Interlayer Interactions and Macroscopic Property Calculations of Squaric-Acid-Linked Zwitterionic Covalent Organic Frameworks: Structures, Photocatalytic Carrier Transport, and a DFT Study.

Squaric-acid-linked zwitterionic covalent organic frameworks (Z-COFs), assembled through interlayer interactions, are emerging as potential materials in the field of photocatalysis. However, the study of their interlayer interactions has been largely overlooked. To address this, this work systematically calculated interlayer interactions via density functional theory (DFT) and analyzed the differences in interlayer interactions of different structures of Z-COFs through interlayer slippage, planarity, and an independent gradient model based on the Hirshfeld partition (IGMH). Furthermore, it revealed the relationship between the interactions and the macroscopic photocatalytic carrier transport performance of the material. The results indicated that both preventing interlayer slippage and enhancing planarity can enhance the interlayer interactions of Z-COFs, thereby improving their macroscopic carrier transport performance in photocatalysis.

Self-Assembly Behavior, Aggregation Structure, and the Charge Carrier Transport Properties of S-Heterocyclic Annulated Perylene Diimide Derivatives.

The construction of high-performance n-type semiconductors is crucial for the advancement of organic electronics. As an attractive n-type semiconductor, molecular systems based on perylene diimide derivatives (PDIs) have been extensively investigated over recent years. Owing to the fascinating aggregated structure and high performance, S-heterocyclic annulated PDIs (SPDIs) are receiving increasing attention. However, the relationship between the structure and the electrical properties of SPDIs has not been deeply revealed, restricting the progress of PDI-based organic electronics. Here, we developed two novel SPDIs with linear and dendronized substituents in the imide position, named linear SPDI and dendronized SPDI, respectively. A series of structural and property characterizations indicated that linear SPDI formed a long-range-ordered crystalline structure based on helical supramolecular columns, while dendronized SPDI, with longer alkyl side chains, formed a 3D-ordered crystalline structure at a low temperature, which transformed into a hexagonal columnar liquid crystal structure at a high temperature. Moreover, no significant charge carrier transport signal was examined for linear SPDI, while dendronized SPDI had a charge carrier mobility of 3.5 × 10-3 cm2 V-1 s-1 and 2.1 × 10-3 cm2 V-1 s-1 in the crystalline and liquid crystalline state, respectively. These findings highlight the importance of the structure-function relationship in PDIs, and also offer useful roadmaps for the design of high-performance organic electronics for down-to-earth applications.

Synthesis of Vinylene-Linked Thiopyrylium-, Pyrylium-, and Pyridinium-Based Covalent Organic Frameworks by Acid-Catalyzed Aldol Condensation.

The development of new vinylene-linked covalent organic frameworks (COFs) with special ionic structure and high stability is challenging. Herein, we report a facile, general method for constructing ionic vinylene-linked thiopyrylium-based COFs from 2,4,6-trimethylpyrylium tetrafluoroborate and other common reagents by means of acid-catalyzed Aldol condensation. Besides, pyrylium-, and pyridinium-based COFs also can be prepared from the same monomer under slightly different reaction conditions. The COFs exhibited uniform nanofibrous morphologies with excellent crystallinities, special ionic structures, well-defined nanochannels, and high specific surface areas.

Covalent organic framework wrapped by graphene oxide as an efficient sulfur host for high performance lithium-sulfur batteries.

The practical application of lithium-sulfur battery is seriously limited by the loss of active substances and the deterioration of cycle stability caused by the 'shuttle effect' of lithium polysulfides (LiPSs). In this work, graphene oxide (GO) coated covalent organic framework (COF) compound materials were synthesized as sulfur host material in spray-drying process. The polar groups on COF can efficiently adsorb LiPSs through lithiophilic interaction, which can reduce the 'shuttle effect' caused by soluble LiPSs. Besides, GO in the outer layer can wrap discrete sulfur to reduce the loss of active substances, which further improves the cycle stability of the cathode. The COF@GO/S cathode exhibits a high initial specific capacity of 848.4 mAh g-1and retains a capacity of 601.1 mAh g-1after 500 cycles at 1 C counting with a low capacity fading of 0.058% per cycle.

Bifunctional Sulfhydryl-Based Polyimides for Highly Active Cathodes of Li-S Batteries.

Sulfhydryl-based polyimides were synthesized by the nucleophilic ring-opening reaction of thiolactone monomers (BPDA-T, ODPA-T, BTDA-T) with polyethylenimine (PEI), and they were coated on carbon nanotubes as host materials (BPTP@CNT, ODTP@CNT, and BTTP@CNT) of the sulfur cathode. BPTP@CNT/S, ODTP@CNT/S, and BTTP@CNT/S as cathode materials not only promote the covalent bonding of sulfur and polysulfide with sulfhydryl-based polyimides but also reduce the shuttle effect of soluble polysulfide in the redox process. Moreover, sulfhydryl-based polyimides can help improve the compatibility and interfacial contact between sulfur and conductive carbon while alleviating the volume expansion of the cathode. In addition, the conductive network of carbon nanotubes improves the electronic conductivity of the cathode materials. The BTTP@CNT/S cathode showed superior stability (the initial capacity was 902 mAh g-1 at 1C, and the capacity retention rate was 88.58% after 500 cycles) and the initial capacity could reach 718 mAh g-1 when the sulfur loading was 4.8 mg cm-2 (electrolyte/sulfur ratio: 10 µL mg-1), which fully proves the feasibility of the large-scale application of sulfhydryl-based polyimide materials.

F-regulated Ni2P-F3 nanosheets as efficient electrocatalysts for full-water-splitting and urea oxidation.

Heteroatomic anion doping represents a powerful approach for manipulating the electronic configuration of the active metal locus in electrocatalysts, resulting in enhanced multifunctional electrocatalytic properties in hydrogen/oxygen evolution reactions (HER/OER). Here, fluorine-tailored Ni2P-F3 nanosheets were synthesized and evaluated as a robust multifunctional electrocatalyst for HER, OER, and UOR. Our comprehensive experimental and theoretical investigations reveal that the anionic F effectively tailored the electronic states of the Ni2P-F3 nanosheets, resulting in an elevated d-band center and optimizing the sorption capacity of intermediates. In addition to thermodynamically and kinetically favoured redox reactions, F doping facilitates the reconstruction and generation of active γ-NiOOH. Resulting from the optimized electronic configuration and nanosheet architecture, outstanding catalytic activities are demonstrated by Ni2P-F3 with low overpotentials to reach 100 mA cm-2 for HER (177 mV) and OER (293 mV), surpassing Ni2P by 234 and 205 mV, respectively. Notably, 1.618 V is required for full-water-diversion to reach 10 mA cm-2, while 1.414 V is required with urea oxidation for 100 mA cm-2.

Theoretical design of new insensitive high energy metal complexes based on the double fused-ring insensitive ligands strategy.

CONTEXT: In this work, 24 new nitrogen-rich fused-ring energetic metal complexes were designed based on the double fused-ring insensitive ligands strategy. First, 7-nitro-3-(1H-tetrazol-5-yl)-[1,2,4]triazolo[5,1-c][1,2,4]triazin-4-amine and 6-amino-3-(4H,8H-bis([1,2,5]oxadiazolo)[3,4-b:3',4'-e]pyrazin-4-yl)-1,2,4,5-tetrazine-1,5-dioxide were linked together by coordinating with metals cobalt and copper. Then, three energetic groups (NH2, NO2, and C(NO2)3) were introduced into the system to modify the structure and adjust the performance. Then, their structures and properties were investigated theoretically; the effects of different metals and small energetic groups were studied also. Finally, 9 compounds which have both higher energy and lower sensitivity than the famous high energy compound compound 1,3,5,7-tetranitro-1,3,5,7-tetrazocine were selected out. In addition, it was found that copper, NO2, and C(NO2)3 could increase the energy while cobalt and NH2 would be helpful for reducing the sensitivity. METHODS: Calculations were performed at the TPSS/6-31G(d) level by using the Gaussian 09 software.

"d-electron interactions" induced CoV2O6-Fe-NF for efficient oxygen evolution reaction.

The investigation of cost-effective, highly efficient, and environmentally friendly non-noble-metal-based electrocatalysts is imperative for oxygen evolution reactions (OER). Herein, CoV2O6 grown on nickel foam (NF) was selected as the fundamental material, and Fe2+ is introduced through a simple Fe3+ immersion treatment to synthesize CoV2O6-Fe-NF. Fe2+ is transformed into high oxidation state Fe(2+δ)+ due to interactions between the 3d electrons of transition metals. In situ Raman spectroscopy analysis reveals the specific process of OER in the presence of Fe(2+δ)+. Being in a higher oxidation state, Fe(2+δ)+ provides more active sites, which is beneficial for the reaction between water molecules and the reactive sites of the electrocatalyst, ultimately enhancing the accelerated OER process. CoV2O6-Fe-NF exhibited an overpotential of only 298 mV at 100 mA cm-2 in 1 M KOH electrolyte, which is lower than that of CoV2O6-NF (348 mV), as well as the comparative samples: Fe-NF (390 mV) and NF (570 mV). The exploration of high performance, triggered synergistically by the cooperative effect of transition metal 3d electrons, provides insights into the design of transition metal electrocatalysts for highly efficient OER.

Zwitterionic and Hydrophilic Vinylene-Linked Covalent Organic Frameworks for Efficient Photocatalytic Hydrogen Evolution.

Developing effective synthetic strategies as well as broadening functionalities for zwitterionic materials that comprise moieties with equimolar cationic and anionic groups still remains a huge challenge. Herein, we develop two zwitterionic vinylene-linked covalent organic frameworks (Zi-VCOF-1 and Zi-VCOF-2) that are a type of novel hydrophilic material. Zi-VCOF-1 and Zi-VCOF-2 are obtained directly through the convenient Knoevenagel condensation of new sulfonic-pyridinium zwitterionic monomers with aromatic aldehyde derivatives. This is the first report on zwitterionic COFs being constructed by the bottom-up functionalization approach from predesigned zwitterionic monomers. Both Zi-VCOFs exhibit a high photocatalytic hydrogen evolution rate (HER) because of their appropriate optical property and outstanding hydrophilicity. Specifically, Zi-VCOF-1 and Zi-VCOF-2 show photocatalytic HER of 13,547 and 5057 µmol h-1 g-1, respectively. Interestingly, the photocatalytic HER of Zi-VCOF-1 is about 2.68 times of that of Zi-VCOF-2, although they differ by only one methyl group in sulfonic-pyridinium zwitterionic pairs. The photocatalytic HER of Zi-VCOF-1 is not only the highest in the vinylene-linked COFs but also outstanding among the most reported COFs. This is the first application of zwitterionic COFs for photocatalytic hydrogen evolution, which would open a new frontier in zwitterionic COFs and be helpful for the design of other photocatalytic materials.

Multi-function hollow nanorod as an efficient sulfur host accelerates sulfur redox reactions for high-performance Li-S batteries.

The "shuttle effect" of lithium polysulfides (LiPSs) leads to loss of active materials and the deterioration of cycle stability, which seriously restricts the practical progress of lithium-sulfur (Li-S) batteries. The diffusion of soluble discharge intermediate is the root cause of the above problems. Herein, we synthesized a porous organic framework material (HUT-8) based on triazine network, the polar groups above the hollow structure can not only adsorb LiPSs through electron donating effect, but also anchored cobalt (II) ions provide a large number of binding sites for the in-situ growth of CoS2. This ensured maximized exposure of catalytic centre and improve their interactions with sulfur redox species under the confinement of mesopores, which can catalytically accelerate capture/diffusion of LiPSs and precipitation/decomposition of Li2S. Based on the synergistic effect of the composite materials, the CoS2-HUT-8/S cathode maintained a capacity of 583 mAh g-1 after 500 cycles at 1 C, and a minimum capacity fading rate of 0.046% per cycle. A freestanding CoS2-HUT-8/S cathode with sulfur loading of 5.2 mg cm-2 delivered a high areal capacity of 4.01 mAh cm-2 under a lean electrolyte, which would provide great potential for the practical progress of Li-S batteries.

Thiadiazole-Derived Covalent Organic Framework Macroscopic Ultralight Aerogel.

Shaping covalent organic frameworks (COFs) into macroscopic objects for practical application remains a huge challenge. Herein, a new thiadiazole-derived COF macroscopic ultralight aerogel (NNS-VCOF) was prepared through acid-catalyzed aldol condensation between 2,5-dimethyl-1,3,4-thiadiazole and a tritopic aromatic aldehyde derivative. NNS-VCOF aerogel shows extremely low density (ca. 0.020 g cm-3), excellent mechanical properties (compression modulus of 16.65 kPa), thermal insulation properties (low thermal conductivity of 0.03270 W m-1 K-1 at 25 °C), and flame retardancy (quickly self-extinguishing after ignition) due to its three-dimensional sponge-like architecture and special nitrogen heterocyclic framework. To our delight, NNS-VCOF aerogel not only can be used as an outstanding macroscopic material but also shows efficient photocatalytic hydrogen evolution properties in a powder state because of the superhydrophilicity and appropriate optical properties.

Squaraine-linked zwitterionic COF modified LLZTO nanoparticles for high performance polymer composite electrolytes in Li-S batteries.

Lithium-sulfur (Li-S) batteries are severely restricted for practical application due to the polysulfide shuttle effect, Li dendrites and thermal runaway. The use of PEO-based polymer composite electrolytes (PCEs) as an alternative strategy suffers from limited lithium-ion conductivity with deficient long-range transfer route. Herein, Li6.4La3Zr1.4Ta0.6O12 (LLZTO) nanoparticles modified with an in situ-synthesized zwitterionic covalent organic framework layer (denoted as LLZTO@HUT4) were introduced into PEO-based PCEs. Zwitterionic HUT4 modified the lithiophobic LiOH/Li2CO3 layer on the surface of LLZTO nanoparticles, which could notably promote Li+ ion transport for superior electrochemical performance of PCEs. Additionally, the intermediate layer HUT4 located between LLZTO and PEO could further improve the mechanical properties of electrolytes due to the enhanced inorganic/organic interface compatibility and intermolecular interaction. As a result, the obtained LLZTO@HUT4-15%/PEO electrolyte exhibited a competent ionic conductivity of 0.73 mS cm-1 with a Li+ transference number of up to 0.74 at 60 °C. The assembled S@CNT|LLZTO@HUT4-15%/PEO|Li coin cell delivered a considerable initial discharge capacity of 1018 mA h g-1 at 0.2 C, with approximately 92.1% capacity retention after 100 cycles, elucidating an obviously suppressed shuttle effect.

Nucleophilic ring-opening of thiocyclic carbonates: A scheme to prepare sulfhydryl-rich binders for high-performance lithium-sulfur batteries.

Problems such as cathode collapse caused by volume change and shuttle effect of lithium polysulfides (LiPSs) limit the commercialization of Lithium-Sulfur (Li-S). Herein, we developed a sulfhydryl-containing multifunctional binder prepared by the nucleophilic ring-opening reaction of thiocyclic carbonates with amino groups. The binders (CNP-T and CNP-F) form sulfur-containing polymers with sulfur through the wet-slurry process, thereby effectively suppressing the shuttle effect. The abundant polar functional groups (e.g., -NH2, -CS(NH)-) in CNP-T and CNP-F can effectively adsorb LiPSs to weaken the shuttle effect, which is confirmed by both density functional theory (DFT) and experimental results. At the same time, their own hyperbranched network structure can also limit the volume change of the sulfur cathode. Therefore, the Li-S battery exhibits an initial specific capacity of 924.02 mAh/g and a decay rate of 0.033% when cycled at 1C for 500 cycles.

Triazine-based porous organic polymers with enhanced electronegativity as multifunctional separator coatings in lithium-sulfur batteries.

The commercialization of lithium-sulfur batteries is seriously affected by the shuttle behavior and slow conversion kinetics of polysulfides. Herein, a new porous organic polymer (POP) is synthesized and grown on reduced graphene oxide (rGO) in situ to improve battery performance, which serves as an efficient polysulfide adsorber and catalytic promoter for polysulfide conversion. The polar POP shows strong chemisorption to polysulfides, which is confirmed by a series of calculations and experimental results. As a popular conductive substrate, rGO offers an electron transport channel for sulfur and polysulfide conversion. Due to the synergistic functions of composite materials, the batteries with POP@rGO modified separators retain a high specific capacity of 697.3 mA h g-1 and a minimum capacity fading rate of 0.04% per cycle at 1C over 500 cycles. Besides, even at a high sulfur loading of 5 mg cm-2, a high area capacity of 4.27 mA h cm-2 can also be achieved, which shows that it has great potential in promoting the commercialization of lithium-sulfur batteries.

Theoretical design of novel high energy metal complexes based on two complementary oxygen-rich mixed ligands of 4-amino-4H-1,2,4-triazole-3,5-diol and 1,1'-dinitramino-5,5'-bistetrazole.

In this study, 16 new energetic metal complexes [M(DNABT)(ATDO), M=Cu, Ni] were designed using the mixed complex construct strategy, which was based on two complementary oxygen-rich high-energy ligands of 1,1'-dinitramino-5,5'-bistetrazole (DNABT) and 4-amino-4H-1,2,4-triazole-3,5-diol (ATDO), then combined with metals Cu and Ni, and further adjusted by the introduction of NO2 and NH2. The molecular and electronic structures, heat of formation (HOF), density, detonation velocity, detonation pressure, and sensitivity were investigated by the density functional theory method. The results showed that in metals, the position and amount of NO2/NH2 have great effects on the structure and property of metal complexes, and these effects coupled with each other. N-NO2 bond is the relatively weak bond, and its max length is related with the sensitivity closely. The designed metal complexes all have high HOF (673~868 kJ mol-1), high density (2.06~2.14 g cm-3), and ideal oxygen balance (- 19.2~- 6.7%), which further make them have higher detonation velocity (8.76~9.84 km s-1) and detonation pressure (37.4~46.6 GPa) than three famous high-energy compounds 1,3,5-trinitro-1,3,5-triazine (RDX); 1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX); or even 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane (CL-20). At the same time, they are less sensitive than RDX, HMX, and CL-20, making them potential candidates for high-energy density compounds.