N-cyclic quaternary ammonium-functionalized anion exchange membrane with improved alkaline stability enabled by aryl-ether free polymer backbones for alkaline fuel cells

Wang, Xin; Sheng, Weibing; Shen, Yinghua; Liu, Lei; Dai, Sheng; Li, Nanwen

doi:10.1016/j.memsci.2019.05.059

Cited by 57 publications

(39 citation statements)

References 52 publications

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“… 13 Following a different pathway, Li et al first modified PS via chloromethylation and azidation reactions and then used a Cu(I)-assisted click reaction to attach alkyne-functional N -alicyclic piperidine-based cations to obtain PS samples with the corresponding cations coupled to the backbone via triazole rings ( Figure 1 c). 38 In this case, the piperidine-based cations were attached in the 4-position, which means that all of the β-hydrogens were located in the six-membered ring structure to impede degradation via Hofmann elimination. 8 1 H NMR analysis of a PS functionalized with N , N -dimethyl piperidinium cations revealed degradation by methyl substitution after storage in 1 M NaOH in CD 3 OD/D 2 O at 80 °C, and a corresponding sample with spirocyclic cations showed no degradation under the same conditions after 3000 h. 38 These are excellent results but the synthetic pathway is complex and requires multiple steps.…”

Section: Introductionmentioning

confidence: 99%

“… 38 In this case, the piperidine-based cations were attached in the 4-position, which means that all of the β-hydrogens were located in the six-membered ring structure to impede degradation via Hofmann elimination. 8 1 H NMR analysis of a PS functionalized with N , N -dimethyl piperidinium cations revealed degradation by methyl substitution after storage in 1 M NaOH in CD 3 OD/D 2 O at 80 °C, and a corresponding sample with spirocyclic cations showed no degradation under the same conditions after 3000 h. 38 These are excellent results but the synthetic pathway is complex and requires multiple steps.…”

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: 99%

Section: Introductionmentioning

confidence: 99%

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

2020

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“…Among them, the hydroxide conductivity of ASU-PPO-60 membrane only decreased by 3.3% after immersion in 1 mol L −1 NaOH/H 2 O at 80 °C for 720 h (Figure 2b). Wang et al [72] synthesized a series of aryl ether-free polystyrene AEMs (PS-DMP and PS-ASU) (Figure 2c) containing 4-ethynyl-1,1-dimethyl-piperidinium iodide (DMP) or 3-ethynyl-6-azaspiro [5.5] undecan-6-ium bromide (ASU) cations via "click chemistry." The PS-ASU membrane had no obvious structural degradation in strong alkaline solution at 80 °C even for 3000 h, showing high chemical stability.…”

Section: Cyclic and Spirocyclic Quaternary Ammonium Cations For Anion Exchange Membranesmentioning

confidence: 99%

Section: Modified Quaternary Phosphonium For Anion Exchange Membranesmentioning

confidence: 99%

Progress in High‐Performance Anion Exchange Membranes Based on the Design of Stable Cations for Alkaline Fuel Cells

Tao

Wang

Zhao

et al. 2021

Adv Materials Technologies

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Solid alkaline fuel cells with anion exchange membranes (AEMs) have drawn wide attention and have become an important focus in the field of renewable energy cells in recent years due to their high electrode activity, potential application of non‐precious metal catalysts, and relatively low requirements for fuel purity. AEM is the central component in solid alkaline fuel cells, and plays the role of conducting ions, blocking fuel crossover and providing catalyst support in fuel cells. Its performance directly affects the efficiency and service life of fuel cells. With some exceptions, the majority of AEMs have relatively low hydroxide conductivity and poor durability, which cannot meet the requirements of practical applications. The past decade has witnessed great progress in AEM designs and stability. Various kinds of AEMs with different cationic structures have been designed, and their properties and application in fuel cells are investigated. This review provides a comparative investigation and summary of highlights from the design of cationic structures for AEMs, including cyclic and spirocyclic quaternary ammonium cations, modified quaternary phosphonium, modified imidazoles, guanidinium, and metal cations. The authors’ perspective on the remaining challenges and directions of AEMs research for future development are also discussed.

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“…AEMs feature cationic groups (e.g., quaternary ammonium, imidazolium, phosphonium, piperidinium, quinuclidinium, and guanidinium) attached to a hydrocarbon polymer backbone as hydroxide ion carriers and exhibit low gas permeability, high hydroxide-ion conductivity, good mechanical properties, and high chemical stability/durability under alkaline conditions [ 14 , 15 , 16 , 17 , 18 , 19 ] In addition to AEMs, another important polymeric component of AEMFCs is the electrode ionomer, which is the core material of the membrane electrode assembly (MEA) and acts as a physical binder to uniformly disperse the catalyst and fix the catalyst layer and the AEM. Moreover, the ionomer also acts as a pathway for hydroxide ion transfer in the catalyst layers, and it exhibits properties that are sometimes very different from those of AEMs.…”

Section: Introductionmentioning

confidence: 99%

Polystyrene-Based Hydroxide-Ion-Conducting Ionomer: Binder Characteristics and Performance in Anion-Exchange Membrane Fuel Cells

et al. 2021

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Polystyrene-based polymers with variable molecular weights are prepared by radical polymerization of styrene. Polystyrene is grafted with bromo-alkyl chains of different lengths through Friedel–Crafts acylation and quaternized to afford a series of hydroxide-ion-conducting ionomers for the catalyst binder for the membrane electrode assembly in anion-exchange membrane fuel cells (AEMFCs). Structural analyses reveal that the molecular weight of the polystyrene backbone ranges from 10,000 to 63,000 g mol−1, while the ion exchange capacity of quaternary-ammonium-group-bearing ionomers ranges from 1.44 to 1.74 mmol g−1. The performance of AEMFCs constructed using the prepared electrode ionomers is affected by several ionomer properties, and a maximal power density of 407 mW cm−2 and a durability exceeding that of a reference cell with a commercially available ionomer are achieved under optimal conditions. Thus, the developed approach is concluded to be well suited for the fabrication of next-generation electrode ionomers for high-performance AEMFCs.

show abstract

N-cyclic quaternary ammonium-functionalized anion exchange membrane with improved alkaline stability enabled by aryl-ether free polymer backbones for alkaline fuel cells

Cited by 57 publications

References 52 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 in High‐Performance Anion Exchange Membranes Based on the Design of Stable Cations for Alkaline Fuel Cells

Polystyrene-Based Hydroxide-Ion-Conducting Ionomer: Binder Characteristics and Performance in Anion-Exchange Membrane Fuel Cells

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