Conductive 2D metal-organic framework for high-performance cathodes in aqueous rechargeable zinc batteries

Redox-Bipolar Covalent Organic Framework Cathode for Advanced Sodium-Organic Batteries

Redox-active covalent organic frameworks (COFs) are promising candidates for sodium-ion batteries (SIBs). However, the construction of redox-bipolar COFs with the anions and cations co-storage feature for SIBs is rarely reported. Herein, redox-bipolar COF constructed from aniline-fused quinonoid units (TPAD-COF) is developed as the cathode material in SIBs for the first time. The unique integration of conductive aniline skeletons and quinone redox centers endows TPAD-COF with high ionic/electrical conductivity, abundant redox-active sites, and fascinating bipolar features. Consequently, the elaborately tailored TPAD-COF cathode exhibits higher specific capacity (186.4 mAh g-1 at 0.05 A g-1) and superior cycling performance (over 2000 cycles at 1.0 A g-1 with 0.015% decay rate per cycle). Impressively, TPAD-COF also displays a high specific capacity of 101 mAh g-1 even at -20 °C. As a proof of concept, all-organic SIBs (AOSIBs) are assembled using TPAD-COF cathode and disodium terephthalate anode, which also show impressive electrochemical properties, indicating the potential application of TPAD-COF cathode in AOSIBs. The work will pave the avenue toward advanced COFs cathode for rechargeable batteries through rational molecular design.

Realizing the Electrode Engineering Significance Through Porous Organic Framework Materials for High-Capacity Aqueous Zn-Alkaline Battery

Energy storage technologies are eminently developed to address renewable energy utilization efficiently. Porous framework materials possess high surface area and pore volume, allowing for efficient ion transportation and storage. Their unique structure facilitates fast electron transfer, leading to improved battery kinetics. Porous organic framework materials like metal-organic (MOF) and covalent organic (COF) frameworks have immense potential in enhancing the charge/discharge performances of aqueous Zn-alkaline batteries. Organic frameworks and their derivatives can be modified feasibly to exhibit significant chemical stability, enabling them to tolerate the harsh battery environment. Zn-alkaline batteries can achieve enhanced energy density, longer lifespan, and improved rechargeability by incorporating MOFs and COFs, such as electrodes, separators, or electrolyte additives, into the battery architecture. The present review highlights the significant electrode design strategies based on porous framework materials for aqueous Zn-alkaline batteries, such as Zn-Ni, Zn-Mn, Zn-air, and Zn-N2/NO3 batteries. Besides, the discussion on the issues faced by the Zn anode and the essential anode design strategies to solve the issues are also included.

Molecular-Level Pore Tuning in 2D Conductive Metal-Organic Frameworks for Advanced Supercapacitor Performance

Two-dimensional (2D) electrically conductive metal-organic frameworks (MOFs) have emerged as viable candidates for active electrode materials in supercapacitors due to their high electrical conductivity, high specific surface area, and intrinsic redox-active sites. Despite their promising electrochemical performance, their pseudocapacitive behavior via fast and reversible charge transfer reactions remains yet to be fully exploited. Here, we investigate the electrochemical energy storage mechanism of Cu3(HHTATP)2 (HHTATP = 2,3,6,7,10,11-hexahydroxy-1,5,9-triaminotriphenylene), a 2D conductive MOF featuring characteristic redox-active pendant aromatic amines. Cu3(HHTATP)2 exhibited pseudocapacitive charge storage with an average gravimetric capacitance of 340 ± 15 F g-1 at a discharge rate of 0.2 A g-1 and maintained a capacitance retention over 90% after 7000 galvanostatic cycles at 5 A g-1. The polar pendant amines not only enhanced capacitance via additional amine/imine redox activity but also reduced interfacial charge transfer resistance through modified electrode-electrolyte interactions. These results highlight the potential of molecular-level pore environment tuning as a strategic approach in materials design for energy storage applications.

Hyaluronic acid modified Cu/Mn-doped metal-organic framework nanocatalyst for chemodynamic therapy

Chemodynamic therapy (CDT) is a new method for cancer treatment that produces highly toxic reactive oxygen species (ROS) in the tumor microenvironment to induce cancer cell apoptosis or necrosis. However, the therapeutic effect of CDT is often hindered by intracellular H2O2deficiency and the activity of antioxidants such as glutathione (GSH). In this study, a nano-catalyst HCM was developed using a self-assembled Cu/Mn-doped metal-organic framework, and its surface was modified with hyaluronic acid to construct a tumor-targeting CDT therapeutic agent with improved the efficiency and specificity. Three substances HHTP (2, 3, 6, 7, 10, 11-hexahydroxybenzophenanthrene), Cu2+, and Mn2+were shown to be decomposed and released under weakly acidic conditions in tumor cells. HHTP produces exogenous H2O2in the presence of oxygen to increase the H2O2content in tumors, Cu2+reduces GSH content and generates Cu+in the tumor, and Cu+and Mn2+catalyze H2O2to produce ∙OH in a Fenton-like reaction. Together, these three factors change the tumor microenvironment and improve the efficiency of ROS production. HCM showed selective and efficient cytotoxicity to cancer cells, and could effectively inhibit tumor growthin vivo, indicating a good CDT effect.

Sulfurized Two-Dimensional Conductive Metal-Organic Framework as a High-Performance Cathode Material for Rechargeable Mg Batteries

Rechargeable Mg batteries are a promising energy storage technology to overcome the limitations inherent to Li ion batteries. A critical challenge in advancing Mg batteries is the lack of suitable cathode materials. In this work, we report a cathode design that incorporates S functionality into two-dimensional metal-organic-frameworks (2D-MOFs). This new cathode material enables good Mg2+ storage capacity and outstanding cyclability. It was found that upon the initial Mg2+ insertion and disinsertion, there is an apparent structural transformation that crumbles the layered 2D framework, leading to amorphization. The resulting material serves as the active material to host Mg2+ through reduction and/or oxidation of S and, to a limited extent, O. The reversible nature of S and O redox chemistry was confirmed by spectroscopic characterizations and validated by density functional calculations. Importantly, during the Mg2+ insertion and disinsertion process, the 2D nature of the framework was maintained, which plays a key role in enabling the high reversibility of the MOF cathode.

Two-Dimensional (2D) Conductive Metal-Organic Framework Thin Films: The Preparation and Applications in Electrochemistry

Two-dimensional conductive MOF thin films have attracted attention due to their rich pore structure and unique electrical properties, and their applications in many fields, including batteries, sensing, supercapacitors, electrocatalysis, etc. This paper discusses several preparation methods for 2D conductive MOF thin films. And the applications of 2D conductive MOF thin films are summarized. In addition, the current challenges in the preparation of 2D conductive MOF thin films and the great potential in practical applications are discussed.

Toward Practical Multivalent Ion Batteries with Quinone-Based Organic Cathodes

Multivalent ion batteries have emerged as promising solutions to meet the future demands of energy storage applications, offering not only high energy density but also diverse socio-economic advantages. Among the various options for cathodes, quinone-based organic compounds have gained attention as suitable active materials for multivalent ion batteries due to their well-aligned ion channels, flexible structures, and competitive electrochemical performance. However, the charge carriers associated with anions that are often exploited in multivalent ion battery systems operate by way of a "non-rocking-chair" mechanism, which requires the use of an excess amount of electrolyte and results in a significant decrease in the energy density. In this review, by categorizing the various charge carriers exploited in previous studies on multivalent ion batteries, we summarize recently reported quinone-based organic cathodes for multivalent ion batteries and emphasize the importance of accurately identifying the charge carriers for calculating the energy density. We also propose potential future directions toward the practical realization of multivalent ion batteries, in link with their efficient energy storage applications.

Regulation of Electron Delocalization Region in 2D Heteroligand-Based Copper-Organic Framework to Enhance NH 4 + $ \rm {NH_{4}}{^+}$ Charge Storage

The rechargeable aqueous ammonium ion battery shows great potential in low-cost energy storage system because of its long life and environmental friendliness. However, most inorganic host materials used in ammonium ion batteries are still limited by slow diffusion kinetics. Herein, it is identified that a 2D heteroligand-based copper-organic framework featuring numerous ammonium ion adsorption site in the π-conjugated periodic skeleton supplies multiple accessible redox-active sites for high-performance ammonium storage. Benefitting from the effective regulation of electron delocalization by heteroligand and the inherent hydrogen bond cage mechanism between ammonium ions, the resultant full battery delivers a large specific energy density of 211.84 Wh kg-1, and it can be stably operated for 12000 cycles at 5 A g-1 for over 80 days. This explanatory understanding provides a new idea for the rational design of high-performance MOF-based ammonium ion battery cathode materials for efficient energy storage and conversion in the future.

Single-Atom Catalysts in Conductive Metal-Organic Frameworks: Enabling Reversible Gas Sensing at Room Temperature

Conductive metal-organic frameworks (cMOFs) offer high porosity and electrical conductivity simultaneously, making them ideal for application in chemiresistive sensors. Recently, incorporating foreign elements such as catalytic nanoparticles into cMOFs has become a typical strategy to enhance their sensing properties. However, this approach has led to critical challenges, such as pore blockage that impedes gas diffusion, as well as limited improvement in reversibility. Herein, single-atom catalyst (SAC)-functionalized cMOF is presented as a robust solution to the current limitations. Facile functionalization of SACs in a cMOF can be achieved through electrochemical deposition of metal precursors. As a proof of concept, a Pd SAC-functionalized cMOF is synthesized. The Pd SACs are stabilized at the interplanar sites of cMOF with Pd-N4 coordination while preserving the porosity of the MOF matrix. Notably, the microenvironment created by Pd SACs prevents irreversible structural distortion of cMOFs and facilitates a reversible charge transfer with NO2. Consequently, the cMOF exhibits a fully recoverable NO2 response, which was not previously attainable with the nanoparticle functionalization. Additionally, with the combination of preserved porosity for gas diffusion, it demonstrates the fastest level of response and recovery speed compared to other 2D-cMOFs of this class.

Recent Progress of Low-Dimensional Metal-Organic Frameworks for Aqueous Zinc-Based Batteries

Aqueous zinc-based batteries (AZBs) are promising energy storage solutions with remarkable safety, abundant Zn reserve, cost-effectiveness, and relatively high energy density. However, AZBs still face challenges such as anode dendrite formation that reduces cycling stability and limited cathode capacity. Recently, low-dimensional metal-organic frameworks (LD MOFs) and their derivatives have emerged as promising candidates for improving the electrochemical performance of AZBs owing to their unique morphologies, high structure tunability, high surface areas, and high porosity. However, clear guidelines for developing LD MOF-based materials for high-performance AZBs are scarce. In this review, the recent progress of LD MOF-based materials for AZBs is critically examined. The typical synthesis methods and structural design strategies for improving the electrochemical performance of LD MOF-based materials for AZBs are first introduced. The recent noteworthy research achievements are systematically discussed and categorized based on their applications in different AZB components, including cathodes, anodes, separators, and electrolytes. Finally, the limitations are addressed and the future perspectives are outlined for LD MOFs and their derivatives in AZB applications. This review provides clear guidance for designing high-performance LD MOF-based materials for advanced AZBs.

Redox Synergy: Enhancing Gas Sensing Stability in 2D Conjugated Metal-Organic Frameworks via Balancing Metal Node and Ligand Reactivity

Two-dimensional conjugated metal-organic frameworks (2D c-MOFs) have emerged as promising candidates in gas sensing, owing to their tunable porous structure and conductivity. Nevertheless, the reported gas sensing mechanisms heavily relied on electron transfer between metal nodes and gas molecules. Normally, the strong interaction between the metal sites and target gas molecule would result poor recovery and thus bad recycling property. Herein, we propose a redox synergy strategy to overcome this issue by balancing the reactivity of metal sites and ligands. A 2D c-MOF, Zn3(HHTQ)2, was prepared for nitrogen dioxide (NO2) sensing, which was constructed from active ligands (hexahydroxyltricycloquinazoline, HHTQ) and inactive transition-metal ions (Zn2+). Substantial characterizations and theoretical calculations demonstrated that by utilizing only the redox interactions between ligands and NO2, not only high sensitivity and selectivity, but also excellent cycling stability in NO2 sensing could be achieved. In contrast, control experiments employing isostructural 2D c-MOFs with Cu/Ni metal nodes exhibited irreversible NO2 sensing. Our current work provides a new design strategy for gas sensing materials, emphasizing harnessing the redox activity of only ligands to enhance the stability of MOF sensing materials.

Chelated Metal-Organic Frameworks for Improved the Performance of High-Nickel Cathodes in Lithium-Ion Batteries

Lithium-ion batteries have gained widespread use in various applications, including portable devices, electric vehicles, and energy storage systems. High Ni cathode, LiNixCoyMnzO2 (NCM, x≥0.8, x+y+z=1), have garnered significant attention owing to their high energy density. However, the limited Li-ion transfer rate and transition metal cross-talk to anode pose obstacles to further improvement of electrochemical performance. To tackle these challenges, metal-organic frameworks (MOFs) with chelating agents are employed as additive materials for electrode. MOFs with chelating agents offer three key attributes: (1) Effective mitigation of transition metal cross-talk to the anode, (2) Partial desolvation of Li+ ions through MOF pores, and (3) Immobilization of anions via metal sites in the MOF. Leveraging these advantages, the chelating MOF-modified NCM cathode demonstrates reduced charge transfer resistance, both in their pristine and cycled states. In addition, they exhibit significantly improved the Li-ion diffusion coefficients after 100 cycles. These findings underscore the potential of MOFs with chelating agents as promising additive materials for enhancing the performance of LIBs.

2D Conductive Metal-Organic Frameworks Based on Tetraoxa[8]circulenes as Promising Cathode for Aqueous Zinc Ion Batteries

Aqueous zinc-ion batteries (ZIBs) are the new generation electrochemical energy storage systems. Recently, two-dimensional conductive metal-organic frameworks (2D c-MOFs) are attractive to serve as cathode materials of ZIBs due to their compositional diversity, abundant active sites, and excellent conductivity. Despite the growing interest in 2D c-MOFs, their application prospects are still to be explored. Herein, a tetraoxa[8]circulene (TOC) derivative with unique electronic structure and interesting redox-active property are synthesized to construct c-MOFs. A series of novel 2D c-MOFs (Cu-TOC, Zn-TOC and Mn-TOC) with different conductivities and packing modes are obtained by combining the linker tetraoxa[8]circulenes-2,3,5,6,8,9,11,12-octaol (8OH-TOC) and corresponding metal ions. Three c-MOFs all exhibit typical semiconducting properties, and Cu-TOC exhibits the highest electrical conductivity of 0.2 S cm-1 among them. Furthermore, their electrochemical performance as cathode materials for ZIBs have been investigated. They all performed high reversible capacity, decent cycle stability and excellent rate capability. This work reveals the key insights into the electrochemical application potential of 2D c-MOFs and advances their development as cathode materials in ZIBs.

Phytic Acid Customized Hydrogel Polymer Electrolyte and Prussian Blue Analogue Cathode Material for Rechargeable Zinc Metal Hydrogel Batteries

Zinc anode deterioration in aqueous electrolytes, and Zn dendrite growth is a major concern in the operation of aqueous rechargeable Zn metal batteries (AZMBs). To tackle this, the replacement of aqueous electrolytes with a zinc hydrogel polymer electrolyte (ZHPE) is presented in this study. This method involves structural modifications of the ZHPE by phytic acid through an ultraviolet (UV) light-induced photopolymerization process. The high membrane flexibility, high ionic conductivity (0.085 S cm-1), improved zinc corrosion overpotential, and enhanced electrochemical stability value of ≈2.3 V versus Zn|Zn2+ show the great potential of ZHPE as an ideal gel electrolyte for rechargeable zinc metal hydrogel batteries (ZMHBs). This is the first time that the dominating effect of chelation of phytic acid with M2+ center over H-bonding with water is described to tune the gel electrolyte properties for battery applications. The ZHPE shows ultra-high stability over 360 h with a capacity of 0.50 mAh cm-2 with dendrite-free plating/stripping in Zn||Zn symmetric cell. The fabrication of the ZMHB with a high-voltage zinc hexacyanoferrate (ZHF) cathode shows a high-average voltage of ≈1.6 V and a comparable capacity output of 63 mAh g-1 at 0.10 A g-1 of the current rate validating the potential application of ZHPE.

In situ fast self-assembled preparation of dandelion-like Cu(OH)2@Cu3(HHTP)2 with core-shell heterostructure arrays for electrochemical sensing of formaldehyde in food samples

Formaldehyde is known to harm the respiratory, nervous, and digestive systems of people. In this paper, a novel dandelion-like electrocatalyst with core-shell heterostructure arrays were fast self-assembled prepared in situ using copper foam (CF) as support substrate and 2,3,6,7,10,11 hexahydroxy-triphenyl (HHTP) as ligand (Cu(OH)2@Cu3(HHTP)2/CF) by a simple two-step hydrothermal reaction. The 1D Cu(OH)2 nanorods "core" and the 2D π-conjugated conducting metal-organic frameworks (Cu3(HHTP)2cMOF) "shell" with remote delocalized electrons give the dandelion-like heterogeneous catalysts excellent electrochemical activity such as a large specific surface area, high conductivity and a fast electron transfer rate. The Cu(OH)2@Cu3(HHTP)2/CF exhibited excellent electrocatalytic performance for formaldehyde under alkaline conditions with a linear range of 0.2 μmol/L - 125 μmol/L and 125 μmol/L - 8 mmol/L, a detection limit as low as 15.9 nmol/L (S/N = 3), as well as good accuracy, consistency, and durability, and it effectively identified FA in food.

Synthesis of a highly conductive coordination polymer film via a vapor-solid phase chemical conversion process

A novel vapor-solid phase chemical conversion process is reported here to synthesise high-quality films of the conductive coordination polymer (c-CP) Ag5BHT (BHT = benzenehexanothiolate), which has the potential to be applied for the synthesis and processing of c-CP electronic devices. This approach involves reacting a silver oxide precursor and an H6BHT linker in an isopropanol solvent vapor atmosphere to obtain Ag5BHT thin films with controllable thickness (100-300 nm). The as-synthesized Ag5BHT thin films exhibit conductivities as high as 10 S cm-1. Additionally, under field-effect modulation, these nanofilms demonstrate remarkably high charge mobility (38 cm2 v-1 s-1).

Metal-organic frameworks for high-performance cathodes in batteries

Metal-organic frameworks (MOFs) are functional materials that are proving to be indispensable for the development of next-generation batteries. The porosity, crystallinity, and abundance of active sites in MOFs, which can be tuned by selecting the appropriate transition metal/organic linker combination, enable MOFs to meet the performance requirements for cathode materials in batteries. Recent studies on the use of MOFs in cathodes have verified their high durability, cyclability, and capacity thus demonstrating the huge potential of MOFs as high-performance cathode materials. However, to keep pace with the rapid growth of the battery industry, several challenges hindering the development of MOF-based cathode materials need to be overcome. This review analyzes current applications of MOFs to commercially available lithium-ion batteries as well as advanced batteries still in the research stage. This review provides a comprehensive outlook on the progress and potential of MOF cathodes in meeting the performance requirements of the future battery industry.

Arresting dissolution of two-dimensional metal-organic frameworks enables long life in electrochemical devices

Two-dimensional conjugated metal-organic frameworks (2D cMOFs) are emerging as promising materials for electrochemical energy storage (EES). Despite considerable interest, an understanding of their electrochemical stability and the factors contributing to their degradation during cycling is largely lacking. Here we investigate three Cu-based MOFs and report that the dissolution of 2D cMOFs into electrolytes is a prevalent and significant degradation pathway. Several factors, such as the inherent solubility of ligands in electrolyte solvents and the duration of charge-discharge cycling exert a strong influence on the dissolution process. When these factors combine within a MOF, severely limited cycling stability is observed, with dissolution accounting for up to 80% of capacity degradation. Conversely, excellent cycling stability is observed when testing a Cu-MOF with a sparingly soluble ligand within an optimized potential window. Overall, these findings represent essential insights into the electrochemical stability of 2D cMOFs, offering crucial guidelines for their targeted development in EES applications.

Self-Charging Aqueous Zn//COF Battery with UltraHigh Self-Charging Efficiency and Rate

Self-charging zinc batteries that combine energy harvesting technology with batteries are candidates for reliable self-charging power systems. However, the lack of rational materials design results in unsatisfactory self-charging performance. Here, a covalent organic framework containing pyrene-4,5,9,10-tetraone groups (COF-PTO) is reported as a cathode material for aqueous self-charging zinc batteries. The ordered channel structure of the COF-PTO provides excellent capacity retention of 98% after 18 000 cycles at 10 A g-1 and ultra-fast ion transfer. To visually assess the self-charging performance, two parameters, namely self-charging efficiency (self-charging discharge capacity/galvanostatic discharge capacity, η) and average self-charging rate (total discharge capacity after cyclic self-charging/total cyclic self-charging time, ν), are proposed for performance evaluation. COF-PTO achieves an impressive η of 96.9% and an ν of 30 mAh g-1 self-charge capacity per hour in 100 self-charging cycles, surpassing the previous reports. Mechanism studies reveal the co-insertion of Zn2+ and H+ double ions in COF-PTO of self-charging zinc batteries. In addition, the C═N and C═O (on the benzene) in COF-PTO are ortho structures to each other, which can easily form metal heterocycles with Zn ions, thereby driving the forward progress of the self-charging reaction and enhancing the self-charging performance.

Robust Chemiresistive Behavior in Conductive Polymer/MOF Composites

Metal-organic frameworks (MOFs) are promising materials for gas sensing but are often limited to single-use detection. A hybridization strategy is demonstrated synergistically deploying conductive MOFs (cMOFs) and conductive polymers (cPs) as two complementary mixed ionic-electronic conductors in high-performing stand-alone chemiresistors. This work presents significant improvement in i) sensor recovery kinetics, ii) cycling stability, and iii) dynamic range at room temperature. The effect of hybridization across well-studied cMOFs is demonstrated based on 2,3,6,7,10,11-hexahydroxytriphenylene (HHTP) and 2,3,6,7,10,11-hexaiminotriphenylene (HITP) ligands with varied metal nodes (Co, Cu, Ni). A comprehensive mechanistic study is conducted to relate energy band alignments at the heterojunctions between the MOFs and the polymer with sensing thermodynamics and binding kinetics. The findings reveal that hole enrichment of the cMOF component upon hybridization leads to selective enhancement in desorption kinetics, enabling significantly improved sensor recovery at room temperature, and thus long-term response retention. This mechanism is further supported by density functional theory calculations on sorbate-analyte interactions. It is also found that alloying cPs and cMOFs enables facile thin film co-processing and device integration, potentially unlocking the use of these hybrid conductors in diverse electronic applications.

Anion-Cation Competition Chemistry for Comprehensive High-Performance Prussian Blue Analogs Cathodes

The extensively studied Prussian blue analogs (PBAs) in various batteries are limited by their low discharge capacity, or subpar rate etc., which are solely reliant on the cation (de)intercalation mechanism. In contrast to the currently predominant focus on cations, we report the overlooked anion-cation competition chemistry (Cl-, K+, Zn2+) stimulated by high-voltage scanning. With our designed anion-cation combinations, the KFeMnHCF cathode battery delivers comprehensively superior discharge performance, including voltage plateau >2.0 V (vs. Zn/Zn2+), capacity >150 mAh g-1, rate capability with capacity maintenance above 96 % from 0.6 to 5 A g-1, and cyclic stability exceeding 3000 cycles. We further verify that such comprehensive improvement of electrochemical performance utilizing anion-cation competition chemistry is universal for different types of PBAs. Our work would pave a new and efficient road towards the next-generation high-performance PBAs cathode batteries.

Catalysis with Two-Dimensional Metal-Organic Frameworks: Synthesis, Characterization, and Modulation

The demand for the exploration of highly active and durable electro/photocatalysts for renewable energy conversion has experienced a significant surge in recent years. Metal-organic frameworks (MOFs), by virtue of their high porosity, large surface area, and modifiable metal centers and ligands, have gained tremendous attention and demonstrated promising prospects in electro/photocatalytic energy conversion. However, the small pore sizes and limited active sites of 3D bulk MOFs hinder their wide applications. Developing 2D MOFs with tailored thickness and large aspect ratio has emerged as an effective approach to meet these challenges, offering a high density of exposed active sites, better mechanical stability, better assembly flexibility, and shorter charge and photoexcited state transfer distances compared to 3D bulk MOFs. In this review, synthesis methods for the most up-to-date 2D MOFs are first overviewed, highlighting their respective advantages and disadvantages. Subsequently, a systematic analysis is conducted on the identification and electronic structure modulation of catalytic active sites in 2D MOFs and their applications in renewable energy conversion, including electrocatalysis and photocatalysis (electro/photocatalysis). Lastly, the current challenges and future development of 2D MOFs toward highly efficient and practical electro/photocatalysis are proposed.

Tackling the Challenges of Aqueous Zn-Ion Batteries via Polymer-Derived Strategies

Zn-ion batteries (ZIBs) have gathered unprecedented interest recently benefiting from their intrinsic safety, affordability, and environmental benignity. Nevertheless, their practical implementation is hampered by low rate performance, inferior Zn2+ diffusion kinetics, and undesired parasitic reactions. Innovative solutions are put forth to address these issues by optimizing the electrodes, separators, electrolytes, and interfaces. Remarkably, polymers with inherent properties of low-density, high processability, structural flexibility, and superior stability show great promising in tackling the challenges. Herein, the recent progress in the synthesis and customization of functional polymers in aqueous ZIBs is outlined. The recent implementations of polymers into each component are summarized, with a focus on the inherent mechanisms underlying their unique functions. The challenges of incorporating polymers into practical ZIBs are also discussed and possible solutions to circumvent them are proposed. It is hoped that such a deep analysis could accelerate the design of polymer-derived approaches to boost the performance of ZIBs and other aqueous battery systems as they share similarities in many aspects.

Electrolyte and Additive Engineering for Zn Anode Interfacial Regulation in Aqueous Zinc Batteries

Aqueous Zn-metal batteries (AZMBs) have gained great interest due to their low cost, eco-friendliness, and inherent safety, which serve as a promising complement to the existing metal-based batteries, e.g., lithium-metal batteries and sodium-metal batteries. Although the utilization of aqueous electrolytes and Zn metal anode in AZMBs ensures their improved safety over other metal batteries meanwhile guaranteeing their decent energy density at the cell level, plenty of challenges involved with metallic Zn anode still await to be addressed, including dendrite growth, hydrogen evolution reaction, and zinc corrosion and passivation. In the past years, several attempts have been adopted to address these problems, among which engineering the aqueous electrolytes and additives is regarded as a facile and promising approach. In this review, a comprehensive summary of aqueous electrolytes and electrolyte additives will be given based on the recent literature, aiming at providing a fundamental understanding of the challenges associated with the metallic Zn anode in aqueous electrolytes, meanwhile offering a guideline for the electrolytes and additives engineering strategies toward stable AZMBs in the future.

Unveiling Organic Electrode Materials in Aqueous Zinc-Ion Batteries: From Structural Design to Electrochemical Performance

Aqueous zinc-ion batteries (AZIBs) are one of the most compelling alternatives of lithium-ion batteries due to their inherent safety and economics viability. In response to the growing demand for green and sustainable energy storage solutions, organic electrodes with the scalability from inexpensive starting materials and potential for biodegradation after use have become a prominent choice for AZIBs. Despite gratifying progresses of organic molecules with electrochemical performance in AZIBs, the research is still in infancy and hampered by certain issues due to the underlying complex electrochemistry. Strategies for designing organic electrode materials for AZIBs with high specific capacity and long cycling life are discussed in detail in this review. Specifically, we put emphasis on the unique electrochemistry of different redox-active structures to provide in-depth understanding of their working mechanisms. In addition, we highlight the importance of molecular size/dimension regarding their profound impact on electrochemical performances. Finally, challenges and perspectives are discussed from the developing point of view for future AZIBs. We hope to provide a valuable evaluation on organic electrode materials for AZIBs in our context and give inspiration for the rational design of high-performance AZIBs.

Understanding Electrolyte Ion Size Effects on the Performance of Conducting Metal-Organic Framework Supercapacitors

Layered metal-organic frameworks (MOFs) have emerged as promising materials for next-generation supercapacitors. Understanding how and why electrolyte ion size impacts electrochemical performance is crucial for developing improved MOF-based devices. To address this, we investigate the energy storage performance of Cu3(HHTP)2 (HHTP = 2,3,6,7,10,11-hexahydroxytriphenylene) with a series of 1 M tetraalkylammonium tetrafluoroborate (TAABF4) electrolytes with different cation sizes. Three-electrode experiments show that Cu3(HHTP)2 exhibits an asymmetric charging response with all ion sizes, with higher energy storage upon positive charging and a greater charging asymmetry with larger TAA+ cations. The results further show that smaller TAA+ cations demonstrate superior capacitive performances upon both positive and negative charging compared to larger TAA+ cations. To gain further insights, electrochemical quartz crystal microbalance measurements were performed to probe ion electrosorption during charging and discharging. These reveal that Cu3(HHTP)2 has a cation-dominated charging mechanism, but interestingly indicate that the solvent also participates in the charging process with larger cations. Overall, the results of this study suggest that larger TAA+ cations saturate the pores of the Cu3(HHTP)2-based electrodes. This leads to more asymmetric charging behavior and forces solvent molecules to play a role in the charge storage mechanism. These findings significantly enhance our understanding of ion electrosorption in layered MOFs, and they will guide the design of improved MOF-based supercapacitors.

Development of Inverse-Opal-Structured Charge-Deficient Co9S8@nitrogen-Doped-Carbon to Catalytically Enable High Energy and High Power for the Two-Electron Transfer I+/I- Electrode

The iodine (I) electrode involving two-electron transfer chemistry by converting between I+ and I-, has the potential to deliver theoretically doubled capacity and higher working voltage platforms, thus achieving higher energy density. However, owing to the slow kinetics of the cascade two-electron transfer reactions, the system suffers from large overpotentials and low power density, especially at high working currents and low temperatures. Here, an inverse-opal-structured cobalt sulfide@nitrogen-doped-carbon (Co9S8@NC) catalyst with unique charge-deficient states is developed to promote the reaction kinetics of the I-/I+ electrode. The charge-deficient Co9S8@NC catalyst not only enables strong physicochemical adsorption with the iodine species but also significantly reduces the activation energy and interfacial charge transfer resistance of the cascade I+/I0/I- conversion reaction. Consequently, the prototypical Zn‖I+/I0/I- battery equipped with the Co9S8@NC catalyst can deliver a high energy density of 554 Wh kg-1 and a stable cycle life of 5000 cycles at 30 °C. Moreover, at a subzero temperature of -30 °C, the battery can exhibit enhanced kinetics and a high power density of 1514 W kg-1, high energy density of 485 Wh kg-1.

Aliovalent Substitution Tunes Physical Properties in a Conductive Bis(dithiolene) Two-Dimensional Metal-Organic Framework

Two-dimensional conductive metal-organic frameworks have emerged as promising electronic materials for applications in (opto)electronic, thermoelectric, magnetic, electrocatalytic, and energy storage devices. Many bottom-up or postsynthetic protocols have been developed to isolate these materials or further modulate their electronic properties. However, some methodologies commonly used in classic semiconductors, notably, aliovalent substitution, are conspicuously absent. Here, we demonstrate how aliovalent Fe(III) to Ni(II) substitution enables the isolation of a Ni bis(dithiolene) material from a previously reported Fe analogue. Detailed characterization supports the idea that aliovalent substitution of Fe(III) to Ni(II) results in an in situ oxidation of the organic dithiolene linker. This substitution-induced redox tuning modulates the electronic properties in the system, leading to higher electrical conductivity and Hall mobility but slightly lower carrier densities and weaker antiferromagnetic interactions. Moreover, this aliovalent substitution improves the material's electrochemical stability and thus enables pseudocapacitive behavior in the Ni material. These results demonstrate how classic aliovalent substitution strategies in semiconductors can also be leveraged in conductive MOFs and add further support to this class of compounds as emerging electronic materials.

High-Performance Ni3(HHTP)2 Film-Based Flexible Field-Effect Transistor Gas Sensors

Conductive metal-organic frameworks (MOFs) have received increasing attention in recent years and present high application potential as sensing elements in electronic sensors. In this study, flexible field-effect transistor (FET) sensors based on conductive MOF, i.e., Ni3(HHTP)2, have been constructed. This Ni3(HHTP)2 sensor has high sensitivity (detection limit of 56 ppb) as well as superior selectivity for NO2 detection at room temperature, which is demonstrated by accurate gas detection in a mixed gas atmosphere. Moreover, by employing six flexible substrates, i.e., polyimide (PI), tape (PET), facemask, paper cup, tablecloth, and take-out bag (textile), we successfully demonstrate the universality of the flexible sensor construction with conductive MOF as sensing film on various substrates. This study of conductive MOF-based flexible electronic sensors offers a new opportunity for a wide range of sensing applications with wearable and portable electronic devices.

Regulation of the d-band center of metal-organic frameworks for energy-saving hydrogen generation coupled with selective glycerol oxidation

The hybrid electrolyzer coupled glycerol oxidation (GOR) with hydrogen evolution reaction (HER) is fascinating to simultaneously generate H2 and high value-added chemicals with low energy input, yet facing a challenge. Herein, Cu-based metal-organic frameworks (Cu-MOFs) are reported as model catalysts for both HER and GOR through doping of atomically dispersed precious and nonprecious metals. Remarkably, the HER activity of Ru-doped Cu-MOF outperformed a Pt/C catalyst, with its Faradaic efficiency for formate formation at 90% at a low potential of 1.40 V. Furthermore, the hybrid electrolyzer only needed 1.36 V to achieve 10 mA cm-2, 340 mV lower than that for splitting pure water. Theoretical calculations demonstrated that electronic interactions between the host and guest (doped) metals shifted downward the d-band centers (εd) of MOFs. This consequently lowered water adsorption and dissociation energy barriers and optimized hydrogen adsorption energy, leading to significantly enhanced HER activities. Meanwhile, the downshift of εd centers reduced energy barriers for rate-limiting step and the formation energy of OH*, synergistically enhancing the activity of MOFs for GOR. These findings offered an effective means for simultaneous productions of hydrogen fuel and high value-added chemicals using one hybrid electrolyzer with low energy input.

Unlocking Double Redox Reaction of Metal-Organic Framework for Aqueous Zinc-Ion Battery

Metal-organic frameworks (MOFs) show wide application as the cathode of aqueous zinc-ion batteries (AZIBs) in the future owning to their high porosity, diverse structures, abundant species, and controllable morphology. However, the low energy density and poor cycling stability hinder the feasibility in practical application. Herein, an innovative strategy of organic/inorganic double electroactive sites is proposed and demonstrated to obtain extra capacity and enhance the energy density in a manganese-based metal-organic framework (Mn-MOF-74). Simultaneously, its energy storage mechanism is systematically investigated. Moreover, profiting from the coordination effect, the Mn-MOF-74 features with stable structure in ZnSO4 electrolyte. Therefore, the Zn/Mn-MOF-74 batteries exhibit a high energy density and superior cycling stability. This work aids in the future development of MOFs in AZIBs.

Topologically Tunable Conjugated Metal-Organic Frameworks for Modulating Conductivity and Chemiresistive Properties for NH3 Sensing

Electrically conductive metal-organic frameworks (cMOFs) have garnered significant attention in materials science due to their potential applications in modern electrical devices. However, achieving effective modulation of their conductivity has proven to be a major challenge. In this study, we have successfully prepared cMOFs with high conductivity by incorporating electron-donating fused thiophen rings in the frameworks and extending their π-conjugated systems through ring-closing reactions. The conductivity of cMOFs can be precisely modulated ranging from 10-3 to 102 S m-1 by regulating their dimensions and topologies. Furthermore, leveraging the inherent tunable electrical properties based on topology, we successfully demonstrated the potential of these materials as chemiresistive gas sensors with an outstanding response toward 100 ppm NH3 at room temperature. This work not only provides valuable insights into the design of functional cMOFs with different topologies but also enriches the cMOF family with exceptional conductivity properties.

Acid-Dependent Charge Transport in a Solution-Processed 2D Conductive Metal-Organic Framework

The development of conductive metal-organic frameworks (MOFs) presents a unique challenge in materials chemistry because it is unclear how to dope them. Here, we demonstrate that the inclusion of pendant amines on hexahydroxytriphenylene linkages results in two-dimensional (2D) polycrystalline frameworks Cu3(HHTATP)2, isostructural to its Cu3(HHTP)2 parent, and exhibits the highest electrical conductivity of 1.21 S/cm among 2D MOFs featuring CuO4 metal nodes. Moreover, the bulk material can be treated with acid, resulting in a protonation-dependent increase in the conductivity. By spin-coating the acidic solution, we fabricated large-area thin films and collectively demonstrated an intuitive route to solution-processable, dopable, conductive MOFs.

Electrochemical Doping and Structural Modulation of Conductive Metal-Organic Frameworks

In this study, we introduce an electrochemical doping strategy aimed at manipulating the structure and composition of electrically conductive metal-organic frameworks (c-MOFs). Our methodology is exemplified through a representative c-MOF, Ni3(HITP)2 (HITP=2, 3, 6, 7, 10, 11-hexaiminotriphenylene), synthesized into porous thin films supported by nanocellulose. While the c-MOF exhibits characteristic capacitive behavior in neutral electrolyte; it manifests redox behaviors in both acidic and alkaline electrolytes. Evidence indicates that the organic ligands within c-MOF undergo oxidation (p-doping) and reduction (n-doping) when exposed to specific electrochemical potentials in acidic and alkaline electrolyte, respectively. Interestingly, the p-doping process proves reversible, with the c-MOF structure remaining stable across cyclic p-doping/de-doping. In contrast, the n-doping is irreversible, leading to the gradual decomposition of the framework into inorganic species over a few cycles. Drawing on these findings, we showcase the versatile electrochemical applications of c-MOFs and their derived composites, encompassing electrochemical energy storage, electrocatalysis, and ultrafast actuation. This study provides profound insights into the doping of c-MOFs, offering a new avenue for modulating their chemical and electronic structure, thereby broadening their potential for diverse electrochemical applications.

Large-Area Conductive MOF Ultrathin Film Controllably Integrating Dinuclear-Metal Sites and Photosensitizers to Boost Photocatalytic CO2 Reduction with H2O as an Electron Donor

Owing to the electrical conductivity and periodic porosity, conductive metal-organic framework (cMOF) ultrathin films open new perspectives to photocatalysis. The space-selective assembly of catalytic sites and photosensitizers in/on cMOF is favorable for promoting the separation of photogenerated carriers and mass transfer. However, the controllable integration of functional units into the cMOF film is rarely reported. Herein, via the synergistic effect of steric hindrance and an electrostatic-driven strategy, the dinuclear-metal molecular catalysts (DMC) and perovskite (PVK) quantum dot photosensitizers were immobilized into channels and onto the surface of cMOF ultrathin films, respectively, affording [DMC@cMOF]-PVK film photocatalysts. In this unique heterostructure, cMOF not only facilitated the charge transfer from PVK to DMC but also guaranteed mass transfer. Using H2O as an electron donor, [DMC@cMOF]-PVK realized a 133.36 μmol·g-1·h-1 CO yield in photocatalytic CO2 reduction, much higher than PVK and DMC-PVK. Owing to the excellent light transmission of films, multilayers of [DMC@cMOF]-PVK were integrated to increase the CO yield per unit area, and the 10-layer device realized a 1115.92 μmol·m-2 CO yield in 4 h, which was 8-fold higher than that of powder counterpart. This work not only lightens the development of cMOF-based composite films but also paves a novel avenue for an ultrathin film photocatalyst.

Single Zn Atoms with Acetate-Anion-Enabled Asymmetric Coordination for Efficient H2 O2 Photosynthesis

Exploring unique single-atom sites capable of efficiently reducing O2 to H2 O2 while being inert to H2 O2 decomposition under light conditions is significant for H2 O2 photosynthesis, but it remains challenging. Herein, we report the facile design and fabrication of polymeric carbon nitride (CN) decorated with single-Zn sites that have tailorable local coordination environments, which is enabled by utilizing different Zn salt anions. Specifically, the O atom from acetate (OAc) anion participates in the coordination of single-Zn sites on CN, forming asymmetric Zn-N3 O moiety on CN (denoted as CN/Zn-OAc), in contrast to the obtained Zn-N4 sites when sulfate (SO4 ) is adopted (CN/Zn-SO4 ). Both experimental and theoretical investigations demonstrate that the Zn-N3 O moiety exhibits higher intrinsic activity for O2 reduction to H2 O2 than the Zn-N4 moiety. This is attributed to the asymmetric N/O coordination, which promotes the adsorption of O2 and the formation of the key intermediate *OOH on Zn sites due to their modulated electronic structure. Moreover, it is inactive for H2 O2 decomposition under both dark and light conditions. As a result, the optimized CN/Zn-OAc catalyst exhibits significantly improved photocatalytic H2 O2 production activity under visible light irradiation.

Laser-Induced and MOF-Derived Metal Oxide/Carbon Composite for Synergistically Improved Ethanol Sensing at Room temperature

Advancements in sensor technology have significantly enhanced atmospheric monitoring. Notably, metal oxide and carbon (MOx/C) hybrids have gained attention for their exceptional sensitivity and room-temperature sensing performance. However, previous methods of synthesizing MOx/C composites suffer from problems, including inhomogeneity, aggregation, and challenges in micropatterning. Herein, we introduce a refined method that employs a metal-organic framework (MOF) as a precursor combined with direct laser writing. The inherent structure of MOFs ensures a uniform distribution of metal ions and organic linkers, yielding homogeneous MOx/C structures. The laser processing facilitates precise micropatterning (< 2 μm, comparable to typical photolithography) of the MOx/C crystals. The optimized MOF-derived MOx/C sensor rapidly detected ethanol gas even at room temperature (105 and 18 s for response and recovery, respectively), with a broad range of sensing performance from 170 to 3,400 ppm and a high response value of up to 3,500%. Additionally, this sensor exhibited enhanced stability and thermal resilience compared to previous MOF-based counterparts. This research opens up promising avenues for practical applications in MOF-derived sensing devices.

A Triptycene-Based Layered/Flower-Like 2D Conductive Metal-Organic Framework with 3D Extension as an Electrode for Efficient Li Storage

2D metal-organic frameworks (2D MOFs) with π conjugation have attracted widespread attention in the field of lithium storage due to their unique electron transfer units and structural characteristics. However, the periodic 2D planar extension structure hides some active sites, which is not conducive to the utilization of its structural advantages. In this work, a series of triptycene-based 2D conductive MOFs (M-DBH, M = Ni, Mn, and Co) with 3D extension structures are constructed by coordinating 9,10-dihydro-9,10-[1,2]benzenoanthracene-2,3,6,7,14,15-hexaol with metal ions to explore their potential applications in lithium-ion and lithium-sulfur batteries. This is the first study in which 2D conductive MOFs with the 3D extended molecule are used as electrode materials for lithium storage. The designed material generates rich active sites through staggered stacking layers and shows excellent performance in lithium-ion and lithium-sulfur batteries. The capacity retention rate of Ni-DBH can reach over 70% after 500 cycles at 0.2 C in lithium-ion batteries, while the capacity of S@Mn-DBH exceeds 305 mAh g-1 after 480 cycles at 0.5 C in lithium-sulfur batteries. Compared with the materials with 2D planar extended structures, the M-DBH electrodes with 3D extended structures in this work exhibit better performance in terms of cycle time and lithium storage capacity.

Anchoring π-d Conjugated Metal-Organic Frameworks with Dual-Active Centers on Carbon Nanotubes for Advanced Potassium-Ion Batteries

Potassium-ion batteries (PIBs) are gradually gaining attention owing to their natural abundance, excellent security, and high energy density. However, developing excellent organic cathode materials for PIBs to overcome the poor cycling stability and slow kinetics caused by the large radii of K+ ions is challenging. This study demonstrates for the first time the application of a hexaazanonaphthalene (HATN)-based 2D π-d conjugated metal-organic framework (2D c-MOF) with dual-active centers (Cu-HATNH) and integrates Cu-HATNH with carbon nanotubes (Cu-HATNH@CNT) as the cathode material for PIBs. Owing to this systematic module integration and more exposed active sites with high utilization, Cu-HATNH@CNT exhibits a high initial capacity (317.5 mA h g-1 at 0.1 A g-1 ), excellent long-term cycling stability (capacity retention of 96.8% at 5 A g-1 after 2200 cycles), and outstanding rate capacity (147.1 mA h g-1 at 10 A g-1 ). The reaction mechanism and performance are determined by combining experimental characterization and density functional theory calculations. This contribution provides new opportunities for designing high-performance 2D c-MOF cathodes with multiple active sites for PIBs.

Microfluidic-Assisted 3D Printing Zinc Powder Anode with 2D Conductive MOF/MXene Heterostructures for High-Stable Zinc-Organic Battery

Zinc powder (Zn-P) anodes have significant advantages in terms of universality and machinability compared with Zn foil anodes. However, their rough surface, which has a high surface area, intensifies the uncontrollable growth of Zn dendrites and parasitic side reactions. In this study, an anti-corrosive Zn-P-based anode with a functional layer formed from a MXene and Cu-THBQ (MXene/Cu-THBQ) heterostructure is successfully fabricated via microfluidic-assisted 3D printing. The unusual anti-corrosive and strong adsorption of Zn ions using the MXene/Cu-THBQ functional layer can effectively homogenize the Zn ion flux and inhibit the hydrogen evolution reaction (HER) during the repeated process of Zn plating/stripping, thus achieving stable Zn cycling. Consequently, a symmetric cell based on Zn-P with the MXene/Cu-THBQ anode exhibits a highly reversible cycling of 1800 h at 2 mA cm-2 /1 mAh cm-2 . Furthermore, a Zn-organic full battery matched with a 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl organic cathode riveted on graphene delivers a high reversible capacity and maintains a long cycle life.

Synthesis of Electrical Conductive Metal-Organic Frameworks for Electrochemical Applications

Electrical conductivity is very important property of nanomaterials for using wide range of applications especially energy applications. Metal-organic frameworks (MOFs) are notorious for their low electrical conductivity and less considered for usage in pristine forms. However, the advantages of high surface area, porosity and confined catalytic active sites motivated researchers to improve the conductivity of MOFs. Therefore, 2D electrical conductive MOFs (ECMOF) have been widely synthesized by developing the effective synthetic strategies. In this article, we have summarized the recent trends in developing the 2D ECMOFs, following the summary of potential applications in the various fields with future perspectives.

MXene-Based Current Collectors for Advanced Rechargeable Batteries

As an indispensable component of rechargeable batteries, the current collector plays a crucial role in supporting the electrode materials and collecting the accumulated electrical energy. However, some key issues, like uneven resources, high weight percentage, electrolytic corrosion, and high-voltage instability, cannot meet the growing need for rechargeable batteries. In recent years, MXene-based current collectors have achieved considerable achievements due to its unique structure, large surface area, and high conductivity. The related research has increased significantly. Nonetheless, a comprehensive review of this area is seldom. Herein the applications and progress of MXene in current collector are systematically summarized and discussed. Meanwhile, some challenges and future directions are presented.

A Layered Bi2 Te3 @PPy Cathode for Aqueous Zinc-Ion Batteries: Mechanism and Application in Printed Flexible Batteries

Low-cost, safe, and environmental-friendly rechargeable aqueous zinc-ion batteries (ZIBs) are promising as next-generation energy storage devices for wearable electronics among other applications. However, sluggish ionic transport kinetics and the unstable electrode structure during ionic insertion/extraction hamper their deployment. Herein, a new cathode material based on a layered metal chalcogenide (LMC), bismuth telluride (Bi2 Te3 ), coated with polypyrrole (PPy) is proposed. Taking advantage of the PPy coating, the Bi2 Te3 @PPy composite presents strong ionic absorption affinity, high oxidation resistance, and high structural stability. The ZIBs based on Bi2 Te3 @PPy cathodes exhibit high capacities and ultra-long lifespans of over 5000 cycles. They also present outstanding stability even under bending. In addition, here the reaction mechanism is analyzed using in situ X-ray diffraction, X-ray photoelectron spectroscopy, and computational tools and it is demonstrated that, in the aqueous system, Zn2+ is not inserted into the cathode as previously assumed. In contrast, proton charge storage dominates the process. Overall, this work not only shows the great potential of LMCs as ZIB cathode materials and the advantages of PPy coating, but also clarifies the charge/discharge mechanism in rechargeable ZIBs based on LMCs.

Nonplanar π-Conjugated Sulfur Heterocyclic Quinone Polymer Cathode for Air-Rechargeable Zinc/Organic Battery with Simultaneously Boosted Output Voltage, Rate Capability, and Cycling Life

π-conjugated organic compounds with a good charge transfer ability and rich redox functional groups are promising cathode candidates for air-rechargeable aqueous Zn-based batteries (AAZBs). However, the output voltage of even the state-of-the-art π-conjugated organic cathodes lies well below 0.8 V, resulting in insufficient energy density. Herein, we design a nonplanar π-conjugated sulfur heterocyclic quinone polymer (SHQP) as an advanced cathode material for AAZBs by polymerization 1,4-Benzoquinone (BQ) and S heteroatoms periodically. The extended π-conjugated plane and enhanced aromaticity endow SHQP with a more sensitive charge transfer ability and robust structure. Furthermore, the delocalized π electrons in the whole system are insufficient as the π orbit of the S heteroatom is not in the same plane with the π orbit of BQ due to its folded configuration, resulting in negligible variation of electron density around C═O after the polymerization. Thus, the output voltage of SHQP shows no significant decrease even though the thioether bond (-S-) functions as electron donor. Consequently, the Zn/SHQP AAZBs can deliver a record high midpoint discharging voltage (0.95 V), rate performance (119 mAh g-1 at 10 A g-1), and durability (98.7% capacity retention after 200 cycles) across a wide temperature range.

Orientation Control of a Two-Dimensional Conductive Metal-Organic Framework Thin Film by a Pyridine Vapor-Assisted Dry Process

Metal-organic frameworks (MOFs) are attractive materials with periodic pore structures constructed by coordinating metal ions and organic ligands. Recently, Cu3(HHTP)2 (HHTP = 2,3,6,7,10,11-hexahydroxytriphenylene), a two-dimensional conductive MOF, has attracted attention as a promising device material. Owing to the anisotropy of Cu3(HHTP)2 properties, oriented thin films of this MOF are desired for evaluating its physical properties and device integration. To date, wet processes have been used to fabricate Cu3(HHTP)2 films, whereas dry processes are essential for high-quality devices. However, oriented Cu3(HHTP)2 thin films have not yet been fabricated by using dry processes. In this study, we succeed in fabricating an orientation-controlled Cu3(HHTP)2 film on Al2O3 (001) by using a two-step dry process involving (1) the multilayer deposition of copper acetate and HHTP using a vapor deposition system and (2) pyridine vapor-assisted annealing. In-plane and out-of-plane X-ray diffraction patterns confirm the successful fabrication of the (001)-oriented Cu3(HHTP)2 films. The conductivity evaluated by four-probe measurements is 2.6 × 10-2 S cm-1, comparable to that of films fabricated by wet processes. This study provides a novel guideline for the orientation control of two-dimensional conductive MOF thin films via a dry process.

Fiber Integrated Metal-Organic Frameworks as Functional Components in Smart Textiles

Owing to high modularity and synthetic tunability, metal-organic frameworks (MOFs) on textiles are poised to contribute to the development of state-of-the-art wearable systems with multifunctional performance. While these composite materials have demonstrated promising functions in sensing, filtration, detoxification, and biomedicine, their applicability in multifunctional systems is only beginning to materialize. This review highlights the multifunctionality and versatility of MOF-integrated textile systems. It summarizes the operational goals of MOF@textile composites, encompassing sensing, filtration, detoxification, drug delivery, UV protection, and photocatalysis. Building upon these recent advances, this review concludes with an outlook on emerging opportunities for the diverse applications of MOF@textile systems in the realm of smart wearables.

Ligand-Oxidation-Based Anodic Synthesis of Oriented Films of Conductive M-Catecholate Metal-Organic Frameworks with Controllable Thickness

Effective control over the crystallization of metal-organic framework (MOF) films is of great importance not only for the performance study and optimization in related applications but also for the fundamental understanding of the involved reticular chemistry. Featuring many technological advantages, electrochemical synthesis has been extensively reported for many MOF materials but is still challenged by the production of dense oriented films with a large-range tuning of thickness. Here, we report a ligand-oxidation-based anodic strategy capable of synthesizing oriented films of two-dimensional (2D) and three-dimensional (3D) conductive M-catecholate MOFs (2D Cu3(HHTP)2, 2D Zn3(HHTP)2, 2D Co3(HHTP)2, 3D YbHHTP, and 2D Cu2TBA) with tunable thicknesses up to tens of micrometers on commonly used electrodes. This anodic strategy relies on the oxidation of redox-active catechol ligands and follows a stepwise electrochemical-chemical reaction mechanism to achieve effective control over crystallizing M-catecholate MOFs into films oriented in the [001] direction. Benefiting from the electrically conductive nature, Cu3(HHTP)2 films could be thickened at a steady rate (17.4 nm·min-1) from ∼90 nm to 10.7 μm via a growth mechanism differing from those adopted in previous electrochemical synthesis of dense MOF films with limited thickness due to the self-inhibition effect. This anodic synthesis could be further combined with a templating strategy to fabricate not only films with well-defined 2D features in sizes from micrometers to millimeters but also high aspect ratio mesostructures, such as nanorods, of Cu3(HHTP)2.

Expanding the horizons of porphyrin metal-organic frameworks via catecholate coordination: exploring structural diversity, material stability and redox properties

Porphyrin based Metal-Organic Frameworks (MOFs) have generated high interest because of their unique combination of light absorption, electron transfer and guest adsorption/desorption properties. In this study, we expand the range of available MOF materials by focusing on the seldom studied porphyrin ligand H10TcatPP, functionalized with tetracatecholate coordinating groups. A systematic evaluation of its reactivity with M(iii) cations (Al, Fe, and In) led to the synthesis and isolation of three novel MOF phases. Through a comprehensive characterization approach involving single crystal and powder synchrotron X-ray diffraction (XRD) in combination with the local information gained from spectroscopic techniques, we elucidated the structural features of the solids, which are all based on different inorganic secondary building units (SBUs). All the synthesized MOFs demonstrate an accessible porosity, with one of them presenting mesopores and the highest reported surface area to date for a porphyrin catecholate MOF (>2000 m2 g-1). Eventually, the redox activity of these solids was investigated in a half-cell vs. Li with the aim of evaluating their potential as electrode positive materials for electrochemical energy storage. One of the solids displayed reversibility during cycling at a rather high potential (∼3.4 V vs. Li+/Li), confirming the interest of redox active phenolate ligands for applications involving electron transfer. Our findings expand the library of porphyrin-based MOFs and highlight the potential of phenolate ligands for advancing the field of MOFs for energy storage materials.

Breaking the photoswitch speed limit

The forthcoming generation of materials, including artificial muscles, recyclable and healable systems, photochromic heterogeneous catalysts, or tailorable supercapacitors, relies on the fundamental concept of rapid switching between two or more discrete forms in the solid state. Herein, we report a breakthrough in the "speed limit" of photochromic molecules on the example of sterically-demanding spiropyran derivatives through their integration within solvent-free confined space, allowing for engineering of the photoresponsive moiety environment and tailoring their photoisomerization rates. The presented conceptual approach realized through construction of the spiropyran environment results in ~1000 times switching enhancement even in the solid state compared to its behavior in solution, setting a record in the field of photochromic compounds. Moreover, integration of two distinct photochromic moieties in the same framework provided access to a dynamic range of rates as well as complementary switching in the material's optical profile, uncovering a previously inaccessible pathway for interstate rapid photoisomerization.

From a Collapse-Prone, Insulating Ni-MOF-74 Analogue to Crystalline, Porous, and Electrically Conducting PEDOT@MOF Composites

Electrically conductive porous metal-organic frameworks (MOFs) show great promise in helping advance electronics and clean energy technologies. However, large porosity usually hinders long-range charge transport, an essential criterion of electrical conductivity, underscoring the need for new strategies to combine these two opposing features and realize their diverse potentials. All previous strategies to boost the conductivity of porous MOFs by introducing redox-complementary guest molecules, conducting polymers, and metal nanoparticles have led to a significant loss of frameworks' porosity and surface areas, which could be otherwise exploited to capture additional guests in electrocatalysis and chemiresistive sensing applications. Herein, we demonstrate for the first time that the in situ oxidative polymerization of preloaded 3,4-ethylenedioxythiophene (EDOT) monomers into the polyethylenedioxythiophene (PEDOT) polymer inside the hexagonal cavities of an intrinsically insulating Ni2(NDISA) MOF-74 analogue (NDISA = naphthalenediimide N,N-disalicylate), which easily collapses and becomes amorphous upon drying, simultaneously enhanced the crystallinity, porosity, and electrical conductivity of the resulting PEDOT@Ni2(NDISA) composites. At lower PEDOT loading (∼22 wt %), not only did the Brunauer-Emmett-Teller surface area of the PEDOT@Ni2(NDISA) composite (926 m2/g) more than double from that of evacuated pristine Ni2(NDISA) (387 m2/g), but also its electrical conductivity (1.1 × 10-5 S/cm) soared 105 times from that of the pristine MOF, demonstrating unprecedented dual benefits of our strategy. At higher PEDOT loading (≥33 wt %), the electrical conductivity of Ni2(NDISA)⊃PEDOT composites further increased modestly (10-4 S/cm), but their porosity dropped precipitously as large amounts of PEDOT filled up the hexagonal MOF channels. Thus, our work presents a simple new strategy to simultaneously boost the structural stability, porosity, and electrical conductivity of intrinsically insulating and collapse-prone MOFs by introducing small amounts of conducting polymers that can not only reinforce the MOF scaffolds and prevent them from collapsing but also help create a much coveted non-native property by providing charge carriers and charge transport pathways.