<i>N</i>-Alkyl Interstitial Spacers and Terminal Pendants Influence the Alkaline Stability of Tetraalkylammonium Cations for Anion Exchange Membrane Fuel Cells

Nuñez, Sean A.; Capparelli, Clara; Hickner, Michael A.

doi:10.1021/acs.chemmater.5b04767

Cited by 120 publications

(81 citation statements)

References 51 publications

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“…Recent studies have shown that cyclic ammonium (24)(25)(26)(27) and tetraalkyl ammonium cations, specifically those with long alkyl chains (18)(19)(20)(28)(29)(30), have better alkaline stability than traditional benzyltrimethyl ammonium cations (31)(32)(33). Other cations, such as imidazolium (16,21,(34)(35)(36)(37)(38)(39)(40)(41)(42)(43), phosphonium (44)(45)(46)(47)(48)(49), and metal cations (50)(51)(52)(53)(54), have also been widely applied in various AAEMs.…”

Section: Significancementioning

confidence: 99%

Highly conductive and chemically stable alkaline anion exchange membranes via ROMP of trans -cyclooctene derivatives

You

Padgett

MacMillan

et al. 2019

Proc. Natl. Acad. Sci. U.S.A.

134

107

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Alkaline anion exchange membranes (AAEMs) are an important component of alkaline exchange membrane fuel cells (AEMFCs), which facilitate the efficient conversion of fuels to electricity using nonplatinum electrode catalysts. However, low hydroxide conductivity and poor long-term alkaline stability of AAEMs are the major limitations for the widespread application of AEMFCs. In this paper, we report the synthesis of highly conductive and chemically stable AAEMs from the living polymerization of trans-cyclooctenes. A trans-cyclooctene-fused imidazolium monomer was designed and synthesized on gram scale. Using these highly ring-strained monomers, we produced a range of block and random copolymers. Surprisingly, AAEMs made from the random copolymer exhibited much higher conductivities than their block copolymer analogs. Investigation by transmission electron microscopy showed that the block copolymers had a disordered microphase segregation which likely impeded ion conduction. A cross-linked random copolymer demonstrated a high level of hydroxide conductivity (134 mS/cm at 80°C). More importantly, the membranes exhibited excellent chemical stability due to the incorporation of highly alkaline-stable multisubstituted imidazolium cations. No chemical degradation was detected by 1 H NMR spectroscopy when the polymers were treated with 2 M KOH in CD 3 OH at 80°C for 30 d.alkaline anion exchange membrane | trans-cyclooctene | block and random copolymer | cross-linked polymer | transmission electron microscopy A lkaline anion exchange membranes (AAEMs) are a class of polymer electrolytes constructed from immobilized cations with hydroxide counteranions (1-3). AAEMs have been widely used for a variety of electrochemical applications, such as redox flow batteries, electrodialysis, and water electrolysis (4-7). One of the most important applications for AAEMs is their use as polyelectrolytes in alkaline exchange membrane fuel cells (AEMFCs). These devices can efficiently convert chemical energy in fuels (e.g., H 2 , hydrazine, and direct alcohols) into electricity. In comparison with proton exchange membrane fuel cells and aqueous alkaline fuel cells, AEMFCs are advantageous because they allow for rapid reduction of oxygen at the cathode, limit fuel cross-over, prevent the formation of carbonate precipitates, and are compatible with nonnoble electrocatalysts (8-12). Because of their essential role in AEMFCs, AAEMs have been extensively studied to optimize their performance and, in particular, to improve their hydroxide conductivity and alkaline stability.Hydroxide conductivity is one of the most important parameters used to evaluate AAEMs, because it is directly related to the ohmic resistance and power density of an AEMFC (9). There are several strategies to enhance the hydroxide conductivity of AAEMs. The most straightforward method is to increase the ion exchange capacity (IEC), such that more ions are present in AAEMs. However, a higher IEC typically results in higher water uptake. While the presence of water facilitates h...

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Section: Significancementioning

confidence: 99%

Highly conductive and chemically stable alkaline anion exchange membranes via ROMP of trans -cyclooctene derivatives

You

Padgett

MacMillan

et al. 2019

Proc. Natl. Acad. Sci. U.S.A.

134

107

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“…[31][32][33][34][35] The technique would be equally applicable at different humidity,p otential, and temperature conditions. Equivalent AEMs (without DBPF) in either chloride or hydroxide forms were assembled in an AEM fuel cell and tested under conditions identical to those used in the in situ fluorescenceexperiments.…”

Section: In Situ Fluorescence Spectroscopy Experimentsmentioning

confidence: 99%

“…These conditions allowed the measurement of the rate of degradation at the most stringent conditions (OCV) reported by severala u- thors. [31][32][33][34][35] The technique would be equally applicable at different humidity,p otential, and temperature conditions. The resulting IEC and hydroxide ionic conductivity values are shown in Figures 6and 7.…”

Section: In Situ Fluorescence Spectroscopy Experimentsmentioning

confidence: 99%

Detection of Reactive Oxygen Species in Anion Exchange Membrane Fuel Cells using In Situ Fluorescence Spectroscopy

et al. 2017

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The objectives of this study were: 1) to confirm superoxide anion radical (O ) formation, and 2) to monitor in real time the rate of O generation in an operating anion exchange membrane (AEM) fuel cell using in situ fluorescence spectroscopy. 1,3-Diphenlisobenzofuran (DPBF) was used as the fluorescent molecular probe owing to its selectivity and sensitivity toward O in alkaline media. The activation energy for the in situ generation of O during AEM fuel cell operation was estimated to be 18.3 kJ mol . The rate of in situ generation of O correlated well with the experimentally measured loss in AEM ion-exchange capacity and ionic conductivity attributable to oxidative degradation.

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“…The chemical and mechanical durability of AEMs are determined by the polymer main chains, functional cationic groups, and the arrangement of tether structures . In the past decade, there have been a variety of polymers with aromatic main backbone chains such as poly(phenylene oxide), poly(arylene ethers), poly(sulfone)s, and others, being used as AEM materials .…”

Section: Introductionmentioning

confidence: 99%

High Performance Anion Exchange Membrane Fuel Cells Enabled by Fluoropoly(olefin) Membranes

Zhu

Peng

Shang

et al. 2019

Adv Funct Materials

Self Cite

147

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Although the peak power density of anion exchange membrane fuel cells (AEMFCs) has been raised from ≈0.1 to ≈1.4 W cm −2 over the last decade, a majority of AEMFCs reported in the literature have not been demonstrated to achieve consistently high performance and steady-state operation. Poly(olefin)-based AEMs with fluorine substitution on the aromatic comonomer show considerably higher dimensional stability compared to samples that do not contain fluorine. More importantly, fluorinated poly(olefin)-based AEMs exhibit high hydroxide conductivity without excessive hydration due to a new proposed mechanism where the fluorinated dipolar monomer facilitates increased hydroxide dissociation and transport. Using this new generation of AEMs, a stable, high-performance AEMFC is operated for 120 h. When the fuel cell configuration is subjected to a constant current density of 600 mA cm −2 under H 2 /O 2 flow, the cell voltage declines only 11% (from 0.75 to 0.67 V) for the first 20 h during break-in and the cell voltage loss is low (0.2 mV h −1 ) over the subsequent 100 h of cell testing. The ease of synthesis, potential for low-cost commercialization, and remarkable ex situ properties and in situ performance of fluoropoly(olefin)-based AEM renders this material a benchmark membrane for practical AEMFC applications.

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N-Alkyl Interstitial Spacers and Terminal Pendants Influence the Alkaline Stability of Tetraalkylammonium Cations for Anion Exchange Membrane Fuel Cells

Cited by 120 publications

References 51 publications

Highly conductive and chemically stable alkaline anion exchange membranes via ROMP of trans -cyclooctene derivatives

Highly conductive and chemically stable alkaline anion exchange membranes via ROMP of trans -cyclooctene derivatives

Detection of Reactive Oxygen Species in Anion Exchange Membrane Fuel Cells using In Situ Fluorescence Spectroscopy

High Performance Anion Exchange Membrane Fuel Cells Enabled by Fluoropoly(olefin) Membranes

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