Robust Hydroxide Ion Conducting Poly(biphenyl alkylene)s for Alkaline Fuel Cell Membranes

Lee, Woo Hyung; Kim, Yu Seung; Bae, Chulsung

doi:10.1021/acsmacrolett.5b00375

Cited by 279 publications

(217 citation statements)

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“…Elimination of alkaline-labile aryl ether bonds has already produced promising anion exchange membranes for alkaline fuel cells. 23 Our results indicate that adoption of a parallel synthetic approach may be an attractive pathway toward low-cost, non-perfluorinated, ion exchange membranes for AORFBs.…”

Section: Resultsmentioning

confidence: 75%

Communication—Sulfonated Poly (ether ether ketone) as Cation Exchange Membrane for Alkaline Redox Flow Batteries

Porcellinis

Mecheri

D’Epifanio

et al. 2018

J. Electrochem. Soc.

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A sulfonated poly (ether ether ketone) (sPEEK) was tested as the separator in a full alkaline flow battery with 2,6-dihydroxyanthraquinone-ferro/ferricyanide, DHAQ-FeCy, redox couples. Cell performance was compared to that of an identical cell utilizing a perfluorosulfonic acid (PFSA) membrane. Replacement of the PFSA membrane with sPEEK resulted in a 10% power density increase, a 40% decrease in capacity loss per day and an 85-fold decrease in ferricyanide permeation. Though long-term stability of sPEEK in alkaline media requires improvement, these results highlight the potential to produce non-fluorinated membranes with better performance in organic redox flow batteries than the commercially available PFSAs. Aqueous organic redox flow batteries (AORFBs) constitute one of the most attractive alternatives to solve the storage problem associated with environmentally friendly, yet intermittent, power sources. 1,2-9Promising electrolyte compositions have been reported for AORFBs using commercially available cation exchange membranes (CEMs) as the electrode separator. The typical materials of choice for these membranes are perfluorinated sulfonic acids (PFSAs), such as Nafion. One barrier that hinders their widespread adoption is their relatively high cost.10 Replacement of PFSAs with a non-fluorinated membrane could reduce the cost of the films by a factor of 2.5 and facilitate the commercial implementation of AORFBs.11 Though inspiring new AORFBs operating at neutral pH have recently been reported, 8,[12][13][14] the majority of the systems developed to date require relatively harsh operation conditions (pH>13 or pH<0). These operating parameters limit the polymer chemistry choices that warrant further exploration. One promising starting point is the sulfonated version of poly ether ether ketone (sPEEK). This material has been previously tested as the CEM in fuel cells and vanadium redox flow batteries.15,16 Herein we compare the performance of a sPEEK membrane with a 50% degree of sulfonation with that of a commercially available perfluorinated alternative, Nafion NR212. The sPEEK membranes exhibited higher ionic conductivity, higher peak power density, lower capacity loss per cycle, and lower crossover of electroactive species than the PFSA membranes. Though the long-term stability of these nonfluorinated polymers needs to be improved, these results illustrate the potential for producing non-fluorinated membranes with comparable or better performance than the commercially available PFSAs, if the hydrolysis-prone heteroatoms are eliminated from the polymer backbone. ExperimentalThe procedures used for membrane preparation and characterization, as well as cell assembly and testing, are included in the supplemental information (SI). Results and DiscussionMembrane properties relevant for flow cell performance are presented in Table I. The higher conductivity observed for sPEEK is ascribable to its higher ion exchange capacity and higher water uptake. The water uptake differences between sPEEK and Nafion in their cor...

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Section: Resultsmentioning

confidence: 75%

Communication—Sulfonated Poly (ether ether ketone) as Cation Exchange Membrane for Alkaline Redox Flow Batteries

Porcellinis

Mecheri

D’Epifanio

et al. 2018

J. Electrochem. Soc.

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“…With the aim to prepare AEMs based on a backbone polymer without ether bridges, Lee et al prepared high‐molecular weight poly(biphenyl alkylene) via acid‐catalyzed Friedel–Crafts polycondensation of biphenyl and trifluoromethyl bromopentyl ketone, before attaching QA groups via the resulting pentyl spacers (Scheme j) . Despite the spacer configuration, SAXS measurements did not reveal any ionomer peaks for these materials.…”

Section: Aems Based On Cationic Polymers With Different Side Chain Comentioning

confidence: 99%

Configuring Anion‐Exchange Membranes for High Conductivity and Alkaline Stability by Using Cationic Polymers with Tailored Side Chains

Jannasch

Weiber

2016

Macro Chemistry & Physics

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Polymeric anion-exchange membranes (AEMs) are critical components for alkaline membrane fuel cells (AMFCs) which offer several attractive advantages including the use of platinumfree catalysts and a wide choice of fuel. The development of AMFCs and other electrochemical energy systems is currently severely limited by the lack of AEMs with suffi cient alkaline stability. Still, signifi cant advances have been made in recent years and one of the most promising approaches to emerge is the design and synthesis of cationic polymers with various side chain arrangements. Especially, synthetic strategies where the cationic ionexchange groups are placed on pendant alkyl spacer chains along the backbone seem to signifi cantly improve microphase separation, hydroxide ion conductivity, and alkaline stability in relation to standard AEMs with cations placed in benzylic positions directly on the backbone. This article reviews recent approaches to high-performance cationic membrane polymers involving different side chain designs, and discusses some possible future directions.

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“…27,28 Hibbs has for example synthesised polyphenylenes tethered with trimethylammonium ions via hexyl spacers and reported a significant increase in the alkaline stability compared to corresponding polymers with BTA groups. 34 The high alkaline stability of alkyl trimethylammonium cations has been rationalized by Pivovar et al who via density functional theory calculations showed that Hofmann elimination is the most harmful degradation route for the alkyl trimethylammonium cations. 27,28 Lee and co--workers prepared fluorene-based polymers with trimethylammonium ions attached via hexyl spacer chains and reported high OH − conductivity and excellent alkaline stability.…”

Section: Introductionmentioning

confidence: 99%

Alkali-stable and highly anion conducting poly(phenylene oxide)s carrying quaternary piperidinium cations

2016

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New durable and hydroxide ion conducting anion--exchange membranes (AEMs) are currently required in order to develop alkaline fuel cells into efficient and clean energy conversion devices. In the present work we have attached quaternary piperidinium (QPi) groups to poly(2,6--dimethyl--1,4--phenylene oxide)s (PPOs) via flexible alkyl spacer chains with the aim to prepare AEMs. The bromine atoms of bromoalkylated PPOs were displaced in Menshutkin reactions to attach one or two QPi groups, respectively, via heptyl spacers. The cationic polymers have excellent solubility in, e.g., methanol, dimethylsulfoxide and N--methyl--2--pyrrolidone at room temperature, and form tough and transparent membranes. AEMs with bis--QPi side chains efficiently form ionic clusters and show very high hydroxide ion conductivities, up to 69 and 186 mS cm --1 at 20 and 80 °C, respectively. The AEMs further have excellent alkaline stability, and 1 H NMR analysis show no degradation of the AEMs after storage in 1 M NaOH at 90 °C during 8 days. Thermogravimetry indicate decomposition only above 225 °C. The AEM properties were further tuned by controlled formation of bis--QPi crosslinks through an efficient reaction between bromoalkylated PPO and 4,4′--trimethylenebis(1--methylpiperidine) during a reactive membrane casting process. In conclusion, alkali--stable and highly conductive AEMs for alkaline fuel cells can be prepared by placing cycloaliphatic quaternary ammonium cations on flexible side chains and crosslinks. 15This opens up for many synthetic possibilities to target new high--performance PPO--based AEMs.By employing standard procedures to introduce the cationic groups, e.g., chloromethylation and subsequent reaction with trimethylamine, benzyl trimethylammonium (BTA) groups are usually formed directly on aromatic polymer backbones. Unfortunately, quaternary ammonium (QA) groups in benzylic positions have in most cases proven to be quite sensitive towards nucleophilic attack by OH − , and also seem to activate the cleavage of adjacent ether links in aromatic polymer backbones. 16--18 QA groups with long alkyl chain segments are generally sensitive to Hofmann β--eliminations.Recently however, β--protons have been found to be far less

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Robust Hydroxide Ion Conducting Poly(biphenyl alkylene)s for Alkaline Fuel Cell Membranes

Cited by 279 publications

References 20 publications

Communication—Sulfonated Poly (ether ether ketone) as Cation Exchange Membrane for Alkaline Redox Flow Batteries

Communication—Sulfonated Poly (ether ether ketone) as Cation Exchange Membrane for Alkaline Redox Flow Batteries

Configuring Anion‐Exchange Membranes for High Conductivity and Alkaline Stability by Using Cationic Polymers with Tailored Side Chains

Alkali-stable and highly anion conducting poly(phenylene oxide)s carrying quaternary piperidinium cations

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