Recent advancements of covalent organic frameworks (COFs) as proton conductors under anhydrous conditions for fuel cell applications

Joseph, Vellaichamy; Nagai, Atsushi

doi:10.1039/d3ra04855a

Cited by 4 publications

(2 citation statements)

References 78 publications

(89 reference statements)

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“…For anhydrous conduction, porous materials, including MOF, CMP, and POM, have been investigated by using inorganic or organic molecules as proton carriers. − These porous materials exhibit proton conductivities of up to 8.2 × 10 –2 S cm –1 . We have demonstrated that stable COFs are robust enough to enable anhydrous proton conduction. − …”

Section: Introductionmentioning

confidence: 99%

Exceptional Anhydrous Proton Conduction in Covalent Organic Frameworks

Tao,

Jiang

2024

J. Am. Chem. Soc.

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Covalent organic frameworks (COFs) offer an irreplaceable platform for mass transport, as they provide aligned onedimensional channels as pathways. Especially, proton conduction is of great scientific interest and technological importance. However, unlike proton conduction under humidity, anhydrous proton conduction remains a challenge, as it requires robust materials and proceeds under harsh conditions. Here, we report exceptional anhydrous proton conduction in stable crystalline porous COFs by integrating neat phosphoric acid into the channels to form extended hydrogen-bonding networks. The phosphoric acid networks in the pores are stabilized by hierarchical multipoint and multichain hydrogen-bonding interactions with the 3D channel walls. We synthesized five hexagonal COFs that possess different pore sizes, which are gradually tuned from micropores to mesopores. Remarkably, mesoporous COFs with a high pore volume exhibit an exceptional anhydrous proton conductivity of 0.31 S cm −1 , which marks the highest conductivity among all examples reported for COFs. We observed that the proton conductivity is dependent on the pore volume, pore size, and content of phosphoric acid. Increasing the pore volume improves the proton conductivity in an exponential fashion. Remarkably, changing the pore volume from 0.41 to 1.60 cm 3 g −1 increases the proton conductivity by 1150-fold. Interestingly, as the pore size increases, the activation energy barrier of proton conduction decreases in linear mode. The mesopores enable fast proton hopping across the channels, while the micropores follow sluggish vehicle conduction. Experiments on tuning phosphoric acid loading contents revealed that a well-developed hydrogen-bonding phosphoric acid network in the pores is critical for proton conduction.

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Section: Introductionmentioning

confidence: 99%

Exceptional Anhydrous Proton Conduction in Covalent Organic Frameworks

Tao,

Jiang

2024

J. Am. Chem. Soc.

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“…Therefore, the development of high-performance PEM hold great significance for enhancing performance, reducing costs and industrializing PEMFC. Numerous studies have been conducted on the manufacturing process and material modification of PEM using organic polymers with sulfonic groups, , metal–organic frameworks (MOFs) or coordination polymers (CPs), − carbon organic frameworks, , graphene derivatives and their composition materials . Among these materials, crystalline MOFs/CPs and HOFs have attracted increasing attention due to their tunable framework structure, chemical stability, and crystallizability, which can provide an opportunity to explore the relationship between structure and property in terms of proton conduction. − However, the grain boundaries resistance and brittleness of crystalline materials limit proton transfer and membrane formation thus hindering practical application.…”

Section: Introductionmentioning

confidence: 99%

Comparative Study on the Proton Conduction Behaviors of Two Acidic Amphiphilic and Hydrophilic Coordination Compounds in Nafion Composite Membranes

Zou,

Huan,

Wang

et al. 2024

Inorg. Chem.

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The acidic amphiphilic compound H[Co(H 2 L1)(HL1)(phen)]•3H 2 O (H 4 (Co-L1), H 3 L1 = 5-(3′, 5′-dicarboxylphenyl)-pyridine-2-carboxylic, phen = phenanthroline) and the hydrophilic compound [Ni(HL2)(H 2 O) 5 ]•H 2 O (H(Ni-L2), H 3 L2 = 5-(3′,5′-dicarboxylphenyl)-pyridine-3-carboxylic) were synthesized via hydrothermal reactions at acidic conditions. The acidity of H 4 (Co-L1) is stronger than of H(Ni-L2); while the hydrogen bond continuity in H 4 (Co-L1) extended monodirectionally, which is smaller compared to the three-directional extension observed in H(Ni-L2). The proton conduction behaviors of these two compounds as fillers of Nafion composite membranes have been investigated. The results indicate that the optimal doping amounts of H 4 (Co-L1) and H(Ni-L2) are 2 and 1%, respectively; the proton conductivities of H 4 (Co-L1)/Nafion-2 and H(Ni-L2)/Nafion-1 composite membranes are 0.243 and 0.212 S•cm −1 , respectively, which are approximately 50.2 and 30.6% higher than that of pure Nafion membrane, respectively. A higher doping amount of H 4 (Co-L1) can be attributed to its hydrophobic phen ligand, which promotes compatibility with Nafion membrane and reduces aggregation. Hydrogen bond continuity has a more significant effect on proton conductivity than acidity at relatively low doping amounts; conversely, this relationship reverses at relatively high doping amounts.

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