Solvent‐Induced Rearrangement of Ion‐Transport Channels: A Way to Create Advanced Porous Membranes for Vanadium Flow Batteries

Porous membranes with critically hydrophobic/hydrophilic phase‐separated‐like structures for use in vanadium flow battery application are first realized by solvent‐induced reassembly of a polymer blend system. Porous poly(ether sulfone) (PES)/sufonated poly(ether ether ketone) (SPEEK) blend membranes with tunable pore size are prepared via the phase inversion method. After solidification, isopropanol (IPA) is introduced to induce the reassembly of sulfonated groups and further form ion‐transport channels by using the interaction between IPA and functional groups in SPEEK. As a result, a highly phase separated membrane structure is created, composed of a highly stable hydrophobic porous PES matrix and hydrophilic interconnected small pores. The charged pore walls are highly beneficial to improving proton conductivity, while pores are simultaneously shrunk during the IPA treatment. Therefore, the resultant membranes show an excellent battery performance with a coulombic efficiency exceeding 99%, along with an energy efficiency over 91%, which is among the highest values ever reported. This article supplies an ease‐to‐operate and efficient method to create membranes with controlled ion‐transport channels.     

Highly Stable Anion Exchange Membranes with Internal Cross‐Linking Networks

Anion exchange membranes (AEMs) with excellent stability and high ion conductivity are fabricated via the formation of internal cross linking networks. The internal crosslinking networks are constructed by reacting 4,4′‐bipyridine with chloromethylated polysulfone. The bipyridine group simultaneously functions as ionic conductor and cross linker in this system. The performance of the membrane is tuned via controlling the 4,4′‐bipyridine content in the casting solution. The prepared membranes demonstrate excellent chemical stability and high ion conductivity under acidic conditions. As a consequence, the membranes show very promising performance for vanadium flow battery application, exhibiting a Coulombic efficiency of 99.2% and an energy efficiency of 81.8% at a current density of 140 mA cm^?2. The battery that is assembled with the prepared membrane shows a stable battery performance over more than 1600 cycles, which is by far the longest cycle life reported. These results indicate that the AEMs with internal crosslinking structures are promising candidates for battery systems and even for fuel cells.     

Extreme pH-Resistant,Highly Cation-Selective Poly(Quaternary Ammonium) Membranes Fabricated via Menshutkin Reaction-Based Interfacial Polymerization

Membrane-based separation technologies have attracted significant interest from various industries owing to their high process efficiency. However, the wider applications of conventional polyamide (PA) thin-film composite (TFC) membranes are limited by their poor pH stability and low cation selectivity, necessitating the development of membranes with advanced chemistries. Herein, an extreme pH-resistant, highly cation-selective TFC membrane is fabricated by synthesizing a crosslinked poly(quaternary ammonium) (PQA) selective layer on a polyethylene support via Menshutkin reaction-based interfacial polymerization (Men-IP). The Men-IP process produces a thin, densely crosslinked, and positively charged PQA permselective layer without hydrolysis-prone functional groups. The fabricated PQA membrane features a highly selective molecular density that significantly exceeds those of previously reported membranes with non-PA chemistries. Moreover, the PQA membrane exhibits remarkably high rejection (>90%) and selectivity for divalent cations owing to the exceptionally strong positive charge imparted by its abundant cationic QA groups. More importantly, the PQA membrane displays ultrahigh pH stability under both extremely acidic (1.5 m H₂SO₄) and alkaline (5 m NaOH) conditions for 28 days. No other membrane reported in the literature demonstrates such excellent pH stability. This strategy opens a new route for fabricating highly selective membranes that can be used in harsh pH environments.     

Sub-2-nm Channels within Covalent Triazine Framework Enable Fast Proton-Selective Transport in Flow Battery Membrane

Ion conductive membranes (ICMs) with robust sub-2-nm channels show high proton transport rate in flow battery, but it remains a great challenge to precisely control the ion sieving of the membranes. Herein, as a promising proton-selective carrier, sulfonated piperazine covalent triazine framework (s-pCTF) with the channel size of ≈1.5 nm and abundant fast proton hopping sites is introduced into sulfonated poly(ether ether ketone) (SPEEK) to fabricate advanced ICM for vanadium flow battery (VFB) application. The interior protoplasmic channels of s-pCTF demonstrate significant Donnan exclusion effect, resulting in a high proton/vanadium ion selectivity in theory (6.22 × 10⁵). Meanwhile, the nitrogen-rich sub-2-nm channels yield fast proton highway, and exterior-grafted sulfonic acid groups further facilitate the proton transfer. By regulating the ion sieving and proton conductivity, the optimal hybrid membrane exhibits synchronously improved battery performance with an enhanced energy efficiency (92.41% to 78.53% at 40–200 mA cm⁻²) and long-term stability for 900 cycles over 400 h (EE: 87.2–85% at 120 mA cm⁻²), outperforming pure SPEEK and Nafion212 membranes. This study validates the applicability of organic porous CTF with sub-2-nm channels and desired functionality in ICMs for high-performance VFB application.     

Ultra‐Thin Self‐Assembled Protein‐Polymer Membranes: A New Pore Forming Strategy

Self‐assembled membranes offer a promising alternative for conventional membrane fabrication, especially in the field of ultrafiltration. Here, a new pore‐making strategy is introduced involving stimuli responsive protein‐polymer conjugates self‐assembled across a large surface area using drying‐mediated interfacial self‐assembly. The membrane is flexible and assembled on porous supports. The protein used is the cage protein ferritin and resides within the polymer matrix. Upon denaturation of ferritin, a pore is formed which intrinsically is determined by the size of the protein and how it resides in the matrix. Due to the self‐assembly at interfaces, the membrane constitutes of only one layer resulting in a membrane thickness of 7 nm on average in the dry state. The membrane is stable up to at least 50 mbar transmembrane pressure, operating at a flux of about 21 000–25 000 L m^?2 h^?1 bar^?1 and displayed a preferred size selectivity of particles below 20 nm. This approach diversifies membrane technology generating a platform for “smart” self‐assembled membranes.     

A pH‐Responsive Gating Membrane System with Pumping Effects for Improved Controlled Release

In this study, we report on a novel composite membrane system for pH‐responsive controlled release, which is composed of a porous membrane with linear grafted, positively pH‐responsive polymeric gates acting as functional valves, and a crosslinked, negatively pH‐responsive hydrogel inside the reservoir working as a functional pumping element. The proposed system features a large responsive release rate that goes effectively beyond the limit of concentration‐driven diffusion due to the pumping effects of the negatively pH‐responsive hydrogel inside the reservoir. The pH‐responsive gating membranes were prepared by grafting poly(methacrylic acid) (PMAA) linear chains onto porous polyvinylidene fluoride (PVDF) membrane substrates using a plasma‐graft pore‐filling polymerization, and the crosslinked poly(N,N‐dimethylaminoethyl methacrylate) (PDM) hydrogels were synthesized by free radical polymerization. The volume phase‐transition characteristics of PMAA and PDM were opposite. The proposed system opens new doors for pH‐responsive “smart” or “intelligent” controlled‐release systems, which are highly attractive for drug‐delivery systems, chemical carriers, sensors, and so on.     

All‐Carbon Nanoarchitectures as High‐Performance Separation Membranes with Superior Stability

The application of graphene‐based membranes is hindered by their poor stability under practical hydrodynamic conditions. Here, nanocarbon architectures are designed by intercalating surface‐functionalized, small‐diameter, multi‐walled carbon nanotubes (MWCNTs) into reduced graphene oxide (rGO) sheets to create highly stable membranes with improved water permeability and enhanced membrane selectivity. With the intercalation of 10 nm diameter MWCNTs, the water permeability reaches 52.7 L m^?2 h^?1 bar^?1, which is 4.8 times that of pristine rGO membrane and five to ten times higher than most commercial nanofiltration membranes. The membrane also attains almost 100% rejection for three organic dyes of different charges. More importantly, the membrane can endure a turbulent hydrodynamic flow with cross‐flow rates up to 2000 mL min^?1 and a Reynolds number of 4667. Physicochemical characterization reveals that the inner graphitic walls of the MWCNTs can serve as spacers, while nanoscale rGO foliates on the outer walls interconnect with the assimilated rGO sheets to instill superior membrane stability. In contrast, intercalating with single‐walled nanotubes fails to reproduce such stability. Overall, this nanoarchitectured design is highly versatile in creating both graphene‐rich and CNT‐rich all‐carbon membranes with engineered nanochannels, and is regarded as a general approach in obtaining stable membranes for realizing practical applications of graphene‐based membranes.     

Oxidation‐Resistant and Elastic Mesoporous Carbon with Single‐Layer Graphene Walls

An oxidation‐resistant and elastic mesoporous carbon, graphene mesosponge (GMS), is prepared. GMS has a sponge‐like mesoporous framework (mean pore size is 5.8 nm) consisting mostly of single‐layer graphene walls, which realizes a high electric conductivity and a large surface area (1940 m² g^?1). Moreover, the graphene‐based framework includes only a very small amount of edge sites, thereby achieving much higher stability against oxidation than conventional porous carbons such as carbon blacks and activated carbons. Thus, GMS can simultaneously possess seemingly incompatible properties; the advantages of graphitized carbon materials (high conductivity and high oxidation resistance) and porous carbons (large surface area). These unique features allow GMS to exhibit a sufficient capacitance (125 F g^?1), wide potential window (4 V), and good rate capability as an electrode material for electric double‐layer capacitors utilizing an organic electrolyte. Hence, GMS achieves a high energy density of 59.3 Wh kg^?1 (material mass base), which is more than twice that of commercial materials. Moreover, the continuous graphene framework makes GMS mechanically tough and extremely elastic, and its mean pore size (5.8 nm) can be reversibly compressed down to 0.7 nm by simply applying mechanical force. The sponge‐like elastic property enables an advanced force‐induced adsorption control.     

A Cost‐Effective Mixed Matrix Polyethylene Porous Membrane for Long‐Cycle High Power Density Alkaline Zinc‐Based Flow Batteries

Alkaline zinc‐based flow batteries (ZFBs) have received considerable interest for renewable energy storage due to their attractive features of low cost and high energy density. However, a membrane with high stability, high selectivity, and high ion conductivity is in urgent need. Herein, an economical mixed matrix membrane with highly anti‐alkali microporous hollow spheres (denoted as DM‐HM) is developed in this work. With excellent chemical and mechanical stability, DM‐HM can achieve a high area capacity of 100 mA h cm^?2 for carbon felt (CF)||Zn@CF symmetrical flow battery, and thereby exhibits 500 stable cycles with a coulombic efficiency of 98.6% and an energy efficiency of 88.3% at 80 mA cm^?2 for alkaline zinc–iron flow battery. Additionally, with 44 wt% of hollow spheres inside matrix, DM‐HM can dramatically shorten the ion transport pathway and results in a very high power density battery. A kilowatt stack assembled with DM‐HM shows a very impressive performance, further confirming the practicability of this scalable mixed matrix membrane for alkaline ZFBs.     

On the Origin of Ion Selectivity in Ultrathin Nanopores: Insights for Membrane‐Scale Osmotic Energy Conversion

Nanopores in ultrathin or atomically thin membranes attract broad interest because the infinitesimal pore depth allows selective transport of ions and molecules with ultimate permeability. Toward large‐scale osmotic energy conversion, great challenges remain in extrapolating the promising single‐pore demonstration to really powerful macroscopic applications. Herein, the origin of the selective ion transport in ultrathin nanopores is systematically investigated. Based on a precise Poisson and Nernst–Planck model calculation, it is found that the generation of net diffusion current and membrane potential stems from the charge separation within the electric double layer on the outer membrane surface, rather than that on the inner pore wall. To keep the charge selectivity of the entire membrane, a critical surface charged area surrounding each pore orifice is therefore highly demanded. Otherwise, at high pore density, the membrane selectivity and the overall power density would fall down instead, which explains the giant gap between the actual experimental achievements and the single‐pore estimation. To maximize the power generation, smaller nanopores (pore diameter ≈1–2 nm) are appropriate for large‐scale osmotic energy conversion. With a porosity of ≈10%, the total power density approaches more than 200 W m^‐2, anticipating a substantial advance toward high‐performance large‐scale nanofluidic power sources.     

Proton Transport from Dendritic Helical‐Pore‐Incorporated Polymersomes

The ability to add synthetic channels to polymersome (polymer vesicle) membranes could lead to novel membrane composites with unique selectivity and permeability. Proton transport through two different synthetic pores, self‐assembled from either a dendritic dipeptide, (6Nf‐3,4‐3,5)12G2‐CH₂‐Boc‐L‐Tyr‐L‐Ala‐OMe, or a dendritic ester, (R)‐4Bp‐3,4‐dm8G1‐COOMe, incorporated into polymersome membranes are studied. Polymersomes provide an excellent platform for studying such transport processes due to their robustness and mechanical and chemical stability compared to liposomes. It is found that the incorporated dendritic dipeptide and dendritic ester assemble into stable helical pores in the poly(ethylene oxide)‐polybutadiene (PEO‐PBD) polymersomes but not in the poly(2‐methyloxazoline)‐poly(dimethylsiloxane)‐poly(2‐methyl oxazoline) (PMOX‐PDMS‐PMOX) polymersomes. The incorporation is confirmed by circular dichroism (CD), changes in purely synthetic mechanical strength (e.g., areal expansion modulus) as assessed by micropipette aspiration, and cryo‐TEM. In addition to the structural analyses, a transport measurement shows the incorporated dendritic helical pores allow facile transport of protons across the polymersome membranes after up to one month of storage. This integration of synthetic porous channels with polymersome substrates could provide a valuable tool for studying active transport processes in a composite membrane. These composites will ultimately expand the family of biologically inspired porous‐membrane mimics.     

pH‐Responsive Nanoporous Silica Colloidal Membranes

Free‐standing colloidal membranes (nanofrits) with varied thickness and nanopore size are fabricated and modified with pH‐responsive poly(2‐(dimethylamino)ethyl methacrylate) brushes. The polymer‐modified nanofrits demonstrate excellent gating behavior for molecular diffusion: in the presence of acid, the diffusion rate of positively charged species significantly decreases. Increasing the polymer length and membrane thickness and decreasing the nanopore size leads to the complete acid‐controlled gating of the membranes.     

Stomata‐Inspired Membrane Produced Through Photopolymerization Patterning

The programmed movements of responsive functional hydrogels have received much attention because of their abundant functions and wide range of engineering applications. In this study, an innovative stomata‐inspired membrane (SIM) is fabricated by using a temperature‐responsive hydrogel through a simple, cost‐effective, and high‐throughput patterned photopolymerization. Polymerization‐induced diffusion on the macroscale surface results in formation of a double‐parted polymer membrane with fine pores after single illumination. After heating the SIM, the less deformable thick frame supports the whole structure and the highly deformable thin base regulates pore shape. Among various SIM types, the slit pores of monocot SIM, which are lined up in parallel, exhibit the largest radius deformation. The morphological configuration of the SIM can be easily controlled by changing the photomask for a given application. As the developed SIM features the sensing‐to‐activation functions of stimuli‐responsive hydrogels and can be easily fabricated, this membrane can be potentially used for numerous practical applications, such as filter membranes with adjustable pores, membrane‐based sensors, membrane‐based actuators, and multifunctional membranes.     

Functional and Well‐Defined β‐Sheet‐Assembled Porous Spherical Shells by Surface‐Guided Peptide Formation

Polypeptides have attracted widespread attention as building blocks for complex materials due to their ability to form higher‐ordered structures such as β‐sheets. However, the ability to precisely control the formation of well‐defined β‐sheet‐assembled materials remains challenging as β‐sheet formation tends to lead to ill‐defined and unprocessable aggregates. This work reports a simple, rapid, and robust strategy to form well‐defined peptide β‐sheet‐assembled shells (i.e., hollow spheres) by employing surface‐initiated N‐carboxyanhydride ring‐opening polymerization under a highly efficient surface‐driven approach. The concept is demonstrated by the preparation of enzyme‐degradable rigid shell architectures composed of H‐bonded poly(L‐valine) (PVal) grafts with porous and sponge‐like surface morphology. The porous PVal‐shells exhibit a remarkable and unprecedented ability to non‐covalently entrap metal nanoparticles, proteins, drug molecules, and biorelevant polymers, which could potentially lead to a diverse range of biodegradable and functional platforms for applications ranging from therapeutic delivery to organic catalysis.     

A Thermoresponsive Membrane for Chiral Resolution

A novel thermoresponsive membrane for chiral resolution with high performance has been developed. The membrane exhibits chiral selectivity based on molecular recognition of beta‐cyclodextrin (β‐CD) and thermosensitivity based on the phase transition of poly(N‐isopropylacrylamide) (PNIPAM). Linear PNIPAM chains were grafted onto porous nylon‐6 membrane substrates by using a plasma‐graft pore‐filling polymerization method; the chains thus acted as microenvironmental adjustors for β‐CD molecules. β‐CD moieties were introduced into the linear PNIPAM chains by a chemical grafting polymerization method and acted as chiral selectors. The phase transition of grafted PNIPAM chains affects the microenvironment of β‐CD molecules and, thus, the association between β‐CD and guest molecules. The chiral selectivity of the prepared thermoresponsive membranes in chiral resolution operated at temperature below the lower critical solution temperature (LCST) of PNIPAM is higher than that of membranes with no thermosensitivity. Furthermore, the decomplexation ratio of enantiomer‐loaded thermoresponsive membranes in decomplexation at temperatures above the LCST is much higher than that of membranes with no thermosensitivity. Thus, by simply changing the operation temperature, high, selective chiral resolution and efficient membrane regeneration are achieved. The proposed membrane provides a new and efficient way to solve the difficult decomplexation problem of chiral solid membranes, which is highly attractive for chiral resolution.     

High‐Yield Fabrication,Activation, and Characterization of Carbon Nanotube Ion Channels by Repeated Voltage‐Ramping of Membrane‐Capillary Assembly

The interior channels of carbon nanotubes are promising for studying transport of individual molecules in a 1D confined space. However, experimental investigations of the interior transport have been limited by the extremely low yields of fabricated nanochannels and their characterization. Here, this challenge is addressed by assembling nanotube membranes on glass capillaries and employing a voltage‐ramping protocol. Centimeter‐long carbon nanotubes embedded in an epoxy matrix are sliced to hundreds of 10 µm‐thick membranes containing essentially identical nanotubes. The membrane is attached to glass capillaries and dipped into analyte solution. Repeated ramping of the transmembrane voltage gradually increases ion conductance and activates the nanotube ion channels in 90% of the membranes; 33% of the activated membranes exhibit stochastic pore‐blocking events caused by cation translocation through the interiors of the nanotubes. Since the membrane‐capillary assembly can be handled independently of the analyte solution, fluidic exchange can be carried out simply by dipping the capillary into a solution of another analyte. This capability is demonstrated by sequentially measuring the threshold transmembrane voltages and ion mobilities for K⁺, Na⁺, and Li⁺. This approach, validated with carbon nanotubes, will save significant time and effort when preparing and testing a broad range of solid‐state nanopores.     

Sponge‐Templated Preparation of High Surface Area Graphene with Ultrahigh Capacitive Deionization Performance

Capacitive deionization (CDI) is a competent water desalination technique offering an appropriate route to obtain clean water. However, a rational designed structure of the electrode materials is essentially required for achieving high CDI performance. Here, a novel sponge‐templated strategy is developed for the first time to prepare graphene sheets with high specific surface area and suitable pore size distribution. Sponge is used as the support of graphene oxide to prevent the restack of graphene sheets, as well as to suppress the agglomerate during the annealing process. Importantly, the as‐fabricated graphene sheets possess high specific surface area of 305 m² g^?1 and wide pore size distribution. Ultrahigh CDI performance, a remarkable electrosorptive capacity of 4.95 mg g^?1, and siginificant desorption rate of 25 min, is achieved with the sponge‐templated prepared graphene electrodes. This work provides an effective solution for the synthesis of rational graphene architectures for general applications in CDI, energy storage and conversion.     

Engineering Carbon Nanotube Forest Superstructure for Robust Thermal Desalination Membranes

Desalination by membrane distillation (MD) using low‐grade or waste heat provides a potential route for sustainable water supply. Nonwetting, porous membranes that provide a selective pathway for water vapor over nonvolatile salt are at the core of MD desalination. Conventional water‐repelling MD membranes (i.e., hydrophobic and superhydrophobic membranes) fail to ensure long‐term desalination performance due to pore wetting and surface fouling. To address these challenges, a defect‐free carbon nanotube forest (CNTF) is engineered in situ on a porous electrospun silica fiber substrate. The engineered CNTF forms an ultrarough and porous interface structure, allowing outstanding wetting resistance against water in air and oil underwater. As a result of this antiwetting property, the composite CNTF membrane displays a stable water vapor flux and a near complete salt rejection (>99.9%) in the desalination of highly saline water containing low surface tension contaminants. The antimicrobial property of the composite CNTF membrane imparted by the unique forest‐like architecture and the oxidative effect of carbon nanotubes (CNTs) are further demonstrated. The results exemplify an effective strategy for engineering CNT architecture to elucidate the structure–property–performance relationship of the nanocomposite membranes and to guide the design of robust thermal desalination membranes.     

Understanding the Ion Transport Behavior across Nanofluidic Membranes in Response to the Charge Variations

Biological pores regulate the cellular traffic of a diverse collection of molecules, often with extremely high selectivity. Given the ubiquity of charge-based separation in nature, understanding the link between the charged functionalities and the ion transport activities is essential for designing delicate separations, with the correlation being comparatively underdeveloped. Herein, the effect of charge density from the impact of pore structure is decoupled using a multivariate strategy for the construction of covalent organic framework-based membranes. How the density of charged sites in the nanofluidic membranes affect the ion transport activity with particular emphasis on Li⁺ and Mg²⁺ ions, relevant to the challenge of salt-lake lithium mining is systematically investigated. Systematic control of the charge distribution produces membranes with numerous advantages, overcoming the long-term challenge of Li⁺/Mg²⁺ separation. The top membrane exhibits an outstanding equilibrium selectivity for Li⁺ over Mg²⁺ and operational stability under diffusion dialysis and electrodialysis conditions (Li⁺/Mg²⁺ up to 500), qualifying it as a potential candidate for lithium extraction. It is anticipated that the developed nanofluidic membrane platform can be further leveraged to tackle other challenges in controlled separation processes.     

Biomass Valorization via Paired Electrosynthesis Over Vanadium Nitride‐Based Electrocatalysts

Paired electrosynthesis is a promising technology with the potential to generate value‐added products at both electrodes in a cost‐effective manner. Herein, 3D vanadium nitride (VN) and Pd/VN hollow nanospheres are successfully fabricated and coupled to carry out simultaneous electrocatalytic oxidation (ECO) and electrocatalytic hydrogenation (ECH) of 5‐hydroxymethylfurfural (HMF) into 2, 5‐furandicarboxylic acid (FDCA) and 2,5‐bishydroxymethyl‐tetrahydrofuran (DHMTHF), respectively. VN shows excellent ECO performance with high HMF conversion (≥98%), FDCA selectivity (≥96%), and faradaic efficiency (≥84%) after a stability test, and Pd/VN achieves high ECH selectivity for DHMTHF at ≥88% and an HMF conversion of ≥90%, with a faradaic efficiency of ≥86%. VN and Pd/VN incorporated into a membrane electrode assembly in a paired electrolysis system shows potential for large‐scale biomass conversion and upgrading. Theoretical calculations reveal that the higher performance of VN for the production of ECO can be attributed to its lower d‐band center level relative to the Fermi level compared to that of V₂O₅, which favors HMF chemisorption and activation. This study paves the way for developing paired electrosynthesis technologies with the potential for biomass utilization and energy conversion.