Crystalline Porphyrazine-Linked Fused Aromatic Networks with High Proton Conductivity.

Fused aromatic networks (FANs) have been studied in efforts to overcome the low physicochemical stability of metal-organic frameworks (MOFs) and covalent organic frameworks (COFs), while preserving crystallinity. Herein, we describe the synthesis of a highly stable and crystalline FAN (denoted as Pz-FAN) using pyrazine-based building blocks to form porphyrazine (Pz) linkages via an irreversible reaction. Unlike most COFs and FANs, which are synthesized from two different building blocks, the new Pz-FAN is formed using a single building block by self-cyclotetramerization. Controlled and optimized reaction conditions result in a highly crystalline Pz-FAN with physicochemical stability. The newly prepared Pz-FAN displayed a high magnitude (1.16×10-2  S cm-1 ) of proton conductivity compared to other reported FANs and polymers. Finally, the Pz-FAN-based membrane was evaluated for a proton-exchange membrane fuel cell (PEMFC), which showed maximum power and current densities of 192 mW cm-2 and 481 mA cm-2 , respectively.

Abrading bulk metal into single atoms.

Single-atom catalysts have recently attracted considerable attention because of their highly efficient metal utilization and unique properties. Finding a green, facile method to synthesize them is key to their widespread commercialization. Here we show that single-atom catalysts (including iron, cobalt, nickel and copper) can be prepared via a top-down abrasion method, in which the bulk metal is directly atomized onto different supports, such as carbon frameworks, oxides and nitrides. The level of metal loading can be easily tuned by changing the abrasion rate. No synthetic chemicals, solvents or even water were used in the process and no by-products or waste were generated. The underlying reaction mechanism involves the mechanochemical force in situ generating defects on the supports, then trapping and stably sequestering atomized metals.

Fused Aromatic Network with Exceptionally High Carrier Mobility.

Recently, studies of 2D organic layered materials with unique electronic properties have generated considerable interest in the research community. However, the development of organic materials with functional electrical transport properties is still needed. Here, a 2D fused aromatic network (FAN) structure with a C5 N basal plane stoichiometry is designed and synthesized, and thin films are cast from C5 N solution onto silicon dioxide substrates. Then field-effect transistors are fabricated using C5 N thin flakes as the active layer in a bottom-gate top-contact configuration to characterize their electrical properties. The C5 N thin flakes, isolated by polydimethylsiloxane stamping, exhibit ambipolar charge transport and extraordinarily high electron (996 cm2 V-1 s-1 ) and hole (501 cm2 V-1 s-1 ) mobilities, surpassing the performance of most pristine organic materials without doping. These results demonstrate their vast potential for applications in thin-film optoelectronic devices.

Vertical two-dimensional layered fused aromatic ladder structure.

Planar two-dimensional (2D) layered materials such as graphene, metal-organic frameworks, and covalent-organic frameworks are attracting enormous interest in the scientific community because of their unique properties and potential applications. One common feature of these materials is that their building blocks (monomers) are flat and lie in planar 2D structures, with interlayer π-π stacking, parallel to the stacking direction. Due to layer-to-layer confinement, their segmental motion is very restricted, which affects their sorption/desorption kinetics when used as sorbent materials. Here, to minimize this confinement, a vertical 2D layered material was designed and synthesized, with a robust fused aromatic ladder (FAL) structure. Because of its unique structural nature, the vertical 2D layered FAL structure has excellent gas uptake performance under both low and high pressures, and also a high iodine (I2) uptake capacity with unusually fast kinetics, the fastest among reported porous organic materials to date.

Dissociating stable nitrogen molecules under mild conditions by cyclic strain engineering.

All quiet on the nitrogen front. The dissociation of stable diatomic nitrogen molecules (N2) is one of the most challenging tasks in the scientific community and currently requires both high pressure and high temperature. Here, we demonstrate that N2 can be dissociated under mild conditions by cyclic strain engineering. The method can be performed at a critical reaction pressure of less than 1 bar, and the temperature of the reaction container is only 40°C. When graphite was used as a dissociated N* receptor, the normalized loading of N to C reached as high as 16.3 at/at %. Such efficient nitrogen dissociation is induced by the cyclic loading and unloading mechanical strain, which has the effect of altering the binding energy of N, facilitating adsorption in the strain-free stage and desorption in the compressive strain stage. Our finding may lead to opportunities for the direct synthesis of N-containing compounds from N2.

Direct Synthesis of a Covalent Triazine-Based Framework from Aromatic Amides.

There have been extensive efforts to synthesize crystalline covalent triazine-based frameworks (CTFs) for practical applications and to realize their potential. The phosphorus pentoxide (P2 O5 )-catalyzed direct condensation of aromatic amide instead of aromatic nitrile to form triazine rings. P2 O5 -catalyzed condensation was applied on terephthalamide to construct a covalent triazine-based framework (pCTF-1). This approach yielded highly crystalline pCTF-1 with high specific surface area (2034.1 m2 g-1 ). At low pressure, the pCTF-1 showed high CO2 (21.9 wt % at 273 K) and H2 (1.75 wt % at 77 K) uptake capacities. The direct formation of a triazine-based COF was also confirmed by model reactions, with the P2 O5 -catalyzed condensation reaction of both benzamide and benzonitrile to form 1,3,5-triphenyl-2,4,6-triazine in high yield.