copolymers have been chloromethylated and then quaternized using trimethylamine. 29 − 33 In both these approaches, the quaternization results in the formation of benzyltrimethyl ammonium (BTMA) cations ( Figure 1 a), which are highly activated for degradation by nucleophilic substitution at the benzylic position and may also degrade via anion-induced 1,4-elimination. 8 , 34 This severely limits the stability and usefulness of AEM-carrying BTMA cations and typically restricts the AEMFC operating conditions.…”

Section: Introductionmentioning

confidence: 99%

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Functionalizing Polystyrene with N-Alicyclic Piperidine-Based Cations via Friedel–Crafts Alkylation for Highly Alkali-Stable Anion-Exchange Membranes

2020

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Different anion-exchange membranes (AEMs) based on polystyrene (PS)-carrying benzyltrimethyl ammonium cations are currently being developed for use in alkaline fuel cells and water electrolyzers. However, the stability in relation to these state-of-the-art cations needs to be further improved. Here, we introduce highly alkali-stable mono- and spirocyclic piperidine-based cations onto PS by first performing a superacid-mediated Friedel–Crafts alkylation using 2-(piperidine-4-yl)propane-2-ol. This is followed by quaternization of the piperidine rings either using iodomethane to produce N , N -dimethyl piperidinium cations or by cyclo-quaternizations using 1,5-dibromopentane and 1,4-dibromobutane, respectively, to obtain N -spirocyclic quaternary ammonium cations. Thus, it is possible to functionalize up to 27% of the styrene units with piperidine rings and subsequently achieve complete quaternization. The synthetic approach ensures that all of the sensitive β-hydrogens of the cations are present in ring structures to provide high stability. AEMs based on these polymers show high alkaline stability and less than 5% ionic loss was observed by 1 H NMR spectroscopy after 30 days in 2 M aq NaOH at 90 °C. AEMs functionalized with N , N -dimethyl piperidinium cations show higher stability than the ones carrying N -spirocyclic quaternary ammonium. Careful analysis of the latter revealed that the rings formed in the cyclo-quaternization are more prone to degrade via Hofmann elimination than the rings introduced in the Friedel–Crafts reaction. AEMs with an ion-exchange capacity of 1.5 mequiv g –1 reach a hydroxide conductivity of 106 mS cm –1 at 80 °C under fully hydrated conditions. The AEMs are further tuned and improved by blending with polybenzimidazole (PBI). For example, an AEM containing 2 wt % PBI shows reduced water uptake and much improved robustness during handling and reaches 71 mS cm –1 at 80 °C. The study demonstrates that the critical alkaline stability of PS-containing AEMs can be significantly enhanced by replacing the benchmark benzyltrimethyl ammonium cations with N -alicyclic piperidine-based cations.

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Section: Introductionmentioning

confidence: 98%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Functionalizing Polystyrene with N-Alicyclic Piperidine-Based Cations via Friedel–Crafts Alkylation for Highly Alkali-Stable Anion-Exchange Membranes

2020

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“…Raising their IEC is an efficient and simple way to improve the conductivity of AEMs. Unfortunately, membrane swelling is generally accompanied with high IEC and thus results in poor mechanical strength of AEMs (Pan et al, 2012;Lu et al, 2013;Hou et al, 2016;Shukala and Shahi, 2018;Gao et al, 2019a). The swelling ratio of AEMs could be greatly reduced by introducing cross-linked structures, while the tight structure of membranes hinder the mobility of OH − , which reduces their conductivity (Liang et al, 2019;Lin et al, 2019b).…”

Section: Hydroxide Conductivitymentioning

confidence: 99%

Progress of Alkaline Anion Exchange Membranes for Fuel Cells: The Effects of Micro-Phase Separation

Lin

2020

Front. Mater.

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Compared with that of proton exchange membrane fuel cells (PEMFCs), alkaline anion exchange membrane fuel cells (AEMFCs) with alkaline anion exchange membranes (AEMs) as electrolytes are attracting increased attention due to their potential use as non-precious catalysts. As one of the key components of AEMFCs, an ideal AEM must possess high hydroxide conductivity, good thermal stability, sufficient mechanical stability, and excellent long-term durability at elevated temperatures in an alkaline environment. Until now, a large number of AEMs with various chemical structures and properties have been prepared, and studied in detail, and it has been found that the microphase separation structure greatly affected the performance of AEMs. This minireview provides recent progress made of AEMs with hydrophilic/hydrophobic microphase separation structure. The hydroxide conductivity, alkaline stability, and mechanical properties of AEMs could be improved due to the formation of hydrophilic/hydrophobic microphase separation in the membranes. The relationship among the microphase separation, the chemical structure of the polymers, and the performance of membranes has been discussed in detail. This article attempts to give an overview of some key factors for the future design of novel AEMs with excellent performance such as high conductivity and improved chemical stability.

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“…Diffusion resistance of AEMs can also be tuned by controlling the hydrophilicity of the AEMs. X. Gao, et al characterized water transport properties of poly (styrene-ethylene-butylene-styrene) based AEM as function of temperature and RH[137]. It was found that the water permeation flux through the AEM increased with temperature following the Fick's law of diffusion and was proportional to the water content gradient and diffusion coefficient.…”

mentioning

confidence: 99%

A comprehensive review on water management strategies and developments in anion exchange membrane fuel cells

Rambabu

Turtayeva

et al. 2020

International Journal of Hydrogen Energy

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In spite of significant achievements in alkaline exchange membrane fuel cells (AEMFCs) in recent years, they are still lagging behind proton exchange membrane fuel cells (PEMFCs) due to performance instability. Among the relevant operational parameters of AEMFC, the researchers have found that poor water management within the cell was the main reason for failure of the system. In the past five years, numerous modeling and experimental works were reported proposing different strategies to improve water management of AEMFC. The achievable power output in AEMFCs is then comparable with that of PEMFCs or even more. Efforts have to be continued, but AEMFCs can become a strong competitor in the market place. This review paper discusses the strategies and developments impacting water management of AEMFCs providing knowledge source for upcoming studies.

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Enhanced water transport in AEMs based on poly(styrene–ethylene–butylene–styrene) triblock copolymer for high fuel cell performance

Abstract: Anion exchange membrane fuel cells (AEMFCs) have received a considerable amount of attention in the past decades as a lower cost alternative to proton exchange membrane fuel cells (PEMFCs).

Cited by 57 publications

References 51 publications

Functionalizing Polystyrene with N-Alicyclic Piperidine-Based Cations via Friedel–Crafts Alkylation for Highly Alkali-Stable Anion-Exchange Membranes

Functionalizing Polystyrene with N-Alicyclic Piperidine-Based Cations via Friedel–Crafts Alkylation for Highly Alkali-Stable Anion-Exchange Membranes

Progress of Alkaline Anion Exchange Membranes for Fuel Cells: The Effects of Micro-Phase Separation

A comprehensive review on water management strategies and developments in anion exchange membrane fuel cells

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