Ionic covalent organic framework membranes (iCOFMs) hold great promise in ion conduction-relevant applications because the high content and monodispersed ionic groups could afford superior ion ...conduction. The key to push the upper limit of ion conductivity is to maximize the ion exchange capacity (IEC). Here, we explore iCOFMs with a superhigh ion exchange capacity of 4.6 mmol g
, using a dual-activation interfacial polymerization strategy. Fukui function is employed as a descriptor of monomer reactivity. We use Brønsted acid to activate aldehyde monomers in organic phase and Brønsted base to activate ionic amine monomers in water phase. After the dual-activation, the reaction between aldehyde monomer and amine monomer at the water-organic interface is significantly accelerated, leading to iCOFMs with high crystallinity. The resultant iCOFMs display a prominent proton conductivity up to 0.66 S cm
, holding great promise in ion transport and ionic separation applications.
State‐of‐the‐art proton exchange membranes (PEMs) often suffer from significantly reduced conductivity under low relative humidity, hampering their efficient application in fuel cells. Covalent ...organic frameworks (COFs) with pre‐designable and well‐defined structures hold promise to cope with the above challenge. However, fabricating defect‐free, robust COF membranes proves an extremely difficult task due to the poor processability of COF materials. Herein, a bottom‐up approach is developed to synthesize intrinsic proton‐conducting COF (IPC‐COF) nanosheets (NUS‐9) in aqueous solutions via diffusion and solvent co‐mediated modulation, enabling a controlled nucleation and in‐plane‐dominated IPC‐COF growth. These nanosheets allow the facile fabrication of IPC‐COF membranes. IPC‐COF membranes with crystalline, rigid ion nanochannels exhibit a weakly humidity‐dependent conductivity over a wide range of humidity (30–98%), 1–2 orders of magnitude higher than that of benchmark PEMs, and a prominent fuel cell performance of 0.93 W cm−2 at 35% RH and 80 °C arising from superior water retention and Grotthuss mechanism‐dominated proton conduction.
A bottom‐up approach based on the diffusion and solvent co‐mediated growth of covalent organic frameworks (COFs) is proposed to synthesize nanosheets of a highly crystalline, intrinsically proton‐conducting COF (IPC‐COF) in aqueous solution. The high‐quality IPC‐COF nanosheets allow the fabrication of defect‐free and robust IPC‐COF membranes that exhibit a weakly humidity‐dependent proton conduction and a prominent fuel‐cell performance.
In this study, imidazolium brushes tethered by ⁻NH₂-containing ligands were grafted onto the surface of a 2D material, MXene, using precipitation polymerization followed by quaternization. ...Functionalized MXene was embedded into chitosan matrix to prepare a hybrid alkaline anion exchange membrane. Due to high interfacial compatibility, functionalized MXene was homogeneously dispersed in chitosan matrix, generating continuous ion conduction channels and then greatly enhancing OH
conduction property (up to 172%). The ability and mechanism of OH
conduction in the membrane were elaborated based on systematic tests. The mechanical-thermal stability and swelling resistance of the membrane were evidently augmented. Therefore, it is a promising anion exchange membrane for alkaline fuel cell application.
The emergence of all‐organic frameworks is of fundamental significance, and designing such structures for anion conduction holds great promise in energy conversion and storage applications. Herein, ...inspired by the efficient anion transport within organisms, a de novo design of covalent organic frameworks (COFs) toward ultrafast anion transport is demonstrated. A phase‐transfer polymerization process is developed to acquire dense and ordered alignment of quaternary ammonium‐functionalized side chains along the channels within the frameworks. The resultant self‐standing COFs membranes exhibit one of the highest hydroxide conductivities (212 mS cm−1 at 80 °C) among the reported anion exchange membranes. Meanwhile, it is found that shorter, more hydrophilic side chains are favorable for anion conduction. The present work highlights the prospects of all‐organic framework materials as the platform building blocks in designing ion exchange membranes and ion sieving membranes.
The de novo design of covalent organic frameworks (COFs) affords a dense and ordered alignment of quaternary ammonium‐functionalized side chains along the intrinsic channels within the frameworks, rendering one of the highest hydroxide conductivities among the reported anion‐exchange membranes (AEMs), and demonstrating the feasibility of COFs as the building blocks for high‐performance AEMs.
Abstract
Covalent organic frameworks (COF), with rigid, highly ordered and tunable structures, can actively manipulate the synergy of entropic selectivity and enthalpic selectivity, holding great ...potential as next-generation membrane materials for ion separations. Here, we demonstrated the efficient separation of monovalent cations by COF membrane. The channels of COF membrane are decorated with three different kinds of acid groups. A concept of confined cascade separation was proposed to elucidate the separation process. The channels of COF membrane comprised two kinds of domains, acid-domains and acid-free-domains. The acid-domains serve as confined stages, rendering high selectivity, while the acid-free-domains preserve the pristine channel size, rendering high permeation flux. A set of descriptors of stage properties were designed to elucidate their effect on selective ion transport behavior. The resulting COF membrane acquired high ion separation performances, with an actual selectivity of 4.2–4.7 for K
+
/Li
+
binary mixtures and an ideal selectivity of ~13.7 for K
+
/Li
+
.
Covalent organic framework (COF) membranes hold potential for widespread applicability, but scalable fabrication is challenging. Here, we demonstrate the disorder‐to‐order transformation from ...amorphous polymeric membrane to crystalline COF membrane via monomer exchange. Solution processing is used to prepare amorphous membrane and the replacing monomer is selected based on the chemical and thermodynamical stability of the final framework. Reversible imine bonds allow the extraneous monomers to replace the pristine monomers within amorphous membrane, driving the transformation from disordered network to ordered framework. Incorporation of intramolecular hydrogen bonds enables the crystalline COF to imprint the amorphous membrane morphology. The COF membranes harvest proton conductivity up to 0.53 S cm−1 at 80 °C. Our strategy bridges amorphous polymeric and crystalline COF membranes for large‐scale fabrication of COF membranes and affords guidance on materials processing.
A disorder‐to‐order transformation strategy is developed for the scalable fabrication of highly crystalline covalent organic framework (COF) membrane from amorphous polymeric membrane via monomer exchange.
Abstract
The idea of spatial confinement has gained widespread interest in myriad applications. Especially, the confined short hydrogen-bond (SHB) network could afford an attractive opportunity to ...enable proton transfer in a nearly barrierless manner, but its practical implementation has been challenging. Herein, we report a SHB network confined on the surface of ionic covalent organic framework (COF) membranes decorated by densely and uniformly distributed hydrophilic ligands. Combined experimental and theoretical evidences have pointed to the confinement of water molecules allocated to each ligand, achieving the local enrichment of hydronium ions and the concomitant formation of SHBs in water-hydronium domains. These overlapped water-hydronium domains create an interconnected SHB network, which yields an unprecedented ultrahigh proton conductivity of 1389 mS cm
−1
at 90 °C, 100% relative humidity.
Abstract
3D ionic covalent organic framework (COF) membranes, which are envisioned to be able to break the trade-off between ion conductivity and ion selectivity, are waiting for exploitation. ...Herein, we report the fabrication of a 3D sulfonic acid-functionalized COF membrane (3D SCOF) for efficient and selective ion transport, using dual acid-mediated interfacial polymerization strategy. The 3D SCOF membranes possess highly interconnected ion transport channels, ultramicroporous pore sizes (0.97 nm), and abundant sulfonate groups (with a high ion exchange capacity of 4.1 mmol g
−1
), leading to high proton conductivity of 843 mS cm
−1
at 90 °C. When utilized in osmotic energy conversion, a high power density of 21.2 W m
−2
, and a remarkable selectivity of 0.976 and thus an exceptional energy conversion efficiency of 45.3% are simultaneously achieved. This work provides an alternative approach to 3D ionic COF membranes and promotes the applications of 3D COFs in ion transport and separation.
Graphene oxide (GO) membrane, bearing well-aligned interlayer nanochannels and well-defined physicochemical properties, promises fast proton transport. However, the deficiency of proton donor groups ...on the basal plane of GO and weak interlamellar interactions between the adjacent nanosheets often cause low proton conduction capability and poor water stability. Herein, we incorporate sulfonated graphene quantum dots (SGQD) into GO membrane to solve the above dilemma via synergistically controlling the edge electrostatic interaction and in-plane π–π interaction of SGQD with GO nanosheets. SGQD with three different kinds of electron-withdrawing groups are employed to modulate the edge electrostatic interactions and improve the water swelling resistant property of GO membranes. Meanwhile, SGQD with abundant proton donor groups assemble on the sp2 domain of GO via in-plane π–π interaction and confer the GO membranes with low-energy-barrier proton transport channels. As a result, the GO membrane achieves an enhanced proton conductivity of 324 mS cm–1, maximum power density of 161.6 mW cm–2, and superior water stability when immersed into water for one month. This study demonstrates a strategy for independent manipulation of conductive function and nonconductive function to fabricate high-performance proton exchange membranes.
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