Conjugated Three-Dimensional High-Connected Covalent Organic Frameworks for Lithium-Sulfur Batteries

A Coordination Supramolecular Network Janus Separator Boost Sulfur Redox Dynamics in Lithium-Sulfur Batteries

Lithium-sulfur (Li-S) batteries are limited in practical application due to the dissolution and shuttle effect of lithium polysulfides (LiPSs) intermediates. Herein, a multifunctional Janus separator is designed that integrates the zirconium-based coordination supramolecular network (Zr-CSN) with the polypropylene (PP) membrane to fabricate Zr-CSN@PP. The Zr-CSN@PP constructs a barrier on the side of the sulfur cathode to block the passage of polysulfides, and the nanoporous structure of Zr-CSN transfers lithium ions quickly. The active zirconium sites and abundant oxygen-containing groups of Zr-CSN adsorb and catalyze the polysulfides effectively, which has been proved by experiments and theoretical calculations. Zr-CSN@PP promotes the migration of Li+ (the lithium-ion transference number is 0.63) and improves the kinetics of sulfur evolution reactions, enhancing the electrochemical performance of Li-S batteries. The Li-S battery with Zr-CSN@PP separator has a capacity of 650.63 mAh g-1 after 280 cycles at 0.5 C (average decay of 0.2% per cycle), and a capacity of 422.48 mAh g-1 after 400 cycles at 2 C. This concept of porous coordination supramolecular networks Janus separator provides a broad prospect for advanced Li-S batteries.

New materials for lithium-sulfur batteries: challenges and future directions

This review explores recent advances in lithium-sulfur (Li-S) batteries, promising next-generation energy storage devices known for their exceptionally high theoretical energy density (∼2500 W h kg-1), cost-effectiveness, and environmental advantages. Despite their potential, commercialization remains limited by key challenges such as the polysulfide shuttle effect, sulfur's insulating nature, lithium metal anode instability, and thermal safety concerns. This review provides a comprehensive and forward-looking perspective on emerging material strategies-focusing on cathode, electrolyte, and anode engineering-to overcome these barriers. Special emphasis is placed on advanced sulfur-carbon composites, including three-dimensional graphene frameworks, metal-organic frameworks (MOFs), covalent organic frameworks (COFs), and MXene-based materials, which have demonstrated significant improvements in sulfur utilization, redox kinetics, and cycling stability. Innovations in electrolytes-particularly solid-state and gel polymer systems-are discussed for their roles in suppressing polysulfide dissolution and enhancing safety. This review also examines lithium metal anode protection strategies, such as use of artificial SEI layers and 3D lithium scaffolds and lithium alloying. Finally, it discusses critical issues related to large-scale manufacturing, safety, and commercial scalability. With ongoing innovation in multifunctional materials and electrode design, Li-S batteries are well positioned to transform energy storage for electric vehicles, portable electronics, and grid-scale systems.

Applications of COFs and Their Derivatives in Photocatalysis for Energy Production and Harmful Substance Degradation

Photocatalytic technology has attracted considerable attention in recent years due to its significant potential in environmental protection and energy conversion. Covalent organic frameworks (COFs), a novel class of porous materials, demonstrate remarkable photocatalytic performance owing to their high surface areas, tunable pore sizes, permanent porosities, and customizable functionalities. This review provides a comprehensive overview of the application of COFs in photocatalysis. In energy-related applications, COFs effectively catalyze hydrogen (H2) and hydrogen peroxide (H2O2) generation, and uranium (U(VI)) extraction from seawater, thereby offering new avenues for sustainable energy generation. In environmental remediation, COFs exploit photocatalytic properties to reduce carbon dioxide (CO2) emissions and degrade antibiotics in wastewater, thereby contributing to greenhouse gas mitigation and the enhancement of water quality. The review further explores the underlying mechanisms of COFs in photocatalytic H2 and H2O2 generation, U(VI) reduction, CO2 reduction, and antibiotic degradation, emphasizing the pivotal role of the COF structure in governing photocatalytic performance. Nevertheless, challenges persist concerning the stability, catalytic efficiency, and scalability of COFs. Future research should prioritize optimizing synthesis methods, tuning structural features, and enhancing the stability and performance of COFs to facilitate their practical applications. These advancements are crucial for promoting the widespread adoption of photocatalytic technologies in the energy and environmental sectors.

Facilitating efficient catalytic conversion of polysulfides in lithium-sulfur batteries via self-assembled hydrogen-bond-rich covalent organic frameworks

The widespread commercialization of lithium-sulfur (Li-S) batteries is hindered by two critical challenges: sluggish redox kinetics and the detrimental polysulfide shuttle effect. In this study, we present a novel approach utilizing hydrogen-bond-rich covalent organic frameworks (TTP@PVDF50), synthesized through an in situ self-assembly process incorporating polymeric guest species. These covalent organic frameworks (COFs), when integrated into the separators of Li-S batteries, preserve their intrinsic porosity and crystallinity, while the abundant fluorine-rich sites and well-defined pore structures enhance lithium-ion (Li+) transport kinetics. The hydrogen-bond-rich nature of the COFs provides an effective strategy to mitigate the polysulfide shuttle, leveraging both spatial hindrance and strong polar interactions for enhanced adsorption. Density functional theory (DFT) calculations and in situ Raman spectroscopy reveal that the F∙∙∙OH hydrogen bonding network in the TTP@PVDF50 composite significantly accelerates Li+ migration and catalyzes the conversion of LiPSs. The modified separator demonstrates a high discharge capacity of 1420.2 mAh g-1 at 0.2 C (1 C=1675 mAh g-1), alongside remarkable anti-self-discharge performance with only 9.0% capacity loss. Notably, the Li-S battery with a high sulfur loading (4.59 mg cm-2) and a lean electrolyte (6 µL mg-1) retains over 83% of its capacity, underscoring the effectiveness of this strategy in advancing the performance and longevity of Li-S batteries.

Highly Crystalline and Flexible Covalent Organic Frameworks: Advancing Efficient Iodine Adsorption

Flexible covalent organic frameworks (COFs) offer distinct advantages in elasticity and adaptability over rigid COFs, but these benefits often come at the expense of crystallinity due to challenges in polymerization, complicating both synthesis and structural characterization. Current research primarily employs single flexible monomers, which limits the tunability of these frameworks. In this study, we introduce two highly crystalline, flexible COFs, ZCST-102 and ZCST-103, constructed from dual flexible monomers. These COFs exhibit large channels, permanent porosity, high chemical stability, and exceptional crystallinity, along with enhanced structural flexibility. Notably, they achieve an iodine vapor adsorption capacity of up to 4.71 g ⋅ g-1. X-ray photoelectron spectroscopy, Raman spectroscopy, and electron paramagnetic resonance spectroscopy further elucidate the interactions between iodine and the framework structures. This work emphasizes the value of incorporating flexible building blocks to maintain crystallinity while imparting functional versatility, advancing the design of dynamic porous materials.

Thiazolium-Linked Crystalline Porous Covalent Organic Frameworks for Mixed Electronic-Ionic Transport

Developing efficiently mixed electronic-ionic (MEI) conductive microcosmic pathways within a single functional material is essential yet challenging for electronic devices. Covalent organic frameworks (COFs) feature pre-designed functionalities and uniform pores, making them highly desirable platforms for transporting electrons and ions. However, for MEI conductive COFs, achieving high crystallinity when incorporating high-density ionic groups within the extensively π-electron delocalized skeletons remain a challenge due to intermolecular interactions. Herein, we reported a "pre-polymerization followed by self-ionization" approach to synthesize new thiazolium-linked COFs (MEICOFs, M═Cu, Co, Fe), where the ionic groups synthesized following the connection of building blocks. MEICOFs demonstrated broad ultraviolet-visible-near-infrared absorption bands and narrow bandgaps. As a proof of concept, the mixed electronic and hydroxide ionic conductivity of CuEICOF was determined to be 55.2 and 0.01 S m-1, respectively. Moreover, MEICOFs film could directly catalyze the oxygen reduction reaction without additional conductive agent and the rotation of the electrode.

High-Connectivity 3D Covalent Organic Frameworks with pdp Net for Efficient C2H2/CO2 Separation

High-connectivity 3D covalent organic frameworks (COFs) have garnered significant attention due to their structural complexity, stability, and potential for functional applications. However, the synthesis of 3D COFs using mixed high-nodal building units remains a substantial challenge. In this work, we introduce two novel 3D COFs, JUC-661 and JUC-662, which are constructed using a combination of D2h-symmetric 8-nodal and D3h-symmetric 6-nodal building blocks. These COFs feature an unprecedented [8+6]-c pdp net with rare mesoporous polyhedral cages (~3.9 nm). Remarkably, JUC-661 and JUC-662 exhibit outstanding separation capabilities, achieving adsorption selectivities of 4.3 and 5.9, respectively, for C2H2/CO2 (1/1, v/v) mixtures. Dynamic breakthrough experiments confirm their excellent separation capability, maintaining this performance even under conditions of 100 % humidity. Monte Carlo simulations and DFT calculations indicate that the exceptional adsorption performance is attributed to the well-defined pore cavities of the COFs, with fluorination of the building unit further enhancing C2H2 selectivity through improved electrostatic and host-guest interactions. This study expands the structural diversity of COFs and highlights their potential for low-energy separation processes.

Three-Dimensional Covalent Organic Frameworks with jcg Topology Based on a Trinodal Strategy

The development of three-dimensional (3D) covalent organic frameworks (COFs) holds significant promise for various applications, but the conventional uninodal or binodal design strategies limit their structural diversity. In this work, we present a novel trinodal strategy for the synthesis of 3D COFs featuring both microporous and mesoporous nanochannels. Using powder X-ray diffraction (PXRD), computational simulations, and high-resolution transmission electron microscopy (HR-TEM), we demonstrate that employing an 8-c building block with reduced symmetry, which can be considered as 4- and 3-connected subunits, along with planar 4-c building blocks, results in an unprecedented [4 + 3 + 4]-c jcg net. This structure features rare saddle-shaped eight-membered rings and mirror-symmetrical chains. Furthermore, the incorporation of chromophore pyrene and redox-active triphenylamine components, coupled with structural conjugation, imparts tunable photophysical and electronic properties to these COFs, making them promising candidates for photocatalytic H2O2 production. This work highlights the potential of the trinodal strategy in creating intricate COF architectures and enhances their applicability in heterogeneous photocatalysis.

The Unexploring Optoelectronic Features in Organic Trans-Dimensional Materials of Gridofluorenes at the Nanoscale

Organic grido-architectures offer not only state-of-the-art models for exploring the complex relationships of multicarrier coherence among excitons, charges, photons, electrons, and phonons but also organic high-dimensional nanomaterials for flexible electronics and organic intelligence. Herein, we initiate the fundamental progress and perspective on gridofluorene-based zero-, one-, two-, and three-dimensional nanomolecules and their optoelectronic features. From the future point of view, the sterically trans-dimensional and hierarchically cross-scale effects of these covalent frameworks and nanostructures are discussed on their photophysical, electrical, mechanical and thermal properties. Organic multiscale systems, with the feature of synergistically molecule-programmable integration of diverse functionalities, open a bright door to flexible electronics, intelligent molecules, devices, systems, and even organobots as well as artificially intelligent and robotic chemists (AiRCs).

Unveiling Ion-Pairing and Anion Dual Charge Carrier in Ca-Organic Batteries

Calcium-organic batteries offer sustainable energy storage with high voltage, yet their reaction mechanisms remain unclear. Here, a hidden dual-ion charge storage mechanism is unveiled in poly(anthraquinone imide) (PAQI) using Ca(TFSI)₂/ether-based electrolytes, challenging the conventional Ca2⁺-only storage model. It is demonstrated that Ca2⁺-TFSI⁻ ion pairs co-bind to carbonyl groups during the first electron transfer, followed by TFSI⁻ dissociation to activate adjacent carbonyl sites in the second step-a process reversible upon charging. This mechanism critically depends on electrolyte solvation structures: G4 (tetraglyme) uniquely stabilizes monodentate CaTFSI⁺ contact ion pairs (versus multidentate aggregates in [G1 (monoglyme)/G2 (diglyme)] due to its optimal Ca2⁺ solvation energy, enabling exceptional performance. The PAQI/G4 system achieves a discharge capacity of 114 mAh g⁻¹ at 20 mA g⁻¹ and ultralong cycling (10 000 cycles with 94.5% capacity retention at 1000 mA g⁻¹), surpassing prior calcium-organic batteries at room temperature. This work redefines cation-anion interplay in organic electrodes and establishes electrolyte solvation engineering as a pivotal strategy for high-performance, durable calcium battery systems.

Heteroatom-Synergistic Effect on Anchoring Polysulfides In Chalcone-Linked Nanographene Covalent Organic Frameworks for High-Performance Li─S Batteries

Lithium-sulfur (Li─S) batteries are an attractive option for future energy storage devices because they offer higher theoretical specific capacity, energy density, and cost-effectiveness than commercial lithium-ion batteries. However, the practical applications of Li─S batteries are significantly limited by the shuttle effect caused by intermediate lithium polysulfides (LiPSs) and slow redox kinetics. In this study, the molecular engineering of chalcone-linked, sp2-bonded nanographene-type covalent organic frameworks (COFs) as sulfur hosts is reported to enhance interactions with LiPSs, thereby effectively suppressing the shuttle effect. The developed sulfur-hosting cathode material demonstrated outstanding battery performance, surpassing most reported materials by achieving a specific capacity of 1228 mA h g-1 at 0.5C, with 80% retention after 500 cycles and an average Coulombic Efficiency (C.E.) of 99%. Additionally, the mechanisms of sulfur immobilization, the subsequent conversion into lithium polysulfides (LiPSs), and their binding energies with COFs are investigated using density functional theory (DFT) calculations. These findings offer valuable insights into the structure-property relationships essential for developing more efficient sulfur-hosting cathodes.

Curvature-Induced Electron Delocalization Activates the Bifunctional Catalytic Activity of COF/MXene for High-Performance Lithium-Sulfur Batteries

Covalent organic frameworks (COFs) have shown promise as bifunctional catalysts to simultaneously mitigate shuttle effects and Li dendrite issues of lithium-sulfur (Li-S) batteries. However, the inherent low conductivity of the COFs has significantly limited their catalytic activity and stability. Herein, bifunctional catalytic activity and durability of the COF/MXene heterostructure are activated by tuning the surface curvatures of COFs interfaced with MXene. The increased curvature of COFs could induce enhanced electron delocalization and alter heterostructure geometry, which in turn strengthens lithium polysulfide adsorption, lowers energy barriers, and stabilizes catalytic sites to promote sulfur redox reactions. Concurrently, the hierarchical COF/MXene structure improves electrolyte penetration and wettability, facilitates rapid ion transport, and homogenizes the Li-ion flux distribution, thus achieving uniform lithium deposition. Consequently, the 1D-COF/MXene Li-S batteries demonstrate a high-rate capacity of 926 mA h g-1 at 4C, a stable cycling performance with a reversible capacity of 589 mA h g-1 at 3C after 500 cycles, and a high reversible capacity of 604 mA h cm-2 with a sulfur loading of 3.5 mg cm-2 under a low electrolyte-to-sulfur ratio of 10 μL mg-1. This work offers an efficacious approach to regulate catalytic activity and stability of catalysts.

A conjugated porous triazine-linked polyimide host with dual confinement of polysulfides for high-performance lithium-sulfur batteries

In the quest for next-generation energy storage solutions, lithium-sulfur (Li-S) batteries present exceptional potential due to their high energy density and cost-effectiveness. Nevertheless, significant challenges, such as the shuttle effect of lithium polysulfides (LiPSs) and inadequate sulfur utilization, have impeded their practical application. In this study, we report the design and synthesis of a novel covalent organic polymer that integrates a triazine-linked framework with carbonyl-enriched polyimide moieties, serving as a highly effective sulfur host for Li-S batteries. This engineered polymer not only provides abundant micropores for the physical confinement of LiPSs, but also facilitates robust chemical interaction through synergistic N-Li and O-Li bonding. The hierarchical porous architecture enhances sulfur loading, while the extended π-conjugation promotes rapid electron transport during LiPSs conversion. Consequently, the composite cathode achieves an impressive specific capacity of 1352 mAh g-1 at 0.1C, along with sustained cyclic stability (453 mAh g-1 after 400 cycles at 4C). These findings highlight the potential of multifunctional polymeric hosts in addressing critical limitations of Li-S batteries, offering a new blueprint for further developments in the field of high-performance energy storage systems.

Porphyrin-Based Covalent Organic Frameworks for CO2 Photo/Electro-Reduction

Photo/electro-catalytic CO2 reduction into high-value products are promising strategies for addressing both environmental problems and energy crisis. Duo to their advantageous visible light absorption ability, adjustable optic/electronic properties, definite active center, post-modification capability, and excellent stability, porphyrin-based covalent organic frameworks (COFs) have emerged as attractive photo/electro-catalysts towards CO2 reduction. In this review, the research progress of the porphyrin-based COFs for photo/electro-catalytic CO2 reduction is summarized including the design principles, catalytic performance, and reaction mechanism. In addition, this review also presents some challenges and prospects for the application of porphyrin-based COFs in photo/electro-catalytic CO2 reduction, laying the base for both fundamental research and application efforts.

Three-Dimensional Covalent Organic Framework with Dense Lithiophilic Sites as Protective Layer to Enable High-Performance Lithium Metal Battery

Lithium (Li) metal batteries with remarkable energy densities are restrained by short lifetime and low Coulombic efficiency (CE), resulting from the accumulative Li dendrites and dead Li during cycling. Here, we prepared a new three-dimensional (3D) covalent organic framework (COF) with dense lithiophilic sites (heteoatom weight contents of 32.32 wt %) as an anodic protective layer of Li metal batteries. The 3D COF was synthesized using a [6+4] synthesis strategy by inducing flexible 6-connected cyclotriphosphazene derivative aldehyde and 4-connected porphyrin-based tetraphenylamines. Both phosphazene and porphyrin rings in the COF served as electron-rich and lithiophilic sites, enhancing a homogeneous Li+ flux via 3D direction towards highly smooth and compact Li deposition. The Li/Por-PN-COF-Cu cells achieved a record average CE of 99.1 % for 320 cycles with smooth Li deposition. Meanwhile, the abundant lithiophilic sites can promote fast Li+ transport with Li+ transference number of 0.87, enabling LiFePO4 full cell with stable stripping/plating processes even at a harsh rate of 5 C. Theoretical calculations revealed that the strong interaction force between Li+ and the COF facilitated the dissolution of Li+ from the electrolyte, and the low migration barrier of 1.08 eV indicated a favorable interaction between the Li+ ions and the π-electron system.

The Importance and Discovery of Highly Connected Covalent Organic Framework Net Topologies

Furthering the field of synthetic organic chemistry from the discrete molecules regime to the extended structure regime, covalent organic frameworks (COFs) represent a new genre of crystalline porous materials featuring designability with molecular-level precision, well-defined porosity, and exceptional stability imparted by the robust covalent linkages reticulating organic molecules. The topology of COFs is a principal feature that regulates their functionality and usability for emerging technologies. Profound comprehension of network topologies and maneuvering them toward targeted applications are crucial to advancing the realm of COF research and developing novel functional materials for exciting breakthroughs. In this Perspective, we discuss the recent research pursuits contributing to the discovery of highly connected COF nets having novel topologies, assess the key challenges to achieving such network topologies, and offer insights into the current scenario and future directions.

Exploring high-connectivity three-dimensional covalent organic frameworks: topologies, structures, and emerging applications

Covalent organic frameworks (COFs) represent a highly versatile class of crystalline porous materials, formed by the deliberate assembly of organic building units into ordered two-dimensional (2D) and three-dimensional (3D) structures. Their unique combination of topological precision and tunable micro- or mesoporous architectures offers unmatched flexibility in material design. By selecting specific building units, reactive sites, and functional groups, COFs can be engineered to achieve customized skeletal, porous, and interfacial properties, opening the door to materials with optimized performance for diverse applications. Among recent advances, high-connectivity 3D COFs have emerged as a particularly exciting development, with their intricate network structures enabling unprecedented levels of structural complexity, stability, and functionality. This review provides a comprehensive overview of the synthesis strategies, topological design principles, structural characterization techniques, and emerging applications of high-connectivity 3D COFs. We explore their potential across a broad range of cutting-edge applications, including gas adsorption and separation, macromolecule adsorption, dye removal, photocatalysis, electrocatalysis, lithium-sulfur batteries, and charge transport. By examining these key areas, we aim to deepen the understanding of the intricate relationship between structure and function, guiding the rational design of next-generation COF materials. The continued advancements in this field hold immense promise for revolutionizing sectors such as energy storage, catalysis, and molecular separation, making high-connectivity 3D COFs a cornerstone for future technological innovations.

Three-Dimensional Covalent Organic Frameworks Based on Linear and Trigonal Linkers for High-Performance H2O2 Photosynthesis

The design of three-dimensional covalent organic frameworks (3D COFs) using linear and trigonal linkers remains challenging due to the difficulty in achieving a specific non-planar spatial arrangement with low-connectivity building units. Here, we report the novel 3D COFs with linear and trigonal linkers, termed TMB-COFs, exhibiting srs topology. The steric hindrance provides an additional force to alter the torsion angles of peripheral triangular units, guiding the linear unit to connect with the trigonal unit into 3D srs frameworks, rather than the more commonly observed two-dimensional (2D) hcb structures. Furthermore, we comprehensively examined the hydrogen peroxide photocatalytic production capacity of the TMB-COFs in comparison with analogous 2D COFs. The experimental results and DFT calculations demonstrate a significant enhancement in photocatalytic hydrogen peroxide production efficacy through framework regulation. This work emphasizes the steric configuration using low connectivity building units, offering a fresh perspective on the design and application of 3D COFs.

Isomeric Covalent Organic Frameworks for High-Efficiency Photocatalytic CO2 Reduction: Substituent Position Effect

The exploration of covalent organic frameworks (COFs) for high-efficiency photocatalytic CO2 reduction is urgently demanded. Herein, COF-based catalysts are constructed for the selective photoreduction of CO2 to CO via delicately designed isomeric monomers with substituent at the 4,5,9,10- positions (K) or 1,3,6,8-positions (A) of pyrene knots. The distinct substituted regions significantly affect the planarity of pyrene knots, resulting in COFs with different microstructures and photocatalytic activities. While employing a 5 W LED white-light as the light source, the single atomic Co contained A-Py-Bpy-COF-Co showcased a moderate CO evolution rate of 2174.4 µmol g-1 h-1. In sharp contrast, K-Py-Bpy-COF-Co reveals a considerable CO photo-reduction rate of 12 476.4 µmol g-1 h-1 (5.7 times higher than A-Py-Bpy-COF) with a selectivity up to 93.3%. Remarkably, the excellent photocatalytic activity of K-Py-Bpy-COF-Co can be maintained for at least 5 cycles without obvious decay. The distinct photocatalytic properties of the two isomeric COFs can be attributed to the larger steric-hindrance of K-Py-4CHO which enlarges the interlayer distances to inhibit exciton quenching and electron-richer nature of monatomic Co in K-Py-Bpy-COF-Co. This work provides a new protocol to explore COFs with boosted photocatalytic performance via isomeric design from refined modulation of reported COFs.

Photons, Excitons, and Electrons in Covalent Organic Frameworks

Covalent organic frameworks (COFs) are created by the condensation of molecular building blocks and nodes to form two-dimensional (2D) or three-dimensional (3D) crystalline frameworks. The diversity of molecular building blocks with different properties and functionalities and the large number of possible framework topologies open a vast space of possible well-defined porous architectures. Besides more classical applications of porous materials such as molecular absorption, separation, and catalytic conversions, interest in the optoelectronic properties of COFs has recently increased considerably. The electronic properties of both the molecular building blocks and their linkage chemistry can be controlled to tune photon absorption and emission, to create excitons and charge carriers, and to use these charge carriers in different applications such as photocatalysis, luminescence, chemical sensing, and photovoltaics. In this Perspective, we will discuss the relationship between the structural features of COFs and their optoelectronic properties, starting with the building blocks and their chemical connectivity, layer stacking in 2D COFs, control over defects and morphology including thin film synthesis, exploring the theoretical modeling of structural, electronic, and dynamic features of COFs, and discussing recent intriguing applications with a focus on photocatalysis and photoelectrochemistry. We conclude with some remarks about present challenges and future prospects of this powerful architectural paradigm.

A comprehensive review of covalent organic frameworks (COFs) and their derivatives in environmental pollution control

Covalent organic frameworks (COFs) have gained considerable attention due to their design possibilities as the molecular organic building blocks that can stack in an atomically precise spatial arrangement. Since the inception of COFs in 2005, there has been a continuous expansion in the product range of COFs and their derivatives. This expansion has led to the evolution of three-dimensional structures and various synthetic routes, propelling the field towards large-scale preparation of COFs and their derivatives. This review will offer a holistic analysis and comparison of the spatial structure and synthesis techniques of COFs and their derivatives. The conventional methods of COF synthesis (i.e., ultrasonic chemical, microwave, and solvothermal) are discussed alongside the synthesis strategies of new COFs and their derivatives. Furthermore, the applications of COFs and their derived materials are demonstrated in air, water, and soil pollution management such as gas capture, catalytic conversion, adsorption, and pollutant removal. Finally, this review highlights the current challenges and prospects for large-scale preparation and application of new COFs and the derived materials. In line with the United Nations Sustainable Development Goals (SDGs) and the needs of digital-enabled technologies (AI and machine learning), this review will encompass the future technical trends for COFs in environmental pollution control.

Two-dimensional carbazole-based COFs for high-performance lithium-sulfur batteries

Carbazole-based COFs were synthesized and applied as the sulfur-host in cathode materials for lithium-sulfur batteries (LSBs), which effectively mitigate the shuttle effect of lithium polysulfides. A high initial capacity of 1232 mAh g-1 at 0.1C is achieved, while also showing excellent capacity retention and stability in cyclic experiments. This work highlights the potential application of carbazole-based COFs for LSBs.

3D Covalent Organic Frameworks with 16-Connectivity for Photocatalytic C(sp3)-C(sp2) Cross-Coupling

The connectivity (valency) of building blocks for constructing 3D covalent organic frameworks (COFs) has long been limited to 4, 6, 8, and 12. Developing a higher connectivity remains a great challenge in the field of COF structural design. Herein, this work reports a hierarchical expansion strategy for making 16-connected building blocks to construct 3D COFs with sqc topology. The [16 + 2] construction achieved by condensation between a 16-connected carbazolyl dicyanobenzene-based building block (CzTPN) and linear diamino linkers (BD or Bpy) affords two 3D COFs (named CzBD COF and CzBpy COF). Furthermore, attributed to the well-organized donor-acceptor (D-A) heterojunction, the Ni chelated CzBpy COF (Ni@CzBpy COF) exhibits excellent performance for photoredox/Ni dual catalytic C(sp3)-C(sp2) cross-coupling of alkyltrifluoroborates with aryl halides, achieving a maximum 98% conversion and 94% yield for various substrates. This work developed the first case of high-connectivity COFs bearing 16-connected units, which is the highest connectivity reported until now, and achieved efficient photocatalysis applications, thus greatly enriching the possibilities of COFs.

Manipulating Orbital Hybridization of CoSe2 by S Doping for the Highly Active Catalytic Effect of Lithium-Sulfur Batteries

In recent years, various transition metal compounds have been extensively studied to deal with the problems of slow reaction kinetics and the shuttle effect of lithium-sulfur (Li-S) batteries. Nevertheless, their catalytic performance still needs to be further improved by enhancing intrinsic catalytic activity and enriching active sites. Doping is an effective means to boost the catalytic performance through adjusting the electron structure of the catalysts. Herein, the electron structure of CoSe2 is adjusted by doping P, S with different p electron numbers and electronegativity. After S doping (S-CoSe2), the content of Co2+ increases, and charge is redistributed. Furthermore, more electrons are transferred between Li2S4/Li2S and S-CoSe2, and optimal Co-S bonds are formed between them with optimized d-p orbital hybridization, making the bonds of Li2S4/Li2S the longest and easy to break and decompose. Consequently, the Li-S batteries with the S-CoSe2-modified separator achieve improved rate performance and cycling performance, benefiting from the better bidirectional catalytic activity. This work will provide reference for the selection of the anion doping element to enhance the catalytic effect of transition metal compounds.

Cationic covalent organic framework nanosheets as the coating layer of commercial separator for high-efficiency lithium-sulfur batteries

Ion-selective separators, are crucial and in high demand for maximizing the performance of lithium-sulfur (Li-S) batteries, which can conduct lithium ions while efficiently blocking polysulfides. However, commercial separators cannot effectively block the shuttle of polysulfides after multiple cycles due to their large porosity and easy dissolution, resulting in a reduced battery life. Herein, a covalent organic framework nanosheets (CON) ion-coated separator is prepared on the commercial separator. Due to the smaller pore size of CON-TFSI compared to polysulfides, the CON-TFSI modified separator can effectively block the polysulfide from migrating across the separator. By incorporating this innovative functional layer, Li-S batteries demonstrate outstanding performance. In a Li-S battery featuring a sulfur loading of 0.6 mg/cm2, it attains an initial discharge specific capacity of up to 891.9 mA h g-1, and exhibits the capacity retention of 54.6 % after 500 cycles at a current density of 0.2 C. This work offers a fresh perspective on the advancement of high-performance membranes for Li-S batteries.

Porous Organic Polymers as Active Electrode Materials for Energy Storage Applications

Eco-friendly and efficient energy production and storage technologies are highly demanded to address the environmental and energy crises. Porous organic polymers (POPs) are a class of lightweight porous network materials covalently linked by organic building blocks, possessing high surface areas, tunable pores, and designable components and structures. Due to their unique structural and compositional advantages, POPs have recently emerged as promising electrode materials for energy storage devices, particularly in the realm of supercapacitors and ion batteries. In this work, a comprehensive overview of recent progress and applications of POPs as electrode materials in energy storage devices, including the structural features and synthesis strategies of various POPs, as well as their applications in supercapacitors, lithium batteries, sodium batteries, and potassium batteries are provided. Finally, insights are provided into the future research directions of POPs in electrochemical energy storage technologies. It is anticipated that this work can provide readers with a comprehensive background on the design of POPs-based electrode materials and ignite more research in the development of next-generation energy storage devices.

Covalent Organic Framework-Based Materials for Advanced Lithium Metal Batteries

Lithium metal batteries (LMBs), with high energy densities, are strong contenders for the next generation of energy storage systems. Nevertheless, the unregulated growth of lithium dendrites and the unstable solid electrolyte interphase (SEI) significantly hamper their cycling efficiency and raise serious safety concerns, rendering LMBs unfeasible for real-world implementation. Covalent organic frameworks (COFs) and their derivatives have emerged as multifunctional materials with significant potential for addressing the inherent problems of the anode electrode of the lithium metal. This potential stems from their abundant metal-affine functional groups, internal channels, and widely tunable architecture. The original COFs, their derivatives, and COF-based composites can effectively guide the uniform deposition of lithium ions by enhancing conductivity, transport efficiency, and mechanical strength, thereby mitigating the issue of lithium dendrite growth. This review provides a comprehensive analysis of COF-based and derived materials employed for mitigating the challenges posed by lithium dendrites in LMB. Additionally, we present prospects and recommendations for the design and engineering of materials and architectures that can render LMBs feasible for practical applications.

Unprecedented POSS-Linked 3D Covalent Organic Frameworks with 2-Fold Interpenetrated scu or sqc Topology Regulated by Porphyrin Center for Photocatalytic CO2 Reduction

The synthesis and characterization of porphyrin center regulated three-dimensional covalent organic frameworks (COFs) with 2-fold interpenetrated scu or sqc topology have been investigated. These COFs exhibit unique structural features and properties, making them promising candidates for photocatalytic applications in CO2 reduction and artemisinin synthesis. The porphyrin center serves as an anchor for metal ions, allowing precise control over structures and functions of the frameworks. Furthermore, the metal coordination within the framework imparts desirable catalytic properties, enabling their potential use in photocatalytic reactions. Overall, these porphyrin center regulated metal-controlled COFs offer exciting opportunities for the development of advanced materials with tailored functionalities.

Covalent organic frameworks and their composites for rechargeable batteries

Covalent organic frameworks (COFs), characterized by well-ordered pores, large specific surface area, good stability, high precision, and flexible design, are a promising material for batteries and have received extensive attention from researchers in recent years. Compared with inorganic materials, COFs can construct elastic frameworks with better structural stability, and their chemical compositions and structures can be precisely adjusted and functionalized at the molecular level, providing an open pathway for the convenient transfer of ions. In this review, the energy storage mechanism and unique superiority of COFs and COF composites as electrodes, separators and electrolytes for rechargeable batteries are discussed in detail. Special emphasis is placed on the relationship between the establishment of COF structures and their electrochemical performance in different batteries. Finally, this review summarizes the challenges and prospects of COFs and COF composites in battery equipment.

3D Covalent Organic Frameworks from Design, Synthesis to Applications in Optoelectronics

Covalent organic frameworks (COFs), a new class of crystalline materials connected by covalent bonds, have been developed rapidly in the past decades. However, the research on COFs is mainly focused on two-dimensional (2D) COFs, and the research on three-dimensional (3D) COFs is still in the initial stage. In 2D COFs, the covalent bonds exist only in the 2D flakes and can form 1D channels, which hinder the charge transport to some extent. In contrast, 3D COFs have a more complex pore structure and thus exhibit higher specific surface area and richer active sites, which greatly enhance the 3D charge carrier transport. Therefore, compared to 2D COFs, 3D COFs have stronger applicability in energy storage and conversion, sensing, and optoelectronics. In this review, it is first introduced the design principles for 3D COFs, and in particular summarize the development of conjugated building blocks in 3D COFs, with a special focus on their application in optoelectronics. Subsequently, the preparation of 3D COF powders and thin films and methods to improve the stability and functionalization of 3D COFs are summarized. Moreover, the applications of 3D COFs in electronics are outlined. Finally, conclusions and future research directions for 3D COFs are presented.

Topological Analysis and Structural Determination of 3D Covalent Organic Frameworks

3D covalent organic frameworks (3D COFs) constitute a new type of crystalline materials that consist of a range of porous structures with numerous applications in the fields of adsorption, separation, and catalysis. However, because of the complexity of the three-periodic net structure, it is desirable to develop a thorough structural comprehension, along with a means to precisely determine the actual structure. Indeed, such advancements would considerably contribute to the rational design and application of 3D COFs. In this review, the reported topologies of 3D COFs are introduced and categorized according to the configurations of their building blocks, and a comprehensive overview of diffraction-based structural determination methods is provided. The current challenges and future prospects for these materials will also be discussed.

Rechargeable Metal-Sulfur Batteries: Key Materials to Mechanisms

Rechargeable metal-sulfur batteries are considered promising candidates for energy storage due to their high energy density along with high natural abundance and low cost of raw materials. However, they could not yet be practically implemented due to several key challenges: (i) poor conductivity of sulfur and the discharge product metal sulfide, causing sluggish redox kinetics, (ii) polysulfide shuttling, and (iii) parasitic side reactions between the electrolyte and the metal anode. To overcome these obstacles, numerous strategies have been explored, including modifications to the cathode, anode, electrolyte, and binder. In this review, the fundamental principles and challenges of metal-sulfur batteries are first discussed. Second, the latest research on metal-sulfur batteries is presented and discussed, covering their material design, synthesis methods, and electrochemical performances. Third, emerging advanced characterization techniques that reveal the working mechanisms of metal-sulfur batteries are highlighted. Finally, the possible future research directions for the practical applications of metal-sulfur batteries are discussed. This comprehensive review aims to provide experimental strategies and theoretical guidance for designing and understanding the intricacies of metal-sulfur batteries; thus, it can illuminate promising pathways for progressing high-energy-density metal-sulfur battery systems.

12 Connecting Sites Linked Three-dimensional Covalent Organic Frameworks with Intrinsic Non-interpenetrated shp Topology for Photocatalytic H2O2 Synthesis

Developing high connectivity (>8) three-dimensional (3D) covalent organic frameworks (COFs) towards new topologies and functions remains a great challenge owing to the difficulty in getting high connectivity organic building blocks. This however represents the most important step towards promoting the diversity of COFs due to the still limited dynamic covalent bonds available for constructing COFs at this stage. Herein, highly connected phthalocyanine-based (Pc-based) 3D COFs MPc-THHI-COFs (M=H2, Ni) were afforded from the reaction between 2,3,9,10,16,17,23,24-octacarboxyphthalocyanine M(TAPc) (M=H2, Ni) and 5,5',5'',5''',5'''',5'''''-(triphenylene-2,3,6,7,10,11-hexayl)hexa(isophthalohydrazide) (THHI) with 12 connecting sites. Powder X-ray diffraction analysis together with theoretical simulations and transmission electron microscopy reveals their crystalline nature with an unprecedented non-interpenetrated shp topology. Experimental and theoretical investigations disclose the broadened visible light absorption range and narrow optical band gap of MPc-THHI-COFs. This in combination with their 3D nanochannels endows them with efficient photocatalysis performance for H2O2 generation from O2 and H2O via 2e- oxygen reduction reaction and 2e- water oxidation reaction under visible-light irradiation (λ >400 nm). This work provides valuable result for the development of high connectivity functional COFs towards diverse application potentials.

Metal-Coordinated Covalent Organic Frameworks as Advanced Bifunctional Hosts for Both Sulfur Cathodes and Lithium Anodes in Lithium-Sulfur Batteries

The shuttling of polysulfides on the cathode and the uncontrollable growth of lithium dendrites on the anode have restricted the practical application of lithium-sulfur (Li-S) batteries. In this study, a metal-coordinated 3D covalent organic framework (COF) with a homogeneous distribution of nickel-bis(dithiolene) and N-rich triazine centers (namely, NiS4-TAPT) was designed and synthesized, which can serve as bifunctional hosts for both sulfur cathodes and lithium anodes in Li-S batteries. The abundant Ni centers and N-sites in NiS4-TAPT can greatly enhance the adsorption and conversion of the polysulfides. Meanwhile, the presence of Ni-bis(dithiolene) centers enables uniform Li nucleation at the Li anode, thereby suppressing the growth of Li dendrites. This work demonstrated the effectiveness of integrating catalytic and adsorption sites to optimize the chemical interactions between host materials and redox-active intermediates, potentially facilitating the rational design of metal-coordinated COF materials for high-performance secondary batteries.

Accessible Tetrathiafulvalene Moieties in a 3D Covalent Organic Framework for Enhanced Near-Infrared Photo-Thermal Conversion and Photo-Electrical Response

Redox-active tetrathiafulvalene (TTF)-based covalent organic frameworks (COFs) exhibit distinctive electrochemical and photoelectrical properties, but their prevalent two-dimensional (2D) structure with densely packed TTF moieties limits the accessibility of redox center and constrains their potential applications. To overcome this challenge, an 8-connected TTF linker (TTF-8CHO) is designed as a new building block for the construction of three-dimensional (3D) COFs. This approach led to the successful synthesis of a 3D COF with the bcu topology, designated as TTF-8CHO-COF. In comparison to its 2D counterpart employing a 4-connected TTF linker, the 3D COF design enhances access to redox sites, facilitating controlled oxidation by I2 or Au3+ to tune physical properties. When irradiated with a 0.7 W cm-2 808 nm laser, the oxidized 3D COF samples (I X - ${\mathrm{I}}_{\mathrm{X}}^{-}$ @TTF-8CHO-COF and Au NPs@TTF-8CHO-COF) demonstrated rapid temperature increases of 239.3 and 146.1 °C, respectively, which surpassed those of pristine 3D COF (65.6 °C) and the 2D COF counterpart (6.4 °C increment after I2 treatment). Furthermore, the oxidation of the 3D COF heightened its photoelectrical responsiveness under 808 nm laser irradiation. This augmentation in photothermal and photoelectrical response can be attributed to the higher concentration of TTF·+ radicals generated through the oxidation of well-exposed TTF moieties.

Single-atom platinum with asymmetric coordination environment on fully conjugated covalent organic framework for efficient electrocatalysis

Two-dimensional (2D) covalent organic frameworks (COFs) and their derivatives have been widely applied as electrocatalysts owing to their unique nanoscale pore configurations, stable periodic structures, abundant coordination sites and high surface area. This work aims to construct a non-thermodynamically stable Pt-N2 coordination active site by electrochemically modifying platinum (Pt) single atoms into a fully conjugated 2D COF as conductive agent-free and pyrolysis-free electrocatalyst for the hydrogen evolution reaction (HER). In addition to maximizing atomic utilization, single-atom catalysts with definite structures can be used to investigate catalytic mechanisms and structure-activity relationships. In this work, in-situ characterizations and theoretical calculations reveal that a nitrogen-rich graphene analogue COF not only exhibits a favorable metal-support effect for Pt, adjusting the binding energy between Pt sites to H* intermediates by forming unique Pt-N2 instead of the typical Pt-N4 coordination environment, but also enhances electron transport ability and structural stability, showing both conductivity and stability in acidic environments.

Covalent Organic Frameworks as Electrode Materials for Alkali Metal-ion Batteries

Covalent organic frameworks (COFs) are a class of porous crystalline polymeric materials constructed by linking organic small molecules through covalent bonds. COFs have the advantages of strong covalent bond network, adjustable pore structure, large specific surface area and excellent thermal stability, and have broad application prospects in various fields. Based on these advantages, rational COFs design strategies such as the introduction of active sites, construction of conjugated structures, and carbon material composite, etc. can effectively improve the conductivity and stability of the electrode materials in the field of batteries. This paper introduces the latest research results of high-performance COFs electrode materials in alkali metal-ion batteries (LIBs, SIBs, PIBs and LSBs) and other advanced batteries. The current challenges and future design directions of COFs-based electrode are discussed. It provides useful insights for the design of novel COFs structures and the development of high-performance alkali metal-ion batteries.

Synthesis of 12-Connected Three-Dimensional Covalent Organic Framework with lnj Topology

The structural exploration of three-dimensional covalent organic frameworks (3D COFs) is of great significance to the development of COF materials. Different from structurally diverse MOFs, which have a variety of connectivity (3-24), now the valency of 3D COFs is limited to only 4, 6, and 8. Therefore, the exploration of organic building blocks with higher connectivity is a necessary path to broaden the scope of 3D COF structures. Herein, for the first time, we have designed and synthesized a 12-connected triptycene-based precursor (triptycene-12-CHO) with 12 symmetrical distributions of aldehyde groups, which is also the highest valency reported until now. Based on this unique 12-connected structure, we have successfully prepared a novel 3D COF with lnj topology (termed 3D-lnj-COF). The as-synthesized 3D COF exhibits honeycomb main pores and permanent porosity with a Brunauer-Emmett-Teller surface area of 1159.6 m2 g-1. This work not only provides a strategy for synthesizing precursors with a high connectivity but also provides inspiration for enriching the variety of 3D COFs.

Unlocking Synthesis of Polyhedral Oligomeric Silsesquioxane-Based Three-Dimensional Polycubane Covalent Organic Frameworks

Reticular chemistry effectively yields porous structures with distinct topological lattices for a broad range of applications. Polyhedral oligomeric silsesquioxane (POSS)-based octatopic building blocks with a rare Oh symmetric configuration and attracting inorganic features have great potential for creating three-dimensional (3D) covalent organic frameworks (COFs) with new topologies. However, the intrinsic flexibility and intensive motion of cubane-type POSS molecules make the construction of 3D regular frameworks challenging. Herein, by fastening three or four POSS cores with per aromatic rigid linker from rational steric directions, we successfully developed serial crystalline 3D COFs with unpresented "the" and scu topologies. Both the experimental and theoretical results proved the formation of target 3D POSS-based COFs. The resultant hybrid networks with designable chemical skeletons and high surface areas maintain the superiorities of both the inorganic and organic components, such as their high compatibility with inorganic salts, abundant periodic electroactive sites, excellent thermal stability, and open multilevel nanochannels. Consequently, the polycubane COFs could serve as outstanding solid electrolytes with a high ionic conductivity of 1.23 × 10-4 S cm-1 and a lithium-ion transference number of 0.86 at room temperature. This work offers a pathway to generate ordered lattices with multiconnected flexible cube motifs and enrich the topologies of 3D COFs for potential applications.

Hydrophobic Trinuclear Copper Cluster-Containing Organic Framework for Synergetic Electrocatalytic Synthesis of Amino Acids

Electrocatalytic synthesis of amino acids provides a promising green and efficient pathway to manufacture the basic substances of life. Herein, reaction of 2,5-perfluroalkyl-terepthalohydrazide and tris(4-µ2 -O-carboxaldehyde-pyrazolato-N, N')-tricopper affords a crystalline trinuclear copper cluster-containing organic framework, named F-Cu3 -OF. Incorporation of abundant hydrophobic perfluroalkyl groups inside the channels of F-Cu3 -OF is revealed to successfully suppress the hydrogen evolution reaction via preventing H+ cation with large polarity from the framework of F-Cu3 -OF and in turn increasing the adsorption of other substrates with relatively small polarity like NO3 - and keto acids on the active sites. The copper atoms with short distance in the trinuclear copper clusters of F-Cu3 -OF enable simultaneous activization of NO3 - and keto acids, facilitating the following synergistic and efficient C─N coupling on the basis of in situ spectroscopic investigations together with theoretical calculation. Combination of these effects leads to efficient electroproduction of various amino acids including glycine, alanine, leucine, valine, and phenylalanine from NO3 - and keto acids with a Faraday efficiency of 42%-71% and a yield of 187-957 µmol cm-2 h-1 , representing the thus far best performance. This work shall be helpful for developing economical, eco-friendly, and high-efficiency strategy for the production of amino acids and other life substances.

Size Effect for Inhibiting Polysulfides Shuttle in Lithium-Sulfur Batteries

It is undeniable that the dissolution of polysulfides is beneficial in speeding up the conversion rate of sulfur in electrochemical reactions. But it also brings the bothersome "shuttle effect". Therefore, if polysulfides can be retained on the cathode side, the efficient utilization of the polysulfides can be guaranteed to achieve the excellent performance of lithium-sulfur batteries. Based on this idea, considerable methods have been developed to inhibit the shuttling of polysulfides. It is necessary to emphasize that no matter which method is used, the solvation mechanism, and existence forms of polysulfides are essential to analyze. Especially, it is important to clarify the sizes of different forms of polysulfides when using the size effect to inhibit the shuttling of polysulfides. In this review, a comprehensive summary and in-depth discussion of the solvation mechanism, the existing forms of polysulfides, and the influencing factors affecting polysulfides species are presented. Meanwhile, the size of diverse polysulfide species is sorted out for the first time. Depending on the size of polysulfides, tactics of using size effect in cathode, separator, and interlayer parts are elaborated. Finally, a design idea of materials pore size is proposed to satisfy the use of size effect to inhibit polysulfides shuttle.

Single Cobalt Ion-Immobilized Covalent Organic Framework for Lithium-Sulfur Batteries with Enhanced Rate Capabilities

Covalent organic frameworks (COFs) are notable for their remarkable structure, function designability, and tailorability, as well as stability, and the introduction of "open metal sites" ensures the efficient binding of small molecules and activation of substrates for heterogeneous catalysis and energy storage. Herein, we use the postsynthetic metal sites to catalyze polysulfide conversion and to boost the binding affinity to active matter for lithium-sulfur batteries (LSBs). A dual-pore COF, USTB-27, with hxl topology has been successfully assembled from the imine chemical reaction between 2,3,8,9,14,15-hexa(4-formylphenyl)diquinoxalino [2,3-a:2',3'-c]phenazine and [2,2'-bipyridine]-5,5'-diamine. The chelating nitrogen sites of both modules are able to postsynthetically functionalize with single cobalt sites to generate USTB-27-Co. The discharge capacity of the sulfur-loaded S@USTB-27-Co composite in a LSB is 1063, 945, 836, 765, 696, and 644 mA h g-1 at current densities of 0.1, 0.2, 0.5, 1.0, 2.0, and 5.0 C, respectively, much superior to that of non-cobalt-functionalized species S@USTB-27. Following the increased current densities, the rate performance of S@USTB-27-Co is much better than that of S@USTB-27. In particular, the capacity retention at 5.0 C has a magnificent increase from 19% for the latter species to 61% for the former one. Moreover, S@USTB-27-Co exhibits a higher specific capacity of 543 mA h g-1 than that of S@USTB-27 (402 mA h g-1) at a current density of 1.0 C after electrochemical cycling for 500 runs. This work illustrates the "open metal sites" strategy to engineer the active chemical component conversion in COF channels as well as their binding strength for specific applications.

Three-dimensional covalent organic frameworks with nia nets for efficient separation of benzene/cyclohexane mixtures

The synthesis of three-dimensional covalent organic frameworks with highly connected building blocks presents a significant challenge. In this study, we report two 3D COFs with the nia topology, named JUC-641 and JUC-642, by introducing planar hexagonal and triangular prism nodes. Notably, our adsorption studies and breakthrough experiments reveal that both COFs exhibit exceptional separation capabilities, surpassing previously reported 3D COFs and most porous organic polymers, with a separation factor of up to 2.02 for benzene and cyclohexane. Additionally, dispersion-corrected density functional theory analysis suggests that the good performance of these 3D COFs can be attributed to the incorporation of highly aromatic building blocks and the presence of extensive pore structures. Consequently, this research not only expands the diversity of COFs but also highlights the potential of functional COF materials as promising candidates for environmentally-friendly separation applications.

Covalent Organic Frameworks: Their Composites and Derivatives for Rechargeable Metal-Ion Batteries

Covalent organic frameworks (COFs) have attracted considerable interest in the field of rechargeable batteries owing to their three-dimensional (3D) varied pore sizes, inerratic porous structures, abundant redox-active sites, and customizable structure-adjustable frameworks. In the context of metal-ion batteries, these materials play a vital role in electrode materials, effectively addressing critical issues such as low ionic conductivity, limited specific capacity, and unstable structural integrity. However, the electrochemical characteristics of the developed COFs still fall short of practical battery requirements due to inherent issues such as low electronic conductivity, the tradeoff between capacity and redox potential, and unfavorable micromorphology. This review provides a comprehensive overview of the recent advancements in the application of COFs, COF-based composites, and their derivatives in rechargeable metal-ion batteries, including lithium-ion, lithium-sulfur, sodium-ion, sodium-sulfur, potassium-ion, zinc-ion, and other multivalent metal-ion batteries. The operational mechanisms of COFs, COF-based composites, and their derivatives in rechargeable batteries are elucidated, along with the strategies implemented to enhance the electrochemical properties and broaden the range of their applications.

Enhanced Electron Delocalization within Coherent Nano-Heterocrystal Ensembles for Optimizing Polysulfide Conversion in High-Energy-Density Li-S Batteries

Commercialization of high energy density Lithium-Sulfur (Li-S) batteries is impeded by challenges such as polysulfide shuttling, sluggish reaction kinetics, and limited Li+ transport. Herein, a jigsaw-inspired catalyst design strategy that involves in situ assembly of coherent nano-heterocrystal ensembles (CNEs) to stabilize high-activity crystal facets, enhance electron delocalization, and reduce associated energy barriers is proposed. On the catalyst surface, the stabilized high-activity facets induce polysulfide aggregation. Simultaneously, the surrounded surface facets with enhanced activity promote Li2 S deposition and Li+ diffusion, synergistically facilitating continuous and efficient sulfur redox. Experimental and DFT computations results reveal that the dual-component hetero-facet design alters the coordination of Nb atoms, enabling the redistribution of 3D orbital electrons at the Nb center and promoting d-p hybridization with sulfur. The CNE, based on energy level gradient and lattice matching, endows maximum electron transfer to catalysts and establishes smooth pathways for ion diffusion. Encouragingly, the NbN-NbC-based pouch battery delivers a Weight energy density of 357 Wh kg-1 , thereby demonstrating the practical application value of CNEs. This work unveils a novel paradigm for designing high-performance catalysts, which has the potential to shape future research on electrocatalysts for energy storage applications.

Organic electrodes based on redox-active covalent organic frameworks for lithium batteries

Electroactive organic materials have received much attention as alternative electrodes for metal-ion batteries due to their high theoretical capacity, resource availability, and environmental friendliness. In particular, redox-active covalent organic frameworks (COFs) have recently emerged as promising electrodes due to their tunable electrochemical properties, insolubility in electrolytes, and structural versatility. In this Highlight, we review some recent strategies to improve the energy density and power density of COF electrodes for lithium batteries from the perspective of molecular design and electrode optimisation. Some other aspects such as stability and scalability are also discussed. Finally, the main challenges to improve their performance and future prospects for COF-based organic batteries are highlighted.

Multicomponent Synthesis of Imidazole-Linked Fully Conjugated 3D Covalent Organic Framework for Efficient Electrochemical Hydrogen Peroxide Production

The semiconducting properties and applications of three dimensional (3D) covalent organic frameworks (COFs) are greatly hampered because of their long-ranged non-conjugated skeletons and relatively unstable linkages. Here, a robust imidazole-linked fully conjugated 3D covalent organic framework (BUCT-COF-7) is synthesized through the one-pot multicomponent Debus-Radziszewski reaction of the saddle-shaped aldehyde-substituted cyclooctatetrathiophene, pyrene-4,5,9,10-tetraone, and ammonium acetate. The semiconducting BUCT-COF-7, as a metal-free catalyst, shows excellent two electron oxygen reduction reaction (ORR) activity in alkaline medium with high hydrogen peroxide (H2 O2 ) selectivity of 83.4 %. When the BUCT-COF-7 as cathode catalyst is assembled into the electrolyzer, the devices showed high electrochemical production rate of H2 O2 up to 326.9 mmol g-1 h-1 . The accumulative amount of H2 O2 could totally degrade the dye methylene blue via Fenton reaction for wastewater treatment. This is the first report about intrinsic 3D COFs for efficient electrochemical synthesis of H2 O2 , revealing the promising applications of fully conjugated 3D COFs in the environment-related field.

Recent Progress on Phase Engineering of Nanomaterials

As a key structural parameter, phase depicts the arrangement of atoms in materials. Normally, a nanomaterial exists in its thermodynamically stable crystal phase. With the development of nanotechnology, nanomaterials with unconventional crystal phases, which rarely exist in their bulk counterparts, or amorphous phase have been prepared using carefully controlled reaction conditions. Together these methods are beginning to enable phase engineering of nanomaterials (PEN), i.e., the synthesis of nanomaterials with unconventional phases and the transformation between different phases, to obtain desired properties and functions. This Review summarizes the research progress in the field of PEN. First, we present representative strategies for the direct synthesis of unconventional phases and modulation of phase transformation in diverse kinds of nanomaterials. We cover the synthesis of nanomaterials ranging from metal nanostructures such as Au, Ag, Cu, Pd, and Ru, and their alloys; metal oxides, borides, and carbides; to transition metal dichalcogenides (TMDs) and 2D layered materials. We review synthesis and growth methods ranging from wet-chemical reduction and seed-mediated epitaxial growth to chemical vapor deposition (CVD), high pressure phase transformation, and electron and ion-beam irradiation. After that, we summarize the significant influence of phase on the various properties of unconventional-phase nanomaterials. We also discuss the potential applications of the developed unconventional-phase nanomaterials in different areas including catalysis, electrochemical energy storage (batteries and supercapacitors), solar cells, optoelectronics, and sensing. Finally, we discuss existing challenges and future research directions in PEN.

Aggregation behaviour of pyrene-based luminescent materials, from molecular design and optical properties to application

Molecular aggregates are self-assembled from multiple molecules via weak intermolecular interactions, and new chemical and physical properties can emerge compared to their individual molecule. With the development of aggregate science, much research has focused on the study of the luminescence behaviour of aggregates rather than single molecules. Pyrene as a classical fluorophore has attracted great attention due to its diverse luminescence behavior depending on the solution state, molecular packing pattern as well as morphology, resulting in wide potential applications. For example, pyrene prefers to emit monomer emission in dilute solution but tends to form a dimer via π-π stacking in the aggregation state, resulting in red-shifted emission with quenched fluorescence and quantum yield. Over the past two decades, much effort has been devoted to developing novel pyrene-based fluorescent molecules and determining the luminescence mechanism for potential applications. Since the concept of "aggregation-induced emission (AIE)" was proposed by Tang et al. in 2001, aggregate science has been established, and the aggregated luminescence behaviour of pyrene-based materials has been extensively investigated. New pyrene-based emitters have been designed and synthesized not only to investigate the relationships between the molecular structure and properties and advanced applications but also to examine the effect of the aggregate morphology on their optical and electronic properties. Indeed, new aggregated pyrene-based molecules have emerged with unique properties, such as circularly polarized luminescence, excellent fluorescence and phosphorescence and electroluminescence, ultra-high mobility, etc. These properties are independent of their molecular constituents and allow for a number of cutting-edge technological applications, such as chemosensors, organic light-emitting diodes, organic field effect transistors, organic solar cells, Li-batteries, etc. Reviews published to-date have mainly concentrated on summarizing the molecular design and multi-functional applications of pyrene-based fluorophores, whereas the aggregation behaviour of pyrene-based luminescent materials has received very little attention. The majority of the multi-functional applications of pyrene molecules are not only closely related to their molecular structures, but also to the packing model they adopt in the aggregated state. In this review, we will summarize the intriguing optoelectronic properties of pyrene-based luminescent materials boosted by aggregation behaviour, and systematically establish the relationship between the molecular structure, aggregation states, and optoelectronic properties. This review will provide a new perspective for understanding the luminescence and electronic transition mechanism of pyrene-based materials and will facilitate further development of pyrene chemistry.

Covalent organic frameworks for CO2 capture: from laboratory curiosity to industry implementation

CO2 concentration in the atmosphere has increased by about 40% since the 1960s. Among various technologies available for carbon capture, adsorption and membrane processes have been receiving tremendous attention due to their potential to capture CO2 at low costs. The kernel for such processes is the sorbent and membrane materials, and tremendous progress has been made in designing and fabricating novel porous materials for carbon capture. Covalent organic frameworks (COFs), a class of porous crystalline materials, are promising sorbents for CO2 capture due to their high surface area, low density, controllable pore size and structure, and preferable stabilities. However, the absence of synergistic developments between materials and engineering processes hinders achieving the qualitative leap for net-zero emissions. Considering the lack of a timely review on the combination of state-of-the-art COFs and engineering processes, in this Tutorial Review, we emphasize the developments of COFs for meeting the challenges of carbon capture and disclose the strategies of fabricating COFs for realizing industrial implementation. Moreover, this review presents a detailed and basic description of the engineering processes and industrial status of carbon capture. It highlights the importance of machine learning in integrating simulations of molecular and engineering levels. We aim to stimulate both academia and industry communities for joined efforts in bringing COFs to practical carbon capture.