It has been a longstanding challenge to rationally synthesize thin films of organic two-dimensional (2D) crystals with large single-crystalline domains. Here, we present a general strategy for the creation of 2D crystals of covalent organic frameworks (COFs) on the water surface, assisted by a charged polymer. The morphology of the preorganized monomers underneath the charged polymer on the water surface and their diffusion were crucial for the formation of the organic 2D crystals. Thin films of 2D COFs with an average single-crystalline domain size of around 3.57 ± 2.57 μm2 have been achieved, and their lattice structure, molecular structure, and grain boundaries were identified with a resolution down to 3 Å. The swing of chain segments and lattice distortion were revealed as key factors in compensating for the misorientation between adjacent grains and facilitating error corrections at the grain boundaries, giving rise to larger single-crystalline domains. The generality of the synthesis method was further proved with three additional 2D COFs. The oriented single-crystalline domains and clear grain boundaries render the films as model materials to study the dependence of the vertical conductivity of organic 2D crystals on domain sizes and chemical structures, and significant grain boundary effects were illustrated. This study presents a breakthrough in the controlled synthesis of organic 2D crystals with structural control at the molecular level. We envisage that this work will inspire further investigation into the microstructure–intrinsic property correlation of 2D COFs and boost their application in electronics.

Covalent organic frameworks (COFs) are crystalline porous polymers with designable structures and properties. Their crystallization typically relies on trial-and-error involving harsh conditions including organic solvents, presenting significant obstacles for rational design and large-scale production. Here, we present a liquid crystal directed synthesis methodology and its implementation for up to gram-scale production of highly crystalline COFs in water and air. It is compatible to monomers with different structures, shape, size, length of side chains, and electron-donating, electron-accepting and heterocyclic substitutions near reactive sites. 17 types of donor-acceptor two-dimensional COFs including 4 types of new ones and a three-Page 1 of 24 https://mc03.manuscriptcentral.com/ccsc CCS Chemistry dimensional COF with a yield of up to 94% were demonstrated, showing great generality of the method. The as-synthesized donor-acceptor COFs are organic semiconductors and contain macropores besides intrinsic mesopores which make them as attractive catalysts. The production of H 2 O 2 under visible light in water was studied and the structure-property relationships were revealed. The production rate reached 4347 μmol h -1 g cat -1 , which is about 467% better than that of the benchmark photocatalyst g-C 3 N 4 . This study will inspire the mild synthesis and scale-up of a wide spectrum of COFs and organic semiconductors as efficient catalysts, promote their structure-property investigation, and boost their applications.

Designing cost‐effective, highly active, and durable platinum (Pt)‐based electrocatalysts is a crucial endeavor in electrochemical hydrogen evolution reaction (HER). Herein, the low‐content Pt (0.8 wt%)/tungsten oxide/reduced graphene oxide aerogel (LPWGA) electrocatalyst with excellent HER activity and durability is developed by employing a tungsten oxide/reduced graphene oxide aerogel (WGA) obtained from a facile solvothermal process as a support, followed by electrochemical deposition of Pt nanoparticles. The WGA support with abundant oxygen vacancies and hierarchical pores plays the roles of anchoring the Pt nanoparticles, supplying continuous mass transport and electron transfer channels, and modulating the surface electronic state of Pt, which endow the LPWGA with both high HER activity and durability. Even under a low loading of 0.81 μgPt cm−2, the LPWGA exhibits a high HER activity with an overpotential of 42 mV at 10 mA cm−2, an excellent stability under 10000‐cycle cyclic voltammetry and 40 h chronopotentiometry at 10 mA cm−2, a low Tafel slope (30 mV dec−1), and a high turnover frequency of 29.05 s−1 at η = 50 mV, which is much superior to the commercial Pt/C and the low‐content Pt/reduced graphene oxide aerogel. This work provides a new strategy to design high‐performance Pt‐based electrocatalysts with greatly reduced use of Pt.

Main observation and conclusion Imine‐linked covalent organic frameworks (COFs) have attracted extensive attention due to designable structures, tunable properties, and excellent thermal and chemical stability. They were typically obtained as insoluble and unprocessable powders, which seriously limits their full promise. Progress has been made in the synthesis of thin films of imine‐linked COFs by interfacial synthesis. However, the synthesis of highly crystalline, self‐supporting thin films of COFs remains challenging. Here, we employed a surfactants‐mediated method to synthesize such films at an air‐water interface, showed the films could be transferred onto arbitrary substrates on demand, and demonstrated the generality of the methodology with two different COFs. We found that the length of hydrophobic segments of surfactants played a key role in determination of the crystallinity and single crystalline domain size of the films. This work provides a feasible strategy to generate highly crystalline thin films of COFs.

Despite superb instrumental resolution in modern transmission electron microscopes (TEM), high-resolution imaging of organic two-dimensional (2D) materials is a formidable task. Here, we present that the appropriate selection of the incident electron energy plays a crucial role in reducing the gap between achievable resolution in the image and the instrumental limit. Among a broad range of electron acceleration voltages (300 kV, 200 kV, 120 kV, and 80 kV) tested, we found that the highest resolution in the HRTEM image is achieved at 120 kV, which is 1.9 Å. In two imine-based 2D polymer thin films, unexpected molecular interstitial defects were unraveled. Their structural nature is identified with the aid of quantum mechanical calculations. Furthermore, the increased image resolution and enhanced image contrast at 120 kV enabled the detection of functional groups at the pore interfaces. The experimental setup has also been employed for an amorphous organic 2D material.