phase-separated copolymer membranes, often suffer from dramatically declined proton conductivity at low relative humidity (RH), [6-10] because the severe water loss under low RH destructs watermediated hydrogen-bonding networks. [8,11] For decades, great effort has been devoted to reduce the humidity-dependence of conductivity through preserving membrane hydration under low RH, such as incorporating hydrophilic groups [12,13] or hygroscopic porous nanofillers into membranes [7,14] to improve water retention properties, and installing nanovalves to retard water desorption of membranes. [2] However, the water retention remains a daunting challenge due to the "flexible polymer networks" nature of these PEMs. The amorphous, flexible ion nanochannels are prone to shrinking and even breaking upon dehydration, leading to poorly connected water channels and consequently exponential decline in conductivity and fuel cell performance. [6,15] Therefore, the design of electrolyte materials with weakly humidity-dependent proton-conducting feature remains a challenge. Materials with crystalline and rigid nanochannels are able to firmly retain water by capillary forces [16-20] and may promote membrane hydration, thereby facilitating proton transport efficiently over a wide range of humidity. Covalent organic frameworks (COFs), a class of crystalline porous polymers with pre-designable pore structures, hold grand promise. [21-23] Unlike amorphous, flexible crosslinked networks, the crystalline, rigid organic frameworks of COFs are expected to afford well-defined and stable proton-conducting nanochannels, [24-30] as well as good water retention capability. [18] However, leveraging COF materials in the field of COF-based PEMs for practical application remains a great challenge arising from the poor processing ability of COF materials and the poor structural integrity of COF membranes. Moreover, the proton transport mechanism in crystalline and rigid nanochannels of COF membranes remains elusive. Herein, we report a diffusion and solvent co-mediated modulation strategy for the direct synthesis of highly crystalline IPC-COF nanosheets (NUS-9) that can be readily processed into defect-free, robust IPC-COF membranes by subsequent vacuum-assisted self-assembly. These IPC-COF membranes exhibit weakly humidity-dependent conductivity and fuel cell performance over a wide range of humidity (30-98%). We further demonstrate that the crystalline and rigid ion nanochannels render the IPC-COF membranes exceptional 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...

Covalent organic frameworks (COFs) with intrinsic, tunable, and uniform pores are potent building blocks for separation membranes, yet poor processing ability and long processing time remain grand challenges. Herein, we report an engineered solid−vapor interface to fabricate a highly crystalline two-dimensional COF membrane with a thickness of 120 nm in 9 h, which is 8 times faster than that in the reported literature. Due to the ultrathin nature and ordered pores, the membrane exhibited an ultrahigh permeance (water, ∼411 L m −2 h −1 bar −1 and acetonitrile, ∼583 L m −2 h −1 bar −1 ) and excellent rejection of dye molecules larger than 1.4 nm (>98%). The membrane exhibited long-term operation which confirmed its outstanding stability. Our solid−vapor interfacial polymerization method may evolve into a generic platform to fabricate COFs and other organic framework membranes

Covalent organic framework (COF) membranes hold potential for widespread applicability,b ut scalable fabrication is challenging.H ere,w ed emonstrate the disorderto-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 allowt he extraneous monomers to replace the pristine monomers within amorphous membrane,d riving the transformation from disordered network to ordered framework. Incorporation of intramolecular hydrogen bonds enables the crystalline COF to imprint the amorphous membrane morphology.T he COF membranes harvest proton conductivity up to 0.53 Scm À1 at 80 8 8C. Our strategy bridges amorphous polymeric and crystalline COF membranes for large-scale fabrication of COF membranes and affords guidance on materials processing.

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−1, 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−1, holding great promise in ion transport and ionic separation applications.

Lamellar membranes with two-dimensional nanofluidic channels hold great promise in harvesting osmotic energy from salinity gradients. However, the power density is often limited by the high transmembrane resistance primarily caused...

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.

Fabrication of covalent organic framework (COF) membranes for molecular transport has excited highly pragmatic interest as a low energy and cost-effective route for molecular separations. However, currently, most COF membranes are assembled via a one-step procedure in liquid phase(s) by concurrent polymerization and crystallization, which are often accompanied by a loosely packed and less ordered structure. Herein, we propose a two-step procedure via a phase switching strategy, which decouples the polymerization process and the crystallization process to assemble compact and highly crystalline COF membranes. In the pre-assembly step, the mixed monomer solution is casted into a pristine membrane in the liquid phase, along with the completion of polymerization process. In the assembly step, the pristine membrane is transformed into a COF membrane in the vapour phase of solvent and catalyst, along with the completion of crystallization process. Owing to the compact and highly crystalline structure, the resultant COF membranes exhibit an unprecedented permeance (water ≈ 403 L m−2 bar−1 h−1 and acetonitrile ≈ 519 L m−2 bar−1 h−1). Our two-step procedure via phase switching strategy can open up a new avenue to the fabrication of advanced organic crystalline microporous membranes.

Fabricating covalent organic frameworks (COFs) membranes with tight structure,w hich can fully utilizew elldefined framework structure and thus achieve superior conduction performance,r emains ag rand challenge.H erein, through molecular precursor engineering of COFs,wereported the fabrication of tight COFs membrane with the everreported highest hydroxide ion conductivity over 200 mS cm À1 at 80 8 8C, 100 %RH. Six quaternary ammonium-functionalized COFs were synthesized by assembling functional hydrazides and different aldehyde precursors.I na no rganic-aqueous reaction system, the impact of the aldehyde precursors with different size, electrophilicity and hydrophilicity on the reaction-diffusion process for fabricating COFs membranes was elucidated. Particularly,m ore hydrophilic aldehydes were prone to push the reaction zone from the interface region to the aqueous phase of the reaction system, the tight membranes were thus fabricated via phase-transfer polymerization process, conferring around 4-8 times the anion conductivity over the loose membranes via interfacial polymerization process.