3D covalent organic framework membrane with fast and selective ion transport

Recent Advances in the Application of Covalent Organic Framework-Based Ionic Conductors in Proton Exchange Membrane Fuel Cells

Covalent organic frameworks (COFs), known for their tunable porosity and functional versatility, have demonstrated exceptional ionic conductivity in proton exchange membrane fuel cells (PEMFCs). This review summarizes recent advancements in COF-based materials for PEMFC applications, emphasizing their roles as intrinsic proton conductors, host matrices for proton carriers, and additives in composite ionomers/membranes. Key strategies such as pore engineering, functional group modification, and hybrid designs with polymers are analyzed to highlight their influence on proton conductivity and mechanical stability. Recent developments reveal that functionalized COFs can achieve proton conductivities exceeding 0.89 S cm-1 at 90 °C under 100% relative humidity (RH), comparable to commercial Nafion membranes. Additionally, COF-modified ionomers applied to catalyst layers have enabled fuel cells to achieve peak power densities 1.6 times higher than those without COF incorporation. Despite these advancements, challenges persist in terms of membrane durability, scalability, and performance under low humidity or high-temperature conditions. Future research should prioritize structural optimization, interfacial compatibility, and cost-effective synthesis methods to fully realize the potential of COFs in next-generation PEMFCs. This review underscores the transformative potential of COFs in addressing the critical limitations of traditional proton-conducting materials, paving the way for innovative solutions in fuel cell technology.

Hydrogen Bond Network Assisted Ultrafast Ion Transport of Anion Exchange Membrane Grafting with Covalent Organic Frameworks for Hydrogen Conversion

The development of anion exchange membranes (AEMs) capable of facilitating rapid hydroxide ion transport, while maintaining robust mechanical stability, is considered a key direction for advancing hydrogen energy conversion systems. Herein, we synthesized a series of AEMs by grafting covalent organic frameworks (COFs) onto triphenylpiperidine copolymer and systematically evaluated the performance of AEMs. The tailored COFs, characterized by an extensive hydrogen bond network and high micro-porosity, created interconnected high-speed ion transport channels, significantly reducing the resistance to hydroxide ion conduction. Remarkably, the COF-grafted membranes exhibited superior ionic conductivity compared to pristine triphenylpiperidine, even at lower ion exchange capacities. Additionally, the crystalline and highly rigid structure of the grafted COFs effectively preserved the mechanical stability of the membranes. The optimized COF-grafted AEMs demonstrated outstanding performance, achieving a peak power density of 1.54 W cm-2 in H2-O2 fuel cells and exceptional current densities of 4.5 A cm-2 at 2.0 V in 1 m KOH and 1.1 A cm-2 at 2.0 V in pure water at 80 °C. The present work provides an effective strategy for enhancing AEM performance through the grafting of COFs.

One-step microbial cultivated bacterial cellulose membrane with 1D/2D nanochannels for efficient osmotic energy conversion

Osmotic energy conversion based on bio-inspired layered membranes has garnered significant interest. However, traditional biomass ion-selective membranes suffer from complex preparation, uneconomic nature, poor selectivity, and low power density. Here, we introduce scalable one-step in situ culture for nanofluidic membrane materials (GO/C-BC) composed of graphene oxide (GO), carboxymethyl cellulose sodium salt (CMC), and bacterial cellulose (BC). This preparation method effectively combines 1D and 2D nanochannels, reduces membrane resistance, and increases power density. The GO1.5/C-BC membrane exhibits excellent cation selectivity (0.89), achieving energy conversion efficiency of 31.40 % and delivering a power density of 7.49 W m-2 under a 500-fold concentration gradient. Stability tests under artificial seawater and river water conditions show only a 4.44 % decrease in power density after 20 d, highlighting its excellent stability and durability. Moreover, by connecting 28 power units in series, the membrane can produce a voltage output of -4 V. This scalable and environmentally friendly biomass material presents new avenues for osmotic energy conversion.

Visual Engineering Achieved with Electronegative Carbon Dots for Highly Efficient Ion Flux Regulation

Various modification methods for lithium-metal battery separators have been well explored in the past decades, among which the most common process is to coat modified slurries onto the separators by blade-coating method. However, the distribution of the slurries is often non-uniform in this process, while the uniformity usually needs to be detected by electron microscope, which is time and cost-consuming. To solve this long-standing technical issue, it focuses on the "visualization" of modification effect with negatively charged carbon dots under UV light, and deeply investigates the ion transport problem caused by the non-uniform material modification. With this unique "visual engineering" strategy, uniform separator can be easily detected, which further allows for the construction of a uniform negative shielding layer and cation channels. It accelerates the ion transport process, realizes a stable Li stripping and deposition process, and avoids dendrite growth. To this end, in symmetric batteries with different electrolyte compositions, stable operation of 1200 h can be achieved. In addition, negatively charged polysulfide shuttles can be greatly suppressed, thus avoiding the infamous "shuttle effect" in lithium-sulfur batteries. This work provides a new avenue for screening well-modified separators through "visual engineering", further accelerating the practical application of series of rechargeable batteries.

Creating Sodium Ion Channels via De Novo Encapsulation of Ionophores for Enhanced Water Energy Harvesting

Biological ion channels achieve remarkable permselectivity and cation discrimination through the synergy of their intricate architectures and specialized ionophores within confined nanospaces, enabling efficient energy conversion. Emulating such selectivity in synthetic nanochannels, however, remains a persistent challenge. To address this, a novel host-guest assembly membrane is developed by incorporating sodium-selective ionophores into a β-ketoenamine-linked covalent organic framework (COF). This design confers exceptional permselectivity and Na+ selectivity, achieving Na+/K+ and Na+/Li+ selectivity ratios of 3.6 and 103, respectively, along with near-perfect Na+/Cl- selectivity under a 0.5 M || 0.01 M salinity gradient. Notably, the membrane dynamically switches its permselectivity to favor anion transport in the presence of high-valent cations (e.g., Ca2+), overcoming limitations such as uphill cation diffusion and back currents observed in conventional cation-selective membranes. This adaptive behavior yields a 4.6-fold increase in output power density in Ca2+-rich environments. These findings advance the design of biomimetic nanochannels with unparalleled ion selectivity and enhanced energy conversion efficiency.

Advanced Microporous Framework Membranes for Sustainable Separation

Advancements in membrane-based separation hinge on the design of materials that transcend conventional limitations. Microporous materials, including metal-organic frameworks (MOFs), covalent-organic frameworks (COFs), macrocycles, and porous organic cages (POCs) offer unprecedented control over pore architecture, chemical functionality, and transport properties, making them promising candidates for next-generation membrane technologies. The well-defined and tunable micropores provide a pathway to directly address the permeability-selectivity trade-off inherent in conventional polymer membranes. Here, this review explores the latest advancements in these four representative microporous membranes, emphasizing their breakthroughs in hydrocarbon separation, liquid-phase molecular sieving, and ion-selective transport, particularly focusing on their structure-performance relationships. While their tailored structures enable exceptional performance, practical adoption requires overcoming hurdles in scalability, durability, and compatibility with industrial processes. By offering insights into membrane structure optimization and innovative design strategies, this review provides a roadmap for advancing microporous membranes from laboratory innovation to real-world implementation, ultimately supporting global sustainability goals through energy-efficient separation processes.

Plasmonic Ion Diode Membrane (PIDM) for Enhanced Nanofluidic Ion Transport

Efficient applications of nanofluidic devices are often limited by the insufficient ion permselectivity and inherent ion concentration polarization (ICP) phenomenon. In this work, a bio-inspired plasmonic ion diode membrane (PIDM) was designed and fabricated for enhanced ion transport and osmotic energy harvesting by integrating covalent organic frameworks (COFs) and three-dimensional Au nanoparticles (3D AuNPs) into anode aluminum oxide (AAO). Under light irradiation, localized surface plasmon resonance (LSPR) excitation of 3D AuNPs can release huge plasmonic heat and produce abundant hot charge carriers (hot electrons and holes) simultaneously. The former heats the solution and generates a thermal gradient for boosting ion flux, while the latter transfers to the COFs layer, increasing charge density for promoting ion permselectivity. Importantly, it has been found that different COFs with varied pore sizes and charges have an obvious influence on energy harvesting efficiency. Under the optimum condition, a high output power density of 65.7 W m-2 in a 500-fold concentration gradient could be achieved. This work provides a practical and efficient way to boost ion transport and enhance osmotic energy conversion by utilizing the synergistic effect of plasmonics and ion diode (ID) property.

Engineering 4-Connecting 3D Covalent Organic Frameworks with Oriented Li+ Channels for High-Performance Solid-State Electrolyte in Lithium Metal Battery

The development of rapid and stable ion-conductive channels is pivotal for solid-state electrolytes (SSEs) in achieving high-performance lithium metal batteries (LMBs). Covalent organic frameworks (COFs) have emerged as promising Li-ion conductors due to their well-defined channel architecture, facile chemical tunability, and mechanical robustness. However, the limited active sites and restricted segmental motion for Li+ migration significantly impede their ionic conductivity. Herein, a rational design strategy is presented to construct 3D porous COF frameworks (TP-COF and TB-COF) using linear ditopic monomers connected via C─C and C─N linkages. These COFs, integrated with polymer electrolytes, provide enhanced Li+ transport pathways and stabilize lithium anodes in LMBs. The TB-COF, featuring larger pore apertures and abundant ─C═N─ active sites, facilitates superior Li+ conduction (8.89 × 10-4 S cm-1) and a high transference number (0.80) by enhancing lithium salt dissolution. LiF/Li3N-rich SEI enables uniform Li deposition, enabling PEO-TB-COF SSEs to achieve >1000 h stability at 1 mA cm⁻2 while retaining 90% capacity through 800 cycles (0.5 C) in LFP||Li cells. Molecular dynamics simulations and COMSOL Multiphysics modeling reveal that extended Li+ transport channels and reduced interfacial diffusion barriers are key to enhanced performance.

Three-Dimensional Covalent Organic Framework for Efficient Hydrogen Storage through Polarization-Wall Engineering

Covalent organic frameworks (COFs), characterized by high surface areas and tunable pore structures/environments, are regarded as a promising alternative to physisorption H2 storage materials. However, their interaction with hydrogen is often too weak, necessitating the exploration of strategies to enhance sorption heat. Herein, we strengthened the adsorption induction of COF on H2 through a polarized wall engineering. The fluorine groups on the pore wall of three-dimensional COFs polarize their surrounding regions, resulting in high sorption heat sites. Due to the enhanced H2 sorption heat, the total H2 uptake of 3D-F-COF is up to to 5.96 wt % at 77 K and 90 bar. Moreover, the H2 adsorption enhancement effect of the polar group does not involve chemisorption, and the material exhibits excellent cycling stability. These results reveal that modulating the H2 sorption heat by incorporating polar groups is a promising strategy for achieving efficient H2 storage in porous materials.

High-Efficiency Ion Transport in Ultrathin 3D Covalent Organic Framework Nanofluidics

High-efficiency ion transport is essential for both biological and nonbiological processes, including the regulation of cell homeostasis, energy conversion, and mass transfer in chemical industry. Nanofluidic channels are considered ideal platforms for delicate control of ion transport in their unique nanoconfinement, yet currently reported 1D and 2D nanofluidics are subjected to elevated transport resistance due to discontinuous and random channels. Here, we engineer ultrathin, 3D covalent organic framework (3D-COF) nanofluidics featuring continuously interpenetrated pathways and well-ordered pore arrangements, demonstrating superior ion conductance. The energy barrier for ion transport across 3D-COF nanofluidics is exceptionally low, suggesting ultrafast and low-resistance ion movements. Theoretical calculations indicate that 3D-COF nanofluidics facilitate group adsorption to anions, leading to high energy barriers for anion mobility, thus enhancing ion selectivity and high-throughput cation transport. In osmotic energy applications, 3D-COF nanofluidics achieve a power density of 217.7 W m-2 with artificial seawater and river water, potentially scalable to 1238.2 W m-2 under a 500-fold salinity gradient. The proposed 3D-COF nanofluidics offer new avenues for desalination and ion/molecular separation.

Dehydration-enhanced Ion Recognition of Triazine Covalent Organic Frameworks for High-resolution Li+/Mg2+ Separation

The precise and rapid extraction of lithium from salt-lake brines is critical to meeting the global demand for lithium resources. However, it remains a major challenge to design ion-transport membranes with accurate recognition and fast transport path for the target ion. Here, we report a triazine covalent organic framework (COF) membrane with high resolution for Li+ and Mg2+ that enables fast Li+ transport while almost completely inhibiting Mg2+ permeation. The remarkably high rejection of Mg2+ by the COF membrane is achieved via imposed ion dehydration and the construction of the energy well. The proper hydrophilic environment of the COF channel promotes the dissociation of Li+ from the negatively charged functional groups, allowing Li+ for hopping transport supported by the sulfonate side-chains to shorten the diffusion path of Li+. Under high-salinity electrodialysis conditions, the COF membrane demonstrates robust Li+/Mg2+ separation performance (No Mg2+ were detected in the collected solution), achieving efficient lithium recovery and high product purity (Li2CO3: 99.3 %). This membrane design strategy enables high energy efficiency and powerful lithium extraction in the electrodialysis lithium extraction process, and can be generalized to other energy and separation related membranes.

Molecular Design of Positively Charged 3D Covalent-Organic Framework Membranes for Li+/Mg2+ Separation

3D covalent-organic framework (3D COF) membranes have unique features such as smaller pore sizes and more interconnected networks compared with 2D COF counterparts. However, the complicated and unmanageable fabrication hinders their rapid development. Molecular simulation, which can efficiently explore the structure-performance relationship of membranes, holds great promise in accelerating the development of 3D COF membranes. In this study, a series of 3D-COF membranes (TFPM-Pa-X) is designed with different charge densities (fully charged, partially charged, and neutral) and interpenetration numbers (2-, 3-, 4-, and 5-fold), subsequently investigate their contributions to Li+/Mg2+ separation through molecular simulation. Membrane morphology and pore size are found to strongly depend on the charged density and interpenetration number. The pore size and Cl- ion density play a crucial role in governing membrane separation performance. TFPM-Pa-X membrane with a smaller interpenetration number and a higher charge density promotes Li+/Mg2+ separation. The fully charged 2-fold interpenetrated membrane has superior performance in breaking the trade-off between the flux of Li+ (JLi +) and the selectivity of Li+ over Mg2+ (SLi + /Mg 2+). This study may facilitate the rational design of new 3D COF membranes for high-performance ion separation.

Transforming 2D Imine into 3D Thiazole Covalent Organic Frameworks by Conjugated Connectors: Fully Conjugated Photocatalysts

We developed a robust three-dimensional (3D) covalent organic framework (COF), fully conjugated in both the planar (x, y) and interlayer (z) directions, using a one-pot sulfurization process. We converted the two-dimensional (2D) imine-linked COF (Py-BDA-COF) to the 3D thiazole-linked COF (3D-Py-BDA-S-COF). In the interlayer direction (z-axis), the alternating covalently bound acetylene and ethylene arrangements serve as conjugated connectors ("pillars") and create a fully conjugated and very robust COF in all three dimensions. On top of this, the presence of the sulfur lone pair electrons in the thiazole rings considerably enhances the electron delocalization degree of the frameworks. The 3D-Py-BDA-S-COF is successfully evaluated in the photocatalytic reduction of nitrobenzene.

A Mechanically Robust, Extreme Environment-Stable, and Fast Ion Transport Nanofluidic Fiber

Constructing mechanically strong and environmentally stable nanofluidic fibers with excellent ion transport remains a challenge. Herein, we design a mechanically robust and stable aramid nanofiber/carboxylated aramid nanofiber (ANF/cANF) hybrid nanofluidic fiber with a high ionic conductivity via a wet spinning-induced orientation strategy. Benefiting from the oriented structure and strong interfacial interactions of the filaments, the ANF/cANF nanofluidic fiber exhibits a high tensile strength of 276.8 MPa. Carboxylation and oriented nanochannels dramatically reduce the charge transfer resistance, resulting in a high ionic conductivity. As a result, the ANF/cANF nanofluidic fiber obtains a 5-fold increase in ionic conductivity compared to that of the disordered fiber. Notably, the nanofluidic fiber maintains its structural integrity and mechanical properties after 90 days of immersion in water. Additionally, it retains its favorable surface-charge-dominated ion transport capabilities even under extreme conditions, including exposure to acids, alkalis, and ethanol, as well as after treatments at high (150 °C) and low (-196 °C) temperatures.

Ultrathin Azine Covalent Organic Framework Membrane for Highly-Efficient Nanofluidic Osmotic Energy Generator

Charged covalent organic framework (COF) membranes have gained wide interest as the key component in the reverse electrodialysis technique to harness salinity energy. However, maintaining rapid ion transport and high selectivity in a Ca2+-rich environment remains a formidable challenge. Herein, a highly cation-conductive azine COF membrane is synthesized via a layer-by-layer chemical reaction between 2,4-dihydroxy-1,3,5-diphenyltrialdehyde (DHTA) and hydrazine hydrate (HZ). The osmotic energy generator based on this membrane delivers a high power density of 17.8 W m-2 under 2.5 M/0.05 M CaCl2, outperforming the TFP-HZ membrane (3.2 W m-2), commercial benchmark (5 W m-2), and other literature reported membranes owing to the simultaneous modulation of charges in angstrom scale channels and selective layer thickness. Moreover, this osmotic power density is comparable to that in a NaCl gradient (2.5 M/0.05 M, 16.9 W m-2), which is rare. These results indicate that the DHTA-HZ membrane is highly suitable for application in hypersaline environments containing Ca2+, serving as an inspiration for the development of COF-based nanofluidic membranes with high power output efficiency in a practical high-salinity environment.

Functionalized Separators Boosting Electrochemical Performances for Lithium Batteries

The growing demands for energy storage systems, electric vehicles, and portable electronics have significantly pushed forward the need for safe and reliable lithium batteries. It is essential to design functional separators with improved mechanical and electrochemical characteristics. This review covers the improved mechanical and electrochemical performances as well as the advancements made in the design of separators utilizing a variety of techniques. In terms of electrolyte wettability and adhesion of the coating materials, we provide an overview of the current status of research on coated separators, in situ modified separators, and grafting modified separators, and elaborate additional performance parameters of interest. The characteristics of inorganics coated separators, organic framework coated separators and inorganic-organic coated separators from different fabrication methods are compared. Future directions regarding new modified materials, manufacturing process, quantitative analysis of adhesion and so on are proposed toward next-generation advanced lithium batteries.

Self-Organized Protonic Conductive Nanochannel Arrays for Ultra-High-Density Data Storage

While the highest-performing memristors currently available offer superior storage density and energy efficiency, their large-scale integration is hindered by the random distribution of filaments and nonuniform resistive switching in memory cells. Here, we demonstrate the self-organized synthesis of a type of two-dimensional protonic coordination polymers with high crystallinity and porosity. Hydrogen-bond networks containing proton carriers along its nanochannels enable uniform resistive switching down to the subnanoscale range. Leveraging such nanochannel arrays, we achieve logic operations of graphical gate circuits with negligible leakage and sneak path currents over areas ranging from 0.5 μm × 0.5 μm to 20 nm × 20 nm, providing the smallest building blocks to date for large-scale integration. The nonvolatile resistive switching exhibits high mobility (∼0.309 cm2 V-1 s-1), a large on/off ratio (∼103), and ultrahigh-density data storage (∼645 Tbit/in2), even within a trilayer (∼4.01 nm). An ultrahigh-precision artificial retina with integrated convolutional neural network calculations is demonstrated, enabling facial and color recognition capabilities.

Turing-type nanochannel membranes with extrinsic ion transport pathways for high-efficiency osmotic energy harvesting

Two-dimensional (2D) nanofluidic channels with confined transport pathways and abundant surface functional groups have been extensively investigated to achieve osmotic energy harvesting. However, solely relying on intrinsic interlayer channels results in insufficient permeability, thereby limiting the output power densities, which poses a significant challenge to the widespread application of these materials. Herein, we present a nanoconfined sacrificial template (NST) strategy to create a crafted channel structure, termed as Turing-type nanochannels, within the membrane. Extrinsic interlaced channels are formed between the lamellae using copper hydroxide nanowires as sacrificial templates. These Turing-type nanochannels significantly increase transport pathways and functional areas, resulting in a 23% enhancement in ionic current while maintaining a cation selectivity of 0.91. The output power density of the Turing-type nanochannel membrane increases from 3.9 to 5.9 W m-2 and remains stable for at least 120 hours. This membrane exhibits enhanced applicability in real saltwater environments across China, achieving output power densities of 7.7 W m-2 in natural seawater and 9.8 W m-2 in salt-lake brine. This work demonstrates the promising potential of the Turing-channel design for nanoconfined ionic transport in the energy conversion field.

Modular Customized Biomimetic Nanofluidic Diode for Tunable Asymmetric Ion Transport

Artificial ion diodes, inspired by biological ion channels, have made significant contributions to the fields of physics, chemistry, and biology. However, constructing asymmetric sub-nanofluidic membranes that simultaneously meet the requirements of easy fabrication, high ion transport efficiency, and tunable ion transport remains a challenge. Here, a direct and flexible in situ staged host-guest self-assembly strategy is employed to fabricate ion diode membranes capable of achieving zonal regulation. Coupling the interfacial polymerization process with a host-guest assembly strategy, it is possible to easily manipulate the type, order, thickness, and charge density of each module by introducing two oppositely charged modules in stages. This method enables the tuning of ion transport behavior over a wide range salinity, as well as responsive to varying pH levels. To verify the potential of controllable diode membranes for application, two ion diode membranes with different ion selectivity and high charge density are coupled in a reverse electrodialysis device. This resulted in an output power density of 63.7 W m-2 at 50-fold NaCl concentration gradient, which is 12 times higher than commercial standards. This approach shows potential for expanding the variety of materials that are appropriate for microelectronic power generation devices, desalination, and biosensing.

Recent advances and applications of ionic covalent organic frameworks in food analysis

Ionic covalent organic frameworks with both crystallinity and charged sites have attracted significant attention from the scientific community. The versatile textural structures, precisely defined channels, and abundant charged sites of ionic COFs offer immense potential in various areas such as separation, sample pretreatment, ion conduction mechanisms, sensing applications, catalytic reactions, and energy storage systems. This review presents a comprehensive overview of facile preparation methods for ionic covalent organic frameworks (iCOFs), along with their applications in food sample pretreatment techniques such as solid-phase extraction (SPE), magnetic solid-phase extraction (MSPE), and dispersive solid-phase extraction (DSPE). Furthermore, it highlights the extensive utilization of iCOFs in detecting various food contaminants including pesticides, contaminants from food packaging, veterinary drugs, perfluoroalkyl substances, and poly-fluoroalkyl substances. Specifically, this review critically discusses the limitations, challenges, and future prospects associated with employing iCOF materials to ensure food safety.

Microporous Materials in Polymer Electrolytes: The Merit of Order

Solid-state batteries (SSBs) have garnered significant attention in the critical field of sustainable energy storage due to their potential benefits in safety, energy density, and cycle life. The large-scale, cost-effective production of SSBs necessitates the development of high-performance solid-state electrolytes. However, the manufacturing of SSBs relies heavily on the advancement of suitable solid-state electrolytes. Composite polymer electrolytes (CPEs), which combine the advantages of ordered microporous materials (OMMs) and polymer electrolytes, meet the requirements for high ionic conductivity/transference number, stability with respect to electrodes, compatibility with established manufacturing processes, and cost-effectiveness, making them particularly well-suited for mass production of SSBs. This review delineates how structural ordering dictates the fundamental physicochemical properties of OMMs, including ion transport, thermal transfer, and mechanical stability. The applications of prominent OMMs are critically examined, such as metal-organic frameworks, covalent organic frameworks, and zeolites, in CPEs, highlighting how structural ordering facilitates the fulfillment of property requirements. Finally, an outlook on the field is provided, exploring how the properties of CPEs can be enhanced through the dimensional design of OMMs, and the importance of uncovering the underlying "feature-function" mechanisms of various CPE types is underscored.

Nanoarchitectonics in Advanced Membranes for Enhanced Osmotic Energy Harvesting

Osmotic energy, often referred to as "blue energy", is the energy generated from the mixing of solutions with different salt concentrations, offering a vast, renewable, and environmentally friendly energy resource. The efficacy of osmotic power production considerably relies on the performance of the transmembrane process, which depends on ionic conductivity and the capability to differentiate between positive and negative ions. Recent advancements have led to the development of membrane materials featuring precisely tailored ion transport nanochannels, enabling high-efficiency osmotic energy harvesting. In this review, ion diffusion in confined nanochannels and the rational design and optimization of membrane architecture are explored. Furthermore, structural optimization of the membrane to mitigate transport resistance and the concentration polarization effect for enhancing osmotic energy harvesting is highlighted. Finally, an outlook on the challenges that lie ahead is provided, and the potential applications of osmotic energy conversion are outlined. This review offers a comprehensive viewpoint on the evolving prospects of osmotic energy conversion.

Unipolar Ionic Diode Nanofluidic Membranes Enabled by Stepped Mesochannels for Enhanced Salinity Gradient Energy Harvesting

Developing ionic diode membranes featuring asymmetric structures is in high demand for salinity gradient energy harvesting. These membranes offer benefits in mitigating ion concentration polarization, thereby promoting ion permeability. However, most reported works focus on the role of heterogeneous charge-based bipolar ionic diode membranes for ion concentration polarization suppression, with comparatively less attention given to maintaining ion selectivity. Herein, unipolar ionic diode nanofluidic mesoporous silica membranes featuring stepped mesochannels were developed via a micellar sequential oriented interfacial self-assembly strategy as a salinity gradient energy harvester. Due to the asymmetric mesochannels and unipolar structure (both sides carry negative charge), the ionic diode membranes exhibit a strong rectification ratio of ∼15.91 to facilitate unidirectional ion transport while maintaining excellent cation selectivity (cation transfer number of ∼0.85). Besides, the vertically aligned mesochannels significantly reduce ion transport resistance, generating a high ionic flux. Consequently, the unipolar ionic diode nanofluidic membranes demonstrate a power output of 5.88 W/m2 between artificial sea and river water. The unipolar feature gives notable enhancements of 296% and 144% in power output compared to the symmetric membrane and bipolar ionic diode membrane, respectively. This work opens up new routes for designing ionic diode membranes for salinity gradient energy harvesting.

TRPM4-Inspired Polymeric Nanochannels with Preferential Cation Transport for High-Efficiency Salinity-Gradient Energy Conversion

Biological ion channels exhibit switchable cation transport with ultrahigh selectivity for efficient energy conversion, such as Ca2+-activated TRPM4 channels tuned by cation-π interactions, but achieving an analogous highly selective function is challenging in artificial nanochannels. Here, we design a TRPM4-inspired cation-selective nanochannel (CN) assembled by two poly(ether sulfone)s, respectively, with sulfonate acid and indole moieties, which act as cation-selective activators to manage Na+/Cl- selectivity via ionic and cation-π interactions. The cation selectivity of CNs can be activated by Na+, and thereby the Na+ transference number significantly improves from 0.720 to 0.982 (Na+/Cl- selectivity ratio from 2.6 to 54.6) under a 50-fold salinity gradient, surpassing the K+ transference number (0.886) and Li+ transference number (0.900). The TRPM4-inspired nanochannel membrane enabled a maximum output power density of 5.7 W m-2 for salinity-gradient power harvesting. Moreover, a record energy conversion efficiency of up to 46.5% is provided, superior to most nanochannel membranes (below 30%). This work proposes a novel strategy to biomimetic nanochannels for highly selective cation transport and high-efficiency salinity-gradient energy conversion.

Ionic Liquid Crystal-Polymer Composite Electromechanical Actuators: Design of Two-Dimensional Molecular Assemblies for Efficient Ion Transport and Effect of Electrodes on Actuator Performance

We present the development of free-standing ionic liquid crystal-polymer composite electrolyte films aimed at achieving high-frequency response electromechanical actuators. Our approach entails designing novel layered ionic liquid-crystalline (LC) assemblies by complexing a mesomorphic dimethylphosphate with either a lithium salt or a room-temperature ionic liquid through the formation of ion-dipole interactions or hydrogen bonds. These electrolytes, exhibiting room-temperature ionic conductivities on the order of 10-4 S cm-1 and wide LC temperature ranges up to 77 °C, were successfully integrated into porous polymer networks. We systematically investigated the impact of ions and electrodes on the performance of ionic electroactive actuators. Specifically, the Li+-based liquid crystal-polymer composite actuator with PEDOT:PSS electrodes demonstrated the highest bending deformation, achieving a strain of 0.68% and exhibiting a broad frequency response up to 110 Hz, with a peak-to-peak displacement of 3 μm. In contrast, the ionic-liquid-based liquid crystal-polymer composite actuator with active carbon electrodes showcased a bending response at a maximum frequency of 50 Hz and a force generation of 0.48 mN, without exhibiting the back relaxation phenomenon. These findings offer valuable insights for advancing high-performance electromechanical systems with applications ranging from soft robotics to haptic interfaces.

Ionic Covalent Organic Frameworks in Adsorption and Catalysis

The ion extraction and electro/photo catalysis are promising methods to address environmental and energy issues. Covalent organic frameworks (COFs) are a class of promising template to construct absorbents and catalysts because of their stable frameworks, high surface areas, controllable pore environments, and well-defined catalytic sites. Among them, ionic COFs as unique class of crystalline porous materials, with charges in the frameworks or along the pore walls, have shown different properties and resulting performance in these applications with those from charge-neutral COFs. In this review, current research progress based on the ionic COFs for ion extraction and energy conversion, including cationic/anionic materials and electro/photo catalysis is reviewed in terms of the synthesis strategy, modification methods, mechanisms of adsorption and catalysis, as well as applications. Finally, we demonstrated the current challenges and future development of ionic COFs in design strategies and applications.

Ultrathin Free-Standing Porous Aromatic Framework Membranes for Efficient Anion Transport

Porous aromatic frameworks (PAFs) show promising potential in anionic conduction due to their high stability and customizable functionality. However, the insolubility of most PAFs presents a significant challenge in their processing into membranes and subsequent applications. In this study, continuous PAF membranes with adjustable thickness were successfully created using liquid-solid interfacial polymerization. The rigid backbone and the stable C-C coupling endow PAF membrane with superior chemical and dimensional stabilities over most conventional polymer membranes. Different quaternary ammonium functionalities were anchored to the backbone through flexible alkyl chains with tunable length. The optimal PAF membrane exhibited an OH- conductivity of 356.6 mS ⋅ cm-1 at 80 °C and 98 % relative humidity. Additionally, the PAF membrane exhibited outstanding alkaline stability, retaining 95 % of its OH- conductivity after 1000 hours in 1 M NaOH. To the best of our knowledge, this is the first application of PAF materials in anion exchange membranes, achieving the highest OH- conductivity and exceptional chemical/dimensional stability. This work provides the possibility for the potential of PAF materials in anionic conductive membranes.

Crystalline nanosheets of three-dimensional supramolecular frameworks with uniform thickness and high stability

Fabricating three dimensional (3D) supramolecular frameworks (SMFs) into stable crystalline nanosheets remains a great challenge due to the homogeneous and weak inter-building block interactions along 3D directions. Herein, crystalline nanosheets of a 3D SMF with a uniform thickness of 4.8 ± 0.1 nm immobilized with Pt nanocrystals on the surface (Q[8]/Pt NSs) were fabricated via the solid-liquid reaction between cucurbit[8]uril/H2PtCl6 single crystals and hydrazine hydrate with the help of gas and heat yielded during the reaction process. A series of experiments and theoretical calculations reveal the ultrahigh stability of Q[8]/Pt NSs due to the high density hydrogen bonding interaction among neighboring Q[8] molecules. This in turn endows Q[8]/Pt NSs with excellent photocatalytic and continuous thermocatalytic CO oxidation performance, representing the thus-far reported best Pt nano-material-based catalysts.

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.

Continuous Ultrathin Zwitterionic Covalent Organic Framework Membrane Via Surface-Initiated Polymerization Toward Superior Water Retention

Efficient construction of proton transport channels in proton exchange membranes maintaining conductivity under varied humidity is critical for the development of fuel cells. Covalent organic frameworks (COFs) hold great potential in providing precise and fast ion transport channels. However, the preparation of continuous free-standing COF membranes retaining their inherent structural advantages to realize excellent proton conduction performance is a major challenge. Herein, a zwitterionic COF material bearing positive ammonium ions and negative sulphonic acid ions is developed. Free-standing COF membrane with adjustable thickness is constructed via surface-initiated polymerization of COF monomers. The porosity, continuity, and stability of the membranes are demonstrated via the transmission electron microscopy (TEM), atomic force microscopy (AFM), and scanning electron microscopy (SEM) characterization. The rigidity of the COF structure avoids swelling in aqueous solution, which improves the chemical stability of the proton exchange membranes and improves the performance stability. In the higher humidity range (50-90%), the prepared zwitterionic COF membrane exhibits superior capability in retaining the conductivity compared to COF membrane merely bearing sulphonic acid group. The established strategy shows the potential for the application of zwitterionic COF in the proton exchange membrane fuel cells.

Advancing Ion Selective Membranes with Micropore Ion Channels in the Interaction Confinement Regime

Ion exchange membranes allowing the passage of charge-carrying ions have established their critical role in water, environmental, and energy-relevant applications. The design strategies for high-performance ion exchange membranes have evolved beyond creating microphase-separated membrane morphologies, which include advanced ion exchange membranes to ion-selective membranes. The properties and functions of ion-selective membranes have been repeatedly updated by the emergence of materials with subnanometer-sized pores and the understanding of ion movement under confined micropore ion channels. These research progresses have motivated researchers to consider even greater aims in the field, i.e., replicating the functions of ion channels in living cells with exotic materials or at least targeting fast and ion-specific transmembrane conduction. To help realize such goals, we briefly outline and comment on the fundamentals of rationally designing membrane pore channels for ultrafast and specific ion conduction, pore architecture/chemistry, and membrane materials. Challenges are discussed, and perspectives and outlooks are given.

Construction of metal-organic framework/cellulose nanofibers-based hybrid membranes and their ion transport property for efficient osmotic energy conversion

The development of advanced nanofluidic membranes with better ion selectivity, efficient energy conversion and high output power density remains challenging. Herein, we prepared nanofluidic hybrid membranes based on TEMPO oxidized cellulose nanofibers (T-CNF) and manganese-based metal organic framework (MOF) using a simple in situ synthesis method. Incorporated T-CNF endows the MOF/T-CNF hybrid membrane with a high cation selectivity up to 0.93. Nanoporous MOF in three-dimensional interconnected nanochannels provides massive ion transport pathways. High transmembrane ion flux and low ion permeation energy barrier are correlated with a superior energy conversion efficiency (36 %) in MOF/T-CNF hybrid membrane. When operating under 50-fold salinity gradient by mixing simulated seawater and river water, the MOF/T-CNF hybrid membrane achieves a maximum power density value of 1.87 W m-2. About 5-fold increase in output power density was achieved compared to pure T-CNF membrane. The integration of natural nanofibers with high charge density and nanoporous MOF materials is demonstrated an effective and novel strategy for the enhancement of output power density of nanofluidic membranes, showing the great potential of MOF/T-CNF hybrid membranes as efficient nanofluidic osmotic energy generators.