| 1. |
- Allushi, Andrit, et al.
(författare)
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Highly conductive hydroxide exchange membranes containing fluorene-units tethered with dual pairs of quaternary piperidinium cations
- 2021
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Ingår i: Journal of Membrane Science. - : Elsevier BV. - 0376-7388. ; 632
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Tidskriftsartikel (refereegranskat)abstract
- In the pursuit of anion exchange membranes (AEMs) with high alkaline stability and hydroxide conductivity, we have prepared and characterized a series of poly(fluorene alkylene)s in which each fluorene unit was functionalized with dual pairs of quaternary piperidinium cations on flexible alkyl spacer chains. First, ether-free precursor polymers were synthesized in superacid mediated polyhydroxyalkylations of 2,2,2-trifluoroacetophenone, 9,9-dimethyl-2,7-diphenyl-9H-fluorene, and different amounts of 2,7-dibromo-9,9-bis(6-bromohexyl)-fluorene to regulate the degree of bromoalkylation. Subsequently, the bromoalkyl side chains were utilized to introduce bis-piperidinium (bisPip) cations via Menshutkin reactions. These materials formed transparent and mechanically strong AEMs upon casting. At 80 °C, the hydroxide conductivity of bisPip AEMs reached 85 and 150 mS cm–1 at ion-exchange capacities (IECs) of 2.0 and 2.8 mequiv g–1, respectively. Moreover, the bisPip AEMs showed high alkaline stability with an ionic loss of merely 6% following immersion in 5 M aq. NaOH solution for a period of 168 h at IEC = 2.8 mequiv g–1. Under these conditions, 1H NMR data indicated that a β-hydrogen in an alkyl spacer chain was about 8 times more susceptible to attacks by hydroxide ions than a β-hydrogen in a piperidinium ring. In comparison, corresponding AEMs with fluorene units functionalized with monoPip cations (i.e., a single pair of piperidinium cations per fluorine unit) showed lower conductivity and alkaline stability under the same conditions, demonstrating the advantage of locally concentrating the cations in the polymer structure by employingbisPip side chains.
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| 2. |
- Kang, Na Rae, et al.
(författare)
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Durable and highly proton conducting poly(arylene perfluorophenylphosphonic acid) membranes
- 2021
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Ingår i: Journal of Membrane Science. - 0376-7388. ; 623
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Tidskriftsartikel (refereegranskat)abstract
- Phosphonated aromatic polymers show several important advantages as proton exchange membranes (PEMs), including high thermal and chemical stability. However, the conductivity needs to be significantly enhanced for most electrochemical applications. Here, we have prepared a series poly(p-terphenyl perfluoroalkylene)s functionalized with highly acidic perfluorophenylphosphonic acid by first carrying out triflic acid mediated polyhydroxylations of p-terphenyl, 2,2,2-trifluoroacetophenone and perfluoroacetophenone. Subsequently, the resulting polymers were quantitatively and selectively phosphonated in the para positions of the pendant perfluorophenyl units by employing an efficient Michaelis-Arbuzov reaction. X-ray scattering of proton exchange membranes (PEMs) based on the phosphonated polymers showed efficient ionic clustering with the interdomain distance depending on the acid content of the polymer. Although the water uptake and swelling was moderate (even at high temperature) the PEMs showed high proton conductivity, up to 111 mS cm-1 at 80 °C fully hydrated, and reaching 4 mS cm-1 at 50% RH at the same temperature. This may be ascribed to the distinct phase separation and high acidity of the polymers. The stability of the PEMs was excellent with thermal decomposition only above ~400 °C. Moreover, no change in weight, appearance or molecular structure was detected after 5 h immersion in Fenton’s reagent at 80 °C, demonstrating an excellent chemical resistance of the PEMs towards free-radical attack. The radical resistance of the present phosphonated PEMs was found to increase with the acid content, which is contrast to corresponding sulfonated PEMs. The combination of high thermochemical stability and high conductivity implies that the present materials are attractive for use as ionomers in catalyst layers and as PEMs in fuel cells and water electrolyzer applications.
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| 3. |
- Pan, Dong, et al.
(författare)
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Improving poly(arylene piperidinium) anion exchange membranes by monomer design
- 2022
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Ingår i: Journal of Materials Chemistry A. - 2050-7488. ; 10:31, s. 16478-16489
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Tidskriftsartikel (refereegranskat)abstract
- Energy conversion devices such as alkaline membrane fuel cells and water electrolyzers rely critically on durable anion exchange membranes (AEMs) with high hydroxide conductivity. In this context, poly(arylene piperidinium)s have emerged as one of the top candidate materials. Here, we report on the preparation and properties of poly(arylene alkylene piperidinium)s (PAAPs) with significantly higher alkaline stability than current state-of-the-art poly(arylene piperidinium)s derived from piperidone. A new piperidine trifluoromethyl ketone monomer (TFPip) was designed, synthesized and employed in superacid-mediated polyhydroxyalkylations with p- and m-terphenyl, biphenyl and fluorene, respectively. The pendant piperidine rings of the resulting polymers were then quaternized and cycloquaternized to form N,N-dimethylpiperidinium (DMP) and 6-azonia-spiro[5.5]undecane (ASU) cations, respectively. Polymers based on p- and m-terphenyl were cast into mechanically strong AEMs which reached OH- conductivities close to 80 and 180 mS cm-1 at 20 and 80 °C, respectively. The AEMs also displayed an excellent resistance against OH- attack. For example, AEMs carrying DMP cations showed a mere 14% ionic loss after storage in 5 M aq. NaOH at 90 °C during 20 days. In comparison, a corresponding benchmark poly(arylene piperidinium) AEM lost three times as many DMP cations (42%) under the same conditions. The results of the study demonstrate that the overall properties and alkaline stability of AEMs can be considerably improved by rational monomer design.
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| 4. |
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| 5. |
- Allushi, Andrit, et al.
(författare)
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Ether-free polyfluorenes tethered with quinuclidinium cations as hydroxide exchange membranes
- 2019
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Ingår i: Journal of Materials Chemistry A. - 2050-7488. ; 7:47, s. 27164-27174
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Tidskriftsartikel (refereegranskat)abstract
- We report on aryl ether-free 2,7-diphenylfluorene-based copolymers tethered with quinuclidinium (Qui) cations via hexyl spacers, prepared through superacid catalyzed Friedel Crafts polycondensation and quaternization reactions. The 2,7-diphenylfluorene monomers were prepared by Suzuki coupling and employed to increase polymer backbone stiffness. Corresponding copolymers and anion-exchange membranes (AEMs) tethered with piperidinium (Pip) and trimethylalkyl ammonium (TMA) cations were prepared as reference materials. At a given water content, the AEM functionalized with Qui cations was the most efficient hydroxide conductor and reached 100 mS cm-1 at 80 °C at an ion exchange capacity of 2.0 mequiv g-1. Moreover, this membrane showed the highest thermal and alkaline stability in the series. 1H NMR analysis of AEMs stored in 2 M aq. NaOH at 90 °C over 672 h revealed the complete absence of ring-opening β-elimination in the bicyclic cage-like Qui structure, and only ~1% β-elimination in the hexyl spacer. In contrast, the Pip cations were found to degrade via β-elimination in both the monocyclic ring structure and the hexyl spacer. Results on the Pip-modified AEM implied that a β-hydrogen in the linear alkyl spacer chain was approximately 4 times more vulnerable to elimination than a β-hydrogen in the 6-membered ring. In addition, all the cations degraded via substitution reactions to some degree, and the total loss of Qui, Pip and TMA cations over the period was estimated to 4, 12 and 9%, respectively. The overall findings demonstrate that the combination of aryl-ether free backbone polymers and Qui cations results in durable and high-performance AEMs suitable for use in alkaline electrochemical energy conversion and storage devices.
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| 7. |
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| 8. |
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| 9. |
- Kang, Na Rae, et al.
(författare)
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Polyaromatic perfluorophenylsulfonic acids with high radical resistance and proton conductivity
- 2019
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Ingår i: ACS Macro Letters. - : American Chemical Society (ACS). - 2161-1653. ; 8:10, s. 1247-1251
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Tidskriftsartikel (refereegranskat)abstract
- We report on the straightforward metal-free synthesis of poly(p-terphenyl perfluorophenylsulfonic acid)s by efficient superacid catalyzed Friedel–Crafts polycondensations of commercially available perfluoroacetophenone and p-terphenyl, followed by sulfonation of the pendant pentafluorophenyl groups via a selective and quantitative thiolation-oxidation procedure. The stiff and well-defined polymer structure with precisely sequenced and highly acidic units induces efficient ionic clustering, restricted water uptake and swelling, excellent resistance against radical attack and very high proton conductivity. At 120 °C the conductivity reaches 40 and 232 mS cm-1 at 50 and 90% relative humidity, respectively, which very closely matches the benchmark Nafion NR212 membrane. The properties are further tuned by copolymerizations. Overall, the results demonstrate that these materials possess a very attractive combination of characteristics for use as high-performance proton-exchange membranes for fuel cells and water electrolyzers.
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