As a new class of crystalline porous organic materials, covalent organic frameworks (COFs) have attracted considerable attention for proton conduction owing to their regular channels and tailored ...functionality. However, most COFs are insoluble and unprocessable, which makes membrane preparation for practical use a challenge. In this study, we used surface‐initiated condensation polymerization of a trialdehyde and a phenylenediamine for the synthesis of sulfonic COF (SCOF) coatings. The COF layer thickness could be finely tuned from 10 to 100 nm by controlling the polymerization time. Moreover, free‐standing COF membranes were obtained by sacrificing the bridging layer without any decomposition of the COF structure. Benefiting from the abundant sulfonic acid groups in the COF channels, the proton conductivity of the SCOF membrane reached 0.54 S cm−1 at 80 °C in pure water. To our knowledge, this is one of the highest values for a pristine COF membrane in the absence of additional additives.
A free‐standing covalent organic framework (COF) membrane with controlled thickness was obtained by using a surface‐initiated polymerization strategy (see picture). The rigid organic skeleton and defined pore structure of the COF membrane as well as the abundance of sulfonic acid groups throughout the layer led to superior proton conductivity of 0.54 S cm−1 at 80 °C in pure water.
Mimicking proton conduction mechanism of Nafion to construct novel proton-conducting materials with low cost and high proton conductivity is of wide interest. Herein, we have designed and synthesized ...a cationic covalent organic framework with high thermal and chemical stability by combining a cationic monomer, ethidium bromide (EB) (3,8-diamino-5-ethyl-6-phenylphenanthridinium bromide), with 1,3,5-triformylphloroglucinol (TFP) in Schiff base reactions. This is the first time that the stable cationic crystalline frameworks allowed for the fabrication of a series of charged COFs (EB-COF:X, X = F, Cl, Br, I) through ion exchange processes. Exchange of the extra framework ions can finely modulate the COFs’ porosity and pore sizes at nanoscale. More importantly, by introducing PW12O40 3– into this porous cationic framework, we can greatly enhance the proton conductivity of ionic COF-based material. To the best of our knowledge, EB-COF:PW 12 shows the best proton conductivity at room temperature among ever reported porous organic materials.
Porous aromatic frameworks (PAFs) show promising potential in anionic conduction due to their high stability and customizable functionality. However, the insolubility of most PAFs presents a ...significant challenge in their processing into membranes and subsequent applications. In this study, continuous PAF membranes with adjustable thickness were successfully created using liquid‐solid interfacial polymerization. The rigid backbone and the stable C−C coupling endow PAF membrane with superior chemical and dimensional stabilities over most conventional polymer membranes. Different quaternary ammonium functionalities were anchored to the backbone through flexible alkyl chains with tunable length. The optimal PAF membrane exhibited an OH− conductivity of 356.6 mS ⋅ cm−1 at 80 °C and 98 % relative humidity. Additionally, the PAF membrane exhibited outstanding alkaline stability, retaining 95 % of its OH− conductivity after 1000 hours in 1 M NaOH. To the best of our knowledge, this is the first application of PAF materials in anion exchange membranes, achieving the highest OH− conductivity and exceptional chemical/dimensional stability. This work provides the possibility for the potential of PAF materials in anionic conductive membranes.
A series of ultrathin free‐standing porous aromatic framework (PAF) membranes were prepared by liquid‐solid interfacial polymerization, and applied in the anion conduction for the first time, with excellent performance in hydroxide conductivity and stability due to the rational presence of transporting sites and rigid structure of PAF.
Efficient construction of proton transport channels in proton exchange membranes maintaining conductivity under varied humidity is critical for the development of fuel cells. Covalent organic ...frameworks (COFs) hold great potential in providing precise and fast ion transport channels. However, the preparation of continuous free‐standing COF membranes retaining their inherent structural advantages to realize excellent proton conduction performance is a major challenge. Herein, a zwitterionic COF material bearing positive ammonium ions and negative sulphonic acid ions is developed. Free‐standing COF membrane with adjustable thickness is constructed via surface‐initiated polymerization of COF monomers. The porosity, continuity, and stability of the membranes are demonstrated via the transmission electron microscopy (TEM), atomic force microscopy (AFM), and scanning electron microscopy (SEM) characterization. The rigidity of the COF structure avoids swelling in aqueous solution, which improves the chemical stability of the proton exchange membranes and improves the performance stability. In the higher humidity range (50–90%), the prepared zwitterionic COF membrane exhibits superior capability in retaining the conductivity compared to COF membrane merely bearing sulphonic acid group. The established strategy shows the potential for the application of zwitterionic COF in the proton exchange membrane fuel cells.
Free‐standing covalent organic framework (COF) membranes with controlled thickness and zwitterions are successfully prepared by surface‐initiated polymerization and ring‐opening reactions. The well crystallinity and the rigid backbone endow the zwitterionic COF membrane with continuous transport channels and non‐swelling character, thus make the COF membrane with high proton conductivity and excellent water retention capability.
Electrocatalytic nitrogen reduction reaction (NRR) under ambient conditions provides an intriguing pathway to convert N2 into NH3. However, significant kinetic barriers of the NRR at low temperatures ...in desirable aqueous electrolytes remain a grand challenge due to the inert N≡N bond of the N2 molecule. Herein, we propose a unique strategy for in situ oxygen vacancy construction to address the significant trade‐off between N2 adsorption and NH3 desorption by building a hollow shell structured Fe3C/Fe3O4 heterojunction coated with carbon frameworks (Fe3C/Fe3O4@C). In the heterostructure, the Fe3C triggers the oxygen vacancies of the Fe3O4 component, which are likely active sites for the NRR. The design could optimize the adsorption strength of the N2 and NxHy intermediates, thus boosting the catalytic activity for the NRR. This work highlights the significance of the interaction between defect and interface engineering for regulating electrocatalytic properties of heterostructured catalysts for the challenging NRR. It could motivate an in‐depth exploration to advance N2 reduction to ammonia.
We report an effective and feasible strategy to engineer oxygen vacancies in situ by constructing a heterojunction of Fe3C/Fe3O4 that enables an “optimized activation‐desorption” system for the electrochemical conversion of N2 into NH3. Combined with experimental results and DFT calculations, the synergistic effect between oxygen vacancies and heterojunction was further elucidated.
A new cationic triazole‐based metal–organic framework encapsulating Keggin‐type polyoxometalates, with the molecular formula Co(BBPTZ)3HPMo12O40⋅24 H2O compound 1; ...BBPTZ=4,4′‐bis(1,2,4‐triazol‐1‐ylmethyl)biphenyl is hydrothermally synthesized and characterized by elemental analysis, IR spectroscopy, thermogravimetric analysis, powder X‐ray diffraction, and single‐crystal X‐ray diffraction. The structure of compound 1 contains a non‐interpenetrated 3D CdSO4 (cds)‐type framework with two types of channels that are interconnected with each other; straight channels that are occupied by the Keggin‐type POM anions, and wavelike channels that contain lattice water molecules. The catalytic activity of compound 1 in the oxidative desulfurization reaction indicates that it is not only an effective and size‐selective heterogeneous catalyst, but it also exhibits distinct structural stability in the catalytic reaction system.
Sulfur no more: A cationic triazole‐based metal–organic framework encapsulating Keggin‐type polyoxometalates, with the molecular formula Co(BBPTZ)3HPMo12O40⋅24 H2O BBPTZ=4,4′‐bis(1,2,4‐triazol‐1‐ylmethyl)biphenyl, is synthesized, characterized and shown to be active in oxidative desulfurization catalysis. POM=polyoxometalate; MOF=metal–organic framework; cds=CdSO4.
Polyoxometalates (POMs) are considered as promising catalysts with unique redox activity at the molecular level for energy storage. However, eco‐friendly iron‐oxo clusters with special metal ...coordination structures have rarely been reported for Li‐ion storage. Herein, three novel redox‐active tetranuclear iron‐oxo clusters have been synthesized using the solvothermal method with different ratios of Fe3+ and SO42−. Further, they can serve as anode materials for Li‐ion batteries. Among them, cluster H6Fe4O2(H2O)2(SO4)7⋅H2O, the stable structure extended by SO42− with a unique 1D pore, displays a specific discharge capacity of 1784 mAh g−1 at 0.2 C and good cycle performance (at 0.2 C and 4 C). This is the first instance of inorganic iron‐oxo clusters being used for Li‐ion storage. Our findings present a new molecular model system with a well‐defined structure and offer new design concepts for the practical application of studying the multi‐electron redox activity of iron‐oxo clusters.
Iron‐oxo molecular clusters constructed from sulfate and iron ions with unique redox activity show porous structures and can be used as excellent anode materials for Li‐ion batteries.
Proton exchange membrane fuel cells are still limited as state-of-art proton exchange membranes perform poorly at high and low temperature and are easily damaged by harsh electrochemical conditions ...such as reactive peroxide species. One effective solution to this issue is to develop new types of proton conductive materials that are capable of working in a broad temperature range. A simple vacuum-assisted filtration method is employed to obtain a well-ordered new proton-conducting membrane by immobilizing nanosized bismuth oxide clusters H
Bi
O
(NO
)
·6(H
O) {H
Bi
O
} onto graphene oxide (GO) supports (named as {H
Bi
O
}/GO). {H
Bi
O
}/GO is stable in acidic media and has high proton conductivity over the temperature range from -40 to 80 °C. The proton conductivity of the {H
Bi
O
}/GO membrane is 0.564 S cm
at 80 °C in aqueous solution (in plane), and 0.1 S cm
at 80 °C and 97% RH (out of plane), respectively. Without loss of high proton conductivity, the membrane also exhibited 100-fold lower methanol permeability than a Nafion 117 membrane. Moreover, {H
Bi
O
}/GO displayed good catalytic decomposition of hydrogen peroxide and superior humidity response and recovery properties. These advantages mean that {H
Bi
O
}/GO holds great promise as a solid-state electrolyte that can potentially be applied in energy conversion devices in the future.
Multifunctional flexible electronics present tremendous opportunities in the rapidly evolving digital age. One potential avenue to realize this goal is the integration of polyoxometalates (POMs) and ...ionic liquid‐based gels (ILGs), but the challenge of macrophase separation due to poor compatibility, especially caused by repulsion between like‐charged units, poses a significant hurdle. Herein, the possibilities of producing diverse and homogenous POMs‐containing ionohydrogels by nanoconfining POMs and ionic liquids (ILs) within an elastomer‐like polyzwitterionic hydrogel using a simple one‐step random copolymerization method, are expanded vastly. The incorporation of polyzwitterions provides a nanoconfined microenvironment and effectively modulates excessive electrostatic interactions in POMs/ILs/H2O blending system, facilitating a phase transition from macrophase separation to a submillimeter scale worm‐like microphase‐separation system. Moreover, combining POMs‐reinforced ionohydrogels with a developed integrated self‐powered sensing system utilizing strain sensors and Zn‐ion hybrid supercapacitors has enabled efficient energy storage and detection of external strain changes with high precision. This work not only provides guidelines for manipulating morphology within phase‐separation gelation systems, but also paves the way for developing versatile POMs‐based ionohydrogels for state‐of‐the‐art smart flexible electronics.
This work presents a universal approach for synthesizing polyoxometalates (POMs)‐reinforced ionic liquid‐based gels (ILGs) and builds up an efficient bridge between them. The potential of POMs and ILGs across numerous fields, combined with structure–property–performance elucidation, has led to the identification of superior POMs‐improved ILGs suitable for the fabrication of self‐powered sensing systems.
The oxygen reduction reaction (ORR) is a key energy conversion process, which is critical for the efficient operation of fuel cells and metal–air batteries. Here, we report the significant ...enhancement of the ORR‐performance of commercial platinum‐on‐carbon electrocatalysts when operated in aqueous electrolyte solutions (pH 5.6), containing the polyoxoanion Fe28(μ3‐O)8(L‐(−)‐tart)16(CH3COO)2420−. Mechanistic studies provide initial insights into the performance‐improving role of the iron oxide cluster during ORR. Technological deployment of the system is demonstrated by incorporation into a direct formate microfluidic fuel cell (DFMFC), where major performance increases are observed when compared with reference electrolytes. The study provides the first examples of iron oxide clusters in electrochemical energy conversion and storage.
Significant oxygen reduction reaction reactivity enhancements are observed when aqueous solutions containing iron oxide clusters {Fe28} are used as electrolyte. Mechanistic, experimental and theoretical studies explore possible roles of this polyion in the electrocatalytic oxygen reduction.
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