Redox Donor-Acceptor Conjugated Microporous Polymers as Ultralong-Lived Organic Anodes for Rechargeable Air Batteries

Anthraquinones-based photocatalysis: A comprehensive review

In recent years, there has been significant interest in photocatalytic technologies utilizing semiconductors and photosensitizers responsive to solar light, owing to their potential for energy and environmental applications. Current efforts are focused on enhancing existing photocatalysts and developing new ones tailored for environmental uses. Anthraquinones (AQs) serve as redox-active electron transfer mediators and photochemically active organic photosensitizers, effectively addressing common issues such as low light utilization and carrier separation efficiency found in conventional semiconductors. AQs offer advantages such as abundant raw materials, controlled preparation, excellent electron transfer capabilities, and photosensitivity, with applications spanning the energy, medical, and environmental sectors. Despite their utility, comprehensive reviews on AQs-based photocatalytic systems in environmental contexts are lacking. In this review, we thoroughly describe the photochemical properties of AQs and their potential applications in photocatalysis, particularly in addressing key environmental challenges like clean energy production, antibacterial action, and pollutant degradation. However, AQs face limitations in practical photocatalytic applications due to their low electrical conductivity and solubility-related secondary contamination. To mitigate these issues, the design and synthesis of graphene-immobilized AQs are highlighted as a solution to enhance practical photocatalytic applications. Additionally, future research directions are proposed to deepen the understanding of AQs' theoretical mechanisms and to provide practical applications for wastewater treatment. This review aims to facilitate mechanistic studies and practical applications of AQs-based photocatalytic technologies and to improve understanding of these technologies.

Extending the π-Conjugation of a Donor-Acceptor Covalent Organic Framework for High-Rate and High-Capacity Lithium-Ion Batteries

Realizing high-rate and high-capacity features of Lihium-organic batteries is essential for their practical use but remains a big challenge, which is due to the instrinsic poor conductivity, limited redox kinetics and low utility of organic electrode mateials. This work presents a well-designed donor-acceptor Covalent Organic Framework (COFs) with extended conjugation, mesoscale porosity, and dual redox-active centers to promote fast charge transfer and multi-electron processes. As anticipated, the prepared cathode with benzo [1,2-b:3,4-b':5,6-b''] trithiophene (BTT) as p-type and pyrene-4,5,9,10-tetraone (PTO) as n-type material (BTT-PTO-COF) delivers impressive specific capacity (218 mAh g-1 at 0.2 A g-1 in ether-based electrolyte and 275 mAh g-1 at 0.2 A g-1 in carbonate-based electrolyte) and outstanding rate capability (79 mAh g-1 at 50 A g-1 in ether-based electrolyte and 124 mAh g-1 at 10 A g-1 in carbonate-based electrolyte). In addition, the potential of BTT-PTO-COF electrode for prototype batteries has been demonstrated by full cells of dual-ion (FDIBs), which attain comparable electrochemical performances to the half cells. Moreover, mechanism studies combining ex situ characterization and theoratical calculations reveal the efficient dual-ion storage process and facile charge transfer of BTT-PTO-COF. This work not only expands the diversity of redox-active COFs but also provide concept of structure design for high-rate and high-capacity organic electrodes.

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.

Research Progress in Donor-Acceptor Type Covalent Organic Frameworks

Covalent organic frameworks (COFs) are new organic porous materials constructed by covalent bonds, with the advantages of pre-designable topology, adjustable pore size, and abundant active sites. Many research studies have shown that COFs exhibit great potential in gas adsorption, molecular separation, catalysis, drug delivery, energy storage, etc. However, the electrons and holes of intrinsic COF are prone to compounding in transport, and the carrier lifetime is short. The donor-acceptor (D-A) type COFs, which are synthesized by introducing D and A units into the COFs backbone, combine separated electron and hole migration pathway, tunable band gap and optoelectronic properties of D-A type polymers with the unique advantages of COFs and have made great progress in related research in recent years. Here, the synthetic strategies of D-A type COFs are first outlined, including the rational design of linkages and D-A units as well as functionalization approaches. Then the applications of D-A type COFs in catalytic reactions, photothermal therapy, and electronic materials are systematically summarized. In the final section, the current challenges, and new directions for the development of D-A type COFs are presented.

Unique Octupolar 2D-Polymer Frameworks as Mixed Conductors and Metal-Free Catalysts for Dual-Promoted Li and S Electrochemistry: Multi-regulation Role of Ethoxylation Chemistry

Here, we for the first time introduce ethoxylation chemistry to develop a new octupolar cyano-vinylene-linked 2D polymer framework (Cyano-OCF-EO) capable of acting as efficient mixed electron/ion conductors and metal-free sulfur evolution catalysts for dual-promoted Li and S electrochemistry. Our strategy creates a unique interconnected network of strongly-coupled donor 3-(acceptor-core) octupoles in Cyano-OCF-EO, affording enhanced intramolecular charge transfer, substantial active sites and crowded open channels. This enables Cyano-OCF-EO as a new versatile separator modifier, which endows the modified separator with superior catalytic activity for sulfur conversion and rapid Li ion conduction with the high Li+ transference number up to 0.94. Thus, the incorporation of Cyano-OCF-EO can concurrently regulate sulfur redox reactions and Li-ion flux in Li-S cells, attaining boosted bidirectional redox kinetics, inhibited polysulfide shuttle and dendrite-free Li anodes. The Cyano-OCF-EO-involved Li-S cell is endowed with excellent overall electrochemical performance especially large areal capacity of 7.5 mAh cm-2 at high sulfur loading of 8.7 mg cm-2 . Mechanistic studies unveil the dominant multi-promoting effect of the triethoxylation on electron and ion conduction, polysulfide adsorption and catalytic conversion as well as previously-unexplored -CN/C-O dual-site synergistic effect for enhanced polysulfide adsorption and reduced energy barrier toward Li2 S conversion.

One-Dimensional Covalent Organic Framework as High-Performance Cathode Materials for Lithium-Ion Batteries

Covalent organic frameworks (COFs) have emerged as a new class of cathode materials for energy storage in recent years. However, they are limited to two-dimensional (2D) or three-dimensional (3D) framework structures. Herein, this work reports designed synthesis of a redox-active one-dimensional (1D) COF and its composites with 1D carbon nanotubes (CNTs) via in situ growth. Used as cathode materials for Li-ion batteries, the 1D COF@CNT composites with unique dendritic core-shell structure can provide abundant and easily accessible redox-active sites, which contribute to improve diffusion rate of lithium ions and the corresponding specific capacity. This synergistic structural design enables excellent electrochemical performance of the cathodes, giving rise to 95% utilization of redox-active sites, high rate capability (81% capacity retention at 10 C), and long cycling stability (86% retention after 600 cycles at 5 C). As the first example to explore the application of 1D COFs in the field of energy storage, this study demonstrates the great potential of this novel type of linear crystalline porous polymers in battery technologies.

Porous Organic Polymer with Hierarchical Structure and Limited Volume Expansion for Ultrafast and Highly Durable Sodium Storage

Sustainable organic electrode materials, as promising alternatives to conventional inorganic electrode materials for sodium-ion batteries (SIBs), are still challenging to realize long-lifetime and high-rate batteries because of their poor conductivity, limited electroactivity, and severe dissolution. It is also urgent to deeply reveal their electrochemical mechanism and evolution processes. A porous organic polymer (POP) with a conjugated and hierarchical structure is designed and synthesized here. The unique molecule and structure endow the POP with electron delocalization, high ionic diffusivity, plentiful active sites, exceptional structure stability, and limited solubility in electrolytes. When evaluated as an anode for SIBs, the POP exhibits appealing electrochemical properties regarding reversible capacity, rate behaviors, and long-duration life. Importantly, using judiciously combined experiments and theoretical computation, including in situ transmission electron microscopy (TEM), and ex situ spectroscopy, we reveal the Na-storage mechanism and dynamic evolution processes of the POP, including 12-electron reaction process with Na, low volume expansion (125-106% vs the initial 100%), and stable composition and structure evolution during repeating sodiation/de-sodiation processes. This quantitative design for ultrafast and highly durable sodium storage in the POP could be of immediate benefit for the rational design of organic electrode materials with ideal electrochemical properties.

Covalent Organic Frameworks: Recent Progress in Biomedical Applications

Covalent organic frameworks (COFs) are a type of crystalline organic porous material with specific features and interesting structures, including porosity, large surface area, and biocompatibility. These features enable COFs to be considered as excellent candidates for applications in various fields. Recently, COFs have been widely demonstrated as promising materials for biomedical applications because of their excellent physicochemical properties and ultrathin structures. In this review, we cover the recent progress of COF materials for applications in photodynamic therapy, gene delivery, photothermal therapy, drug delivery, bioimaging, biosensing, and combined therapies. Moreover, the critical challenges and further perspectives with regards to COFs for future biology-facing applications are also discussed.

Triphenylamine-anthraquinone based donor-acceptor conjugated microporous polymers for photocatalytic hydroxylation of phenylboronic acids

Triphenylamine-based donor-acceptor conjugated microporous polymers, namely PTPA-AQ and PTPA-AM, were synthesized for the first time via Suzuki-Miyaura coupling of tris(4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)phenyl)-amine as a donor with 2,6-dibromoanthracene-9,10-dione and 2,2'-(2,6-dibromoanthracene-9,10-diylidene)dimalononitrile acceptors for efficient visible-light driven oxidative hydroxylation of various phenylboronic acids. The dimalononitrile derivative having greater acceptor ability showed tunable photophysical properties of PTPA-AM (lower band gap of 1.47 eV and better exciton separation efficiency) as well as porosity (lower Brunauer-Emmett-Teller (BET) surface area of 43 m² g^-1). PTPA-AQ having higher BET surface area (400 m² g^-1), suitable HOMO-LUMO positions and an optimal band gap (1.94 eV) showed better photocatalytic activity for the hydroxylation with yields up to 96%.

Sustainably Recycling and Upcycling of Single-Use Plastic Wastes through Heterogeneous Catalysis

The huge amount of plastic waste has caused a series of environmental and economic problems. Depolymerization of these wastes and their conversion into desired chemicals have been regarded as a promising route for dealing with these issues, which strongly relies on catalysis for C-C and C-O bond cleavage and selective transformation. Here, we reviewed recent developments in catalysis systems for dealing with single-use plastics, such as polyethylene, polypropylene, and polyethylene glycol terephthalate. The recycling processes of depolymerization into original monomers and conversion into other economic-incentive chemicals were systemically discussed. Rational designs of catalysts for efficient conversion were particularly highlighted. Overall, improving the tolerance of catalysts to impurities in practical plastics, reducing the economic cost during the catalytic depolymerization process, and trying to obtain gaseous hydrogen from plastic wastes are suggested as the developing trends in this field.

Construction of Macroporous Co2SnO4 with Hollow Skeletons as Anodes for Lithium-Ion Batteries

Increasing the energy density of lithium-ion batteries (LIBs) can broaden their applications in energy storage but remains a formidable challenge. Herein, with polyacrylic acid (PAA) as phase separation agent, macroporous Co₂SnO₄ with hollow skeletons was prepared by sol-gel method combined with phase separation. As the anode of LIBs, the macroporous Co₂SnO₄ demonstrates high capacity retention (115.5% at 200 mA·g⁻¹ after 300 cycles), affording an ultrahigh specific capacity (921.8 mA h·g⁻¹ at 1 A·g⁻¹). The present contribution provides insight into engineering porous tin-based materials for energy storage.

Quinone-based conjugated polymer cathodes synthesized via direct arylation for high performance Li-organic batteries

Direct arylation cross-coupling reaction was employed to prepare quinone-based conjugated polymer cathodes, which realize a high reversible capacity of 200 mA h g^-1 at 0.05 A g^-1, an excellent rate capability of 111 mA h g^-1 at 30 A g^-1 (150C), and a stable cycling performance for more than 3000 cycles.

Porous organic polymers for Li-chemistry-based batteries: functionalities and characterization studies

Porous organic polymers (POPs), a versatile class of materials that possess many tunable properties such as high chemical absorptivity and ionic conductivity, are emerging candidate electrode materials, permselective membranes, ionic conductors, interfacial stabilizers and functional precursors to synthesize advanced porous carbon. Based on their crystal structure features, the emerging POPs can be classified into two subclasses: amorphous POPs (hyper cross-linked polymers, polymers with intrinsic microporosity, conjugated microporous polymers, porous aromatic frameworks, etc.) and crystalline POPs (covalent organic frameworks, etc.). This tutorial review provides a brief introduction of different types of POPs in terms of their classification and functions for tackling the remaining challenges in various types of Li-chemistry-based batteries. In situ and ex situ characterization studies are also discussed to highlight their importance and applicability for the structural investigation of POPs to reveal the underlying mechanism of POPs over the course of the electrochemical process. Although some revolutionary advances have been achieved, the development of POPs in Li-chemistry-based batteries is still in its infancy. Perspectives regarding future application and mechanistic insights of POPs in battery studies are outlined at the end.

Capturing Visible Light in Low-Band-Gap C4 N-Derived Responsive Bifunctional Air Electrodes for Solar Energy Conversion and Storage

We report facile synthesis of low-band-gap mesoporous C₄ N particles and their use as responsive bifunctional oxygen catalysts for visible-light-sensitive (VLS) rechargeable Zn-air battery (RZAB) and polymer-air battery (RPAB). Compared to widely studied g-C₃ N₄ , C₄ N shows a smaller band gap of 1.99 eV, with a larger photocurrent response, and it can function as visible-light-harvesting antenna and bifunctional oxygen reduction/evolution (ORR/OER) catalysts, enabling effective photocoupling to tune oxygen catalysis. The C₄ N-enabled VLS-RZAB displays a low charge voltage of 1.35 V under visible light, which is below the theoretical RZAB voltage of 1.65 V, corresponding to a high energy efficiency of 97.78 %. Pairing a C₄ N cathode with a polymer anode also endows an VLS-RPAB with light-boosted charge performance. It is revealed that the ORR and OER active sites in C₄ N are separate carbon sites near pyrazine-nitrogen atoms and photogenerated energetic holes can activate OER for improved reaction kinetics.