Bioinspired Ultrastrong Solid Electrolytes with Fast Proton Conduction along 2D Channels

2D Biomimetic Membranes Constructed by Charge Assembly and Hydrogen Bonding for Precise Ion Separation

Designing well-ordered, multifunctional layered membranes with high selectivity and long-term stability remains a significant challenge. Here, a simple strategy is introduced that utilizes charge repulsion between graphene oxide (GO) and engineered bacteria to induce liquid crystal formation, enabling their layer-by-layer self-assembly on a polyethersulfone membrane. The interlayer pressure flattens the bacteria, removing interlayer water and forming a densely packed structure. This compression decreases the spacing between functional groups, leading to a robust hydrogen bonding network and a significant enhancement in mechanical properties (12.42 times tensile strength increase). Notably, the pressure preserves the activity of the super uranyl-binding protein of engineered bacteria, which selectively coordinates with uranyl (UO2 2+) through high-affinity coordination bonds, enabling recognition and sieving of target ions. The membrane demonstrates near 100% rejection of UO2 2+, K/U, and V/U selectivity of ≈140 and ≈40, respectively, while maintaining long-term stability. This strategy provides a versatile platform for the precise design of high-performance membranes, advancing the field of molecular transport in energy and environmental applications.

Modulating Electrochemical Energy Storage and Multi-Spectra Defense of MXenes by Interfacial Dual-Filler Engineering

MXenes have attracted growing interest in electrochemical energy storage owing to their high electronic conductivity and editable surface chemistry. Besides, rendering MXenes with spectrum defense properties further broadens their versatile applications. However, the development of MXenes suffers from weak van der Waal interaction-driven self-restacking that leads to random alignment and inferior interface microenvironments. Herein, a nacre-inspired MXene film is tailored by dual-filling of 2-ureido-4[1H]-pyrimidinone (UPy)-modified polyvinyl alcohol (PVA-UPy) and carbon nanotubes (CNTs). The dual-nanofillers engineering endows the nanocomposite film with a highly ordered structure (a Herman's order value of 0.838), a high mechanical strength (139.5 MPa), and continuous conductive pathways of both the ab plane and c-axis. As a proof-of-concept, the tailored nanocomposite film achieves a considerable capacitance of 508.2 F cm-3 and long-term cycling stability without performance degradation for 10 000 cycles. It is efficient for spectra defense in radar and infrared bands, displaying a high electromagnetic shielding capacity (19186 dB cm2 g-1) and a super-low infrared (IR) emissivity (0.16), with negligible performance decay after saving in the air for 1 year, responsible for the applications in specific and complex conditions. This interfacial dual-filler engineering concept showcases effective nanotechnology toward sustainable energy applications with a long lifetime and safety.

Diethylenetriaminepentaacetic Acid-based Conducting Solid Polymer Electrolytes Impede Lithium Dendrites and Impart Antioxidant Capacity in Lithium-Ion Batteries

In the development of lithium-ion batteries (LIBs), cheaper and safer solid polymer electrolytes are expected to replace combustible organic liquid electrolytes to meet the larger market demand. However, low ionic conductivity and inadequate cycling stability impede their commercial viability. Herein, a novel flexible conducting solid polymer electrolytes (CSPEs) based on polyvinyl alcohol (PVA) and ion-polarized diethylenetriaminepentaacetic acid (P-DETP) is developed for the first time and applied in LIBs. PVA and P-DETP form a compact polymer network through hydrogen bonding, enhancing the thermomechanical stability of CSPE while restricting the migration of larger anions. Furthermore, density functional theory calculations confirm that P-DETP can facilitate the dissociation of Li+-TFSI- via electrostatic attraction, resulting in increased mobility of lithium ions. Additionally, P-DETP contributes to the formation of a stable electrode-electrolyte interface layer, effectively suppressing the growth of lithium dendrites and improving antioxidant capacity. These synergistic effects enable CSPE to exhibit remarkable properties including high ionic conductivity (2.8 × 10-4 S cm-1), elevated electrochemical potential (5.1 V), and excellent lithium transference number (0.869). Notably, the P-DETP/LiTFSI CSPE demonstrates stable performance not only in LiFePO4 batteries but also adapts to high-nickel ternary LiNi0.88Co0.06Mn0.06O2 cathode, highlighting its immense potential for application in high energy density LIBs.

Review: Application of Bionic-Structured Materials in Solid-State Electrolytes for High-Performance Lithium Metal Batteries

Solid-state lithium metal batteries (SSLMBs) have gained significant attention in energy storage research due to their high energy density and significantly improved safety. But there are still certain problems with lithium dendrite growth, interface stability, and room-temperature practicality. Nature continually inspires human development and intricate design strategies to achieve optimal structural applications. Innovative solid-state electrolytes (SSEs), inspired by diverse natural species, have demonstrated exceptional physical, chemical, and mechanical properties. This review provides an overview of typical bionic-structured materials in SSEs, particularly those mimicking plant and animal structures, with a focus on their latest advancements in applications of solid-state lithium metal batteries. Commencing from plant structures encompassing roots, trunks, leaves, flowers, fruits, and cellular levels, the detailed influence of biomimetic strategies on SSE design and electrochemical performance are presented in this review. Subsequently, the recent progress of animal-inspired nanostructures in SSEs is summarized, including layered structures, surface morphologies, and interface compatibility in both two-dimensional (2D) and three-dimensional (3D) aspects. Finally, we also evaluate the current challenges and provide a concise outlook on future research directions. We anticipate that the review will provide useful information for future reference regarding the design of bionic-structured materials in SSEs.

Building intercalation structure for high ionic conductivity via aliovalent substitution

Two-dimensional (2D) materials, which possess robust nanochannels, high flux and allow scalable fabrication, provide new platforms for nanofluids. Highly efficient ionic conductivity can facilitate the application of nanofluidic devices for modern energy conversion and ionic sieving. Herein, we propose a novel strategy of building an intercalation crystal structure with negative surface charge and mobile interlamellar ions via aliovalent substitution to boost ionic conductivity. The Li2xM1-xPS3 (M = Cd, Ni, Fe) crystals obtained by the solid-state reaction exhibit distinct capability of water absorption and apparant variation of interlayer spacing (from 0.67 to 1.20 nm). The assembled membranes show the ultrahigh ionic conductivity of 1.20 S/cm for Li0.5Cd0.75PS3 and 1.01 S/cm for Li0.6Ni0.7PS3. This facile strategy may inspire the research in other 2D materials with higher ionic transport performance for nanofluids.

Confined Ionic-Liquid-Mediated Cation Diffusion through Layered Membranes for High-Performance Osmotic Energy Conversion

Ion-selective membranes act as the core components in osmotic energy harvesting, but remain with deficiencies such as low ion selectivity and a tendency to swell. 2D nanofluidic membranes as competitive candidates are still subjected to limited mass transport brought by insufficient wetting and poor stability in water. Here, an ionic-liquid-infused graphene oxide (GO@IL) membrane with ultrafast ion transport ability is reported, and how the confined ionic liquid mediates selective cation diffusion is revealed. The infusion of ionic liquids endows the 2D membrane with excellent mechanical strength, anti-swelling properties, and good stability in aqueous electrolytes. Importantly, immiscible ionic liquids also provide a medium, allowing partial dehydration for ultrafast ion transport. Through molecular dynamics simulation and finite element modeling, that GO nanosheets induce ionic liquids to rearrange, bringing in additional space charges, which can be coupled with GO synergistically, is proved. By mixing 0.5/0.01 m NaCl solution, the power density can achieve a record value of ≈6.7 W m^-2 , outperforming state-of-art GO-based membranes. This work opens up a new route for boosting nanofluidic energy conversion because of the diversity of the ILs and 2D materials.

Highly Elastic, Healable, and Durable Anhydrous High-Temperature Proton Exchange Membranes Cross-Linked with Highly Dense Hydrogen Bonds

Proton exchange membranes (PEMs) with excellent durability and working stability are important for PEM fuel cells with extended service life and enhanced reliability. In this study, highly elastic, healable, and durable electrolyte membranes are fabricated by the complexation of poly(urea-urethane), ionic liquids (ILs), and MXene nanosheets (denoted as PU-IL-MX). The resulting PU-IL-MX electrolyte membranes have a tensile strength of ≈3.86 MPa and a strain at break of ≈281.89%. The PU-IL-MX electrolyte membranes can act as high temperature PEMs to conduct protons under an anhydrous condition of the temperatures above 100 °C. Importantly, the ultrahigh density of hydrogen-bond-cross-linked network renders PU-IL-MX membranes excellent IL retention properties. The membranes can maintain more than ≈98% of their original weight and show no decline of proton conductivity after being placed under highly humid conditions of ≈80 °C and relative humidity of ≈85% for 10 days. Moreover, due to the reversibility of hydrogen bonds, the membranes can heal damage under the working conditions of fuel cells to restore their original mechanical properties, proton conductivities, and cell performances.

Nitrogen Dense Distributions of Imidazole Grafted Dipyridyl Polybenzimidazole for a High Temperature Proton Exchange Membrane

The introduction of basic groups in the polybenzimidazole (PBI) main chain or side chain with low phosphoric acid doping is an effective way to avoid the trade-off between proton conductivity and mechanical strength for high temperature proton exchange membrane (HT-PEM). In this study, the ethyl imidazole is grafted on the side chain of the PBI containing bipyridine in the main chain and blended with poly(2,2′-[p-oxydiphenylene]-5,5′-benzimidazole) (OPBI) to obtain a series of PBI composite membranes for HT-PEMs. The effects of the introduction of bipyridine in the main chain and the ethyl imidazole in the side chain on proton transport are investigated. The result suggests that the introduction of the imidazole and bipyridine group can effectively improve the comprehensive properties as HT-PEM. The highest of proton conductivity of the obtained membranes under saturated phosphoric acid (PA) doping can be up to 0.105 S cm⁻¹ at 160 °C and the maximum output power density is 836 mW cm⁻² at 160 °C, which is 2.3 times that of the OPBI membrane. Importantly, even at low acid doping content (~178%), the tensile strength of the membrane is 22.2 MPa, which is nearly 2 times that of the OPBI membrane, the proton conductivity of the membrane achieves 0.054 S cm⁻¹ at 160 °C, which is 2.3 times that of the OPBI membrane, and the maximum output power density of a single cell is 540 mW cm⁻² at 160 °C, which is 1.5 times that of the OPBI membrane. The results suggest that the introduction of a large number of nitrogen-containing sites in the main chain and side chain is an efficient way to improve the proton conductivity, even at a low PA doping level.

MOF-COF "Alloy" Membranes for Efficient Propylene/Propane Separation

Molecular-sieving membranes from metal-organic frameworks (MOFs) are promising candidates for separating olefin/paraffin mixtures, a critical demand in sustainable chemical processes and a grand challenge in molecular separation. Currently, the inherent lattice flexibility of MOFs severely compromises their precise sieving ability. Here, a proof-of-concept of "alloy" membranes (AMs), which are fabricated by incorporating quaternary ammonium (QA)-functionalized covalent organic frameworks (COFs) into a zeolitic imidazolate framework-8 (ZIF-8) matrix is demonstrated. The Coulomb force between the COFs and the ZIF-8 restricts the linker rotation of the ZIF-8, generating a distinct alloying effect, by which the lattice rigidity of ZIF-8 can be conveniently tuned through varying the content of the COFs, similar to the flexible-to-rigid transition in aluminum alloy manufacturing. Such an alloying effect confers the AM's superior propylene/propane separation performance, with a propylene/propane separation factor surpassing 200 and a propylene permeance of 168 GPU. Hopefully, the AMs concept and the concomitant alloying effect can update the connotation of mixed matrix membranes and stimulate the re-envisioning about the design paradigm and development of advanced membranes for energy-efficient separations.

Biomimic Heterostructured Graphene Oxide Membranes via Supramolecular-Mediated Intercalation Assembly for Efficient Water Transport

Two-dimensional (2D) lamellar membranes have attracted increasing attention for efficient water purification. However, the low water-permeability, structural failure in aqua and high production cost have significantly restricted their practical large-scale applications. Inspired by the structures of glomerular filtration barrier (GFB) and nacre, a high-performance biomimic membrane via supramolecular-mediated intercalation assembly is reported, where rod-shaped cyclodextrin (CD) functionalized attapulgite (ATP-CD) is intercalated into CD-modified graphene oxide (GO-CD) lamellar channels, followed by locking adjacent ATP-CD and GO-CD through tannic acid (TA) and CD supramolecular networks. The formed GFB-like heterostructure endows the membrane with excellent water transport capability and the bionic "brick and mortar" nacre configuration boosts its anti-swelling stability simultaneously. The heterostructured GO membranes (≈100 nm) fabricated in this way exhibit a good water permeability of 55.6 L m^-2  h^-1  bar^-1 (≈20-fold higher than GO membrane) maintaining excellent dye rejection of >99% during 480 h immersion. Given the low-cost materials (ATP, CD, and TA) and the modification generality, this economic strategy can hopefully achieve large-scale membrane fabrication and afford high applicability, which promotes the practical engineering applications of such 2D material membranes.

Bioinspired Materials for Energy Storage

Nature offers a variety of interesting structures and intriguing functions for researchers to be learnt for advanced materials innovations. Recently, bioinspired materials have received intensive attention in energy storage applications. Inspired by various natural species, many new configurations and components of energy storage devices, such as rechargeable batteries and supercapacitors, have been designed and innovated. The bioinspired designs on energy devices, such as electrodes and electrolytes, have brought about excellent physical, chemical, and mechanical properties compared to the counterparts at their conventional forms. In this review, the design principles for bioinspired materials ranging from structures, synthesis, and functionalization to multi-scale ordering and device integration are first discussed, and then a brief summary is given on the recent progress on bioinspired materials for energy storage systems, particularly the widely studied rechargeable batteries and supercapacitors. Finally, a critical review on the current challenges and brief perspective on the future research focuses are proposed. It is expected that this review can offer some insights into the smart energy storage system design by learning from nature.

Mixed-dimensional membranes: chemistry and structure-property relationships

Tremendous progress in two-dimensional (2D) nanomaterial chemistry affords abundant opportunities for the sustainable development of membranes and membrane processes. In this review, we propose the concept of mixed dimensional membranes (MDMs), which are fabricated through the integration of 2D materials with nanomaterials of different dimensionality and chemistry. Complementing mixed matrix membranes or hybrid membranes, MDMs stimulate different conceptual thinking about designing advanced membranes from the angle of the dimensions of the building blocks as well as the final structures, including the nanochannels and the bulk structures. In this review, we survey MDMs (denoted nD/2D, where n is 0, 1 or 3) in terms of the dimensions of membrane-forming nanomaterials, as well as their fabrication methods. Subsequently, we highlight three kinds of nanochannels, which are 1D nanochannels within 1D/2D membranes, 2D nanochannels within 0D/2D membranes, and 3D nanochannels within 3D/2D membranes. Strategies to tune the physical and chemical microenvironments of the nanochannels as well as the bulk structures based on the size, type, structure and chemical character of nanomaterials are discussed. Some representative applications of MDMs are illustrated for gas molecular separations, liquid molecular separations, ionic separations and oil/water separation. Finally, current challenges and a future perspective on MDMs are presented.

Rational ion transport management mediated through membrane structures

Unique membrane structures endow membranes with controlled ion transport properties in both biological and artificial systems, and they have shown broad application prospects from industrial production to biological interfaces. Herein, current advances in nanochannel-structured membranes for manipulating ion transport are reviewed from the perspective of membrane structures. First, the controllability of ion transport through ion selectivity, ion gating, ion rectification, and ion storage is introduced. Second, nanochannel-structured membranes are highlighted according to the nanochannel dimensions, including single-dimensional nanochannels (i.e., 1D, 2D, and 3D) functioning by the controllable geometrical parameters of 1D nanochannels, the adjustable interlayer spacing of 2D nanochannels, and the interconnected ion diffusion pathways of 3D nanochannels, and mixed-dimensional nanochannels (i.e., 1D/1D, 1D/2D, 1D/3D, 2D/2D, 2D/3D, and 3D/3D) tuned through asymmetric factors (e.g., components, geometric parameters, and interface properties). Then, ultrathin membranes with short ion transport distances and sandwich-like membranes with more delicate nanochannels and combination structures are reviewed, and stimulus-responsive nanochannels are discussed. Construction methods for nanochannel-structured membranes are briefly introduced, and a variety of applications of these membranes are summarized. Finally, future perspectives to developing nanochannel-structured membranes with unique structures (e.g., combinations of external macro/micro/nanostructures and the internal nanochannel arrangement) for mediating ion transport are presented.

In Situ-Doped Superacid in the Covalent Triazine Framework Membrane for Anhydrous Proton Conduction in a Wide Temperature Range from Subzero to Elevated Temperature

Synthesis of solid-state proton-conducting membranes with low activation energy and high proton conductivity under anhydrous conditions is a great challenge. Here, we show a simple and convenient way to prepare covalent triazine framework membranes (CTF-Mx) with acid in situ doping for anhydrous proton conduction in a wide temperature range from subzero to elevated temperature (160 °C). The low proton dissociation energy and continuous hydrogen bond network in CTF-Mx make the membrane achieve high proton conductivity from 1.21×10^-3 S cm^-1 (-40 °C) to 2.08×10^-2 S cm^-1 (160 °C) under anhydrous conditions. Molecular dynamics and proton relaxation time analyses reveal proton hopping at low activation energies with greatly enhanced mobility in the CTF membranes.

Weakly Humidity-Dependent Proton-Conducting COF Membranes

State-of-the-art proton exchange membranes (PEMs) often suffer from significantly reduced conductivity under low relative humidity, hampering their efficient application in fuel cells. Covalent organic frameworks (COFs) with pre-designable and well-defined structures hold promise to cope with the above challenge. However, fabricating defect-free, robust COF membranes proves an extremely difficult task due to the poor processability of COF materials. Herein, a bottom-up approach is developed to synthesize intrinsic proton-conducting COF (IPC-COF) nanosheets (NUS-9) in aqueous solutions via diffusion and solvent co-mediated modulation, enabling a controlled nucleation and in-plane-dominated IPC-COF growth. These nanosheets allow the facile fabrication of IPC-COF membranes. IPC-COF membranes with crystalline, rigid ion nanochannels exhibit a weakly humidity-dependent conductivity over a wide range of humidity (30-98%), 1-2 orders of magnitude higher than that of benchmark PEMs, and a prominent fuel cell performance of 0.93 W cm^-2 at 35% RH and 80 °C arising from superior water retention and Grotthuss mechanism-dominated proton conduction.

Ultratough graphene-black phosphorus films

Graphene-based films with high toughness have many promising applications, especially for flexible energy storage and portable electrical devices. Achieving such high-toughness films, however, remains a challenge. The conventional mechanisms for improving toughness are crack arrest or plastic deformation. Herein we demonstrate black phosphorus (BP) functionalized graphene films with record toughness by combining crack arrest and plastic deformation. The formation of covalent bonding P-O-C between BP and graphene oxide (GO) nanosheets not only reduces the voids of GO film but also improves the alignment degree of GO nanosheets, resulting in high compactness of the GO film. After further chemical reduction and π-π stacking interactions by conjugated molecules, the alignment degree of rGO nanosheets was further improved, and the voids in lamellar graphene film were also further reduced. Then, the compactness of the resultant graphene films and the alignment degree of reduced graphene oxide nanosheets are further improved. The toughness of the graphene film reaches as high as ∼51.8 MJ m^-3, the highest recorded to date. In situ Raman spectra and molecular dynamics simulations reveal that the record toughness is due to synergistic interactions of lubrication of BP nanosheets, P-O-C covalent bonding, and π-π stacking interactions in the resultant graphene films. Our tough black phosphorus functionalized graphene films with high tensile strength and excellent conductivity also exhibit high ambient stability and electromagnetic shielding performance. Furthermore, a supercapacitor based on the tough films demonstrated high performance and remarkable flexibility.

Supramolecular Calix[n]arenes-Intercalated Graphene Oxide Membranes for Efficient Proton Conduction

Graphene oxide (GO) membranes with 2D interlaminar channels have triggered intensive interest as ion conductors. Incorporating abundant ion-conducting sites into GO interlayers is recognized as an effective strategy to facilitate ion conduction. Herein, we designed supramolecular compounds, para-sulphonato-calix[n]arenes (p-SC[n]As), as versatile intercalators to acquire highly conductive and robust GO membranes. The SC[n]A with ultrahigh ionic exchange capacity (IEC_w, 5.37 mmol g^-1) imparts sufficient proton donors, and its rigid framework imparts strong support of adjacent nanosheets. We designed three kinds of SC[n]As with the same IEC_w but different sizes as intercalators, endowing the GO/SC[n]A membranes with increasing ion concentration and d-spacing in the order of GO/SC[4]A < GO/SC[6]A < GO/SC[8]A. Therefore, the interlayers of GO/SC[8]A membranes afforded higher density of proton donors and could accommodate more water molecules to construct more continuous H-bond networks for proton transfer. Accordingly, the proton conductivities exhibited the same increasing trend, up to 327.0 mS cm^-1 of GO/SC[8]A-30% at 80 °C, 100% RH, which was 2.80 times higher than that of the GO membrane. Moreover, the GO/SC[n]A membranes remained stable in wet state, along with a 66% elevation in mechanical performance compared to the GO membrane.

Covalent organic framework membranes through a mixed-dimensional assembly for molecular separations

Covalent organic frameworks (COFs) hold great promise in molecular separations owing to their robust, ordered and tunable porous network structures. Currently, the pore size of COFs is usually much larger than most small molecules. Meanwhile, the weak interlamellar interaction between COF nanosheets impedes the preparation of defect-free membranes. Herein, we report a series of COF membranes through a mixed-dimensional assembly of 2D COF nanosheets and 1D cellulose nanofibers (CNFs). The pore size of 0.45-1.0 nm is acquired from the sheltering effect of CNFs, rendering membranes precise molecular sieving ability, besides the multiple interactions between COFs and CNFs elevate membrane stability. Accordingly, the membranes exhibit a flux of 8.53 kg m-2 h-1 with a separation factor of 3876 for n-butanol dehydration, and high permeance of 42.8 L m-2 h-1 bar-1 with a rejection of 96.8% for Na2SO4 removal. Our mixed-dimensional design may inspire the fabrication and application of COF membranes.

Designing UiO-66-Based Superprotonic Conductor with the Highest Metal-Organic Framework Based Proton Conductivity

Metal-organic framework (MOF) based proton conductors have received immense importance recently. The present study endeavors to design two post synthetically modified UiO-66-based MOFs and examines the effects of their structural differences on their proton conductivity. UiO-66-NH₂ is modified by reaction with sultones to prepare two homologous compounds, that is, PSM 1 and PSM 2, with SO₃H functionalization in comparable extent (Zr:S = 2:1) in both. However, the pendant alkyl chain holding the -SO₃H group is of different length. PSM 2 has longer alkyl chain attachment than PSM 1. This difference in the length of side arms results in a huge difference in proton conductivity of the two compounds. PSM 1 is observed to have the highest MOF-based proton conductivity (1.64 × 10^-1 S cm^-1) at 80 °C, which is comparable to commercially available Nafion, while PSM 2 shows significantly lower conductivity (4.6 × 10^-3 S cm^-1). Again, the activation energy for proton conduction is one of the lowest among all MOF-based proton conductors in the case of PSM 1, while PSM 2 requires larger activation energy (almost 3 times). This profound effect of variation of the chain length of the side arm by one carbon atom in the case of PSM 1 and PSM 2 was rather surprising and never documented before. This effect of the length of the side arm can be very useful to understand the proton conduction mechanism of MOF-based compounds and also to design better proton conductors. Besides, PSM 1 showed proton conductivity as high as 1.64 × 10^-1 S cm^-1 at 80 °C, which is the highest reported value to date among all MOF-based systems. The lability of the -SO₃H proton of the post synthetically modified UiO-66 MOFs has theoretically been determined by molecular electrostatic potential analysis and theoretical p K_a calculation of models of functional sites along with relevant NBO analyses.

Targeted filling of silica in Nafion by a modified in situ sol–gel method for enhanced fuel cell performance at elevated temperatures and low humidity

By facilely utilizing an ionic cluster as a nano-reactor, a silica network can be targeted filled in Nafion to increase the PEMFC performance at elevated temperatures and low humidity. Moreover, the stability of Nafion can be improved for the long-term operation of PEMFC under harsh conditions.

Fast Proton Conduction in Denatured Bovine Serum Albumin-Coated Nafion Membranes

Bovine serum albumin (BSA) is a globular soluble protein, which has been extensively used in biochemical engineering. BSA materials possess abundant hydrophilic charged amino acids, H-bonded networks, and various secondary structures, which has great potential in facilitating proton transfer. Herein, BSA-N117 (BSA-Nafion 117) membranes are conveniently and eco-friendly prepared by utilizing the adsorption and denaturation of BSA on the Nafion 117 surface. The morphology and secondary structures of the BSA layer are studied with field-emission scanning electron microscopy, atomic force microscopy, and Fourier transform infrared spectroscopy. BSA-N117 membranes show highly increased proton conductivity under various conditions, which could be attributed to the improved wettability, water uptake, and the denaturation of BSA. The in-plane proton conductivity of BSA-N117-5 reaches 0.3 and 0.06 S cm^-1 under 80 °C-95% RH and 100 °C-40% RH, respectively. The denaturation of BSA leads to the unfolding of α-helix structures and the formation of β-sheet structures. β-Sheet structures are more beneficial to proton conduction since β-sheet structures have stronger interactions with water molecules and protons could transport more directly in the parallel H-bonded network. Moreover, the denatured BSA modification layer could effectively help BSA-N117 membranes to possess higher selectivity and overcome the "trade-off" effect between proton conductivity and methanol resistance. The methanol permeability of BSA-N117 membranes is 1 order of magnitude lower than that of Nafion 117.

Combining In Silico Design and Biomimetic Assembly: A New Approach for Developing High-Performance Dynamic Responsive Bio-Nanomaterials

Major challenge remains in the design and fabrication of artificial hierarchical materials that mimic the structural and functional features of these natural materials. Here, a novel biomimetic strategy to assemble hierarchical materials from biological nanobuilding blocks is demonstrated. The constituents and structures of the materials are designed by multiscale modeling and then experimentally constructed by multiscale self-assembly. The resultant materials that consist of silk nanofibrils (SNFs), hydroxyapatite (HAP), and chitin nanofibrils (CNFs) show nacre-like structures with mechanical strength and toughness better than most natural nacre and nacre-like nanocomposites. In addition, these SNF/HAP:CNF nanocomposites can be programmed into "grab-and-release" actuators due to the gradient structure of the nanocomposites as well as the high water sensitivity of each of the components, and thusshow potential applications in the design of novel third-generation biomaterials for potential clinical applications. In addition, this "in silico design and biomimetic assembly" route represents a rational, low-cost, and efficient strategy for the design and preparation of robust, hierarchical, and functional nanomaterials to meet a variety of application requirements in bio-nanotechnologies.

Self-Healing Proton-Exchange Membranes Composed of Nafion-Poly(vinyl alcohol) Complexes for Durable Direct Methanol Fuel Cells

Proton-exchange membranes (PEMs) that can heal mechanical damage to restore original functions are important for the fabrication of durable and reliable direct methanol fuel cells (DMFCs). The fabrication of healable PEMs that exhibit satisfactory mechanical stability, enhanced proton conductivity, and suppressed methanol permeability via hydrogen-bonding complexation between Nafion and poly(vinyl alcohol) (PVA) followed by postmodification with 4-carboxybenzaldehyde (CBA) molecules is presented. Compared with pure Nafion, the CBA/Nafion-PVA membranes exhibit enhanced mechanical properties with an ultimate tensile strength of ≈20.3 MPa and strain of ≈380%. The CBA/Nafion-PVA membrane shows a proton conductivity of 0.11 S cm^-1 at 80 °C, which is 1.2-fold higher than that of a Nafion membrane. The incorporated PVA gives the CBA/Nafion-PVA membranes excellent proton conductivity and methanol resistance. The resulting CBA/Nafion-PVA membranes are capable of healing mechanical damage of several tens of micrometers in size and restoring their original proton conductivity and methanol resistance under the working conditions of DMFCs. The healing property originates from the reversibility of hydrogen-bonding interactions between Nafion and CBA-modified PVA and the high chain mobility of Nafion and CBA-modified PVA.

Composite Proton-Exchange Membrane with Highly Improved Proton Conductivity Prepared by in Situ Crystallization of Porous Organic Cage

Porous organic cage, a kind of newly emerging soluble crystalline porous material, is introduced to proton-exchange membrane by in situ crystallization. The crystallized Cage 3 with intrinsic water-meditated three-dimensional interconnected proton pathways working together with Nafion matrix generates a composite membrane with highly improved proton conductivity. Different from inorganic crystalline porous materials, like metal-organic frameworks, the organic porous material shows better compatibility with Nafion matrix due to the absence of inorganic elements. In addition, Cage 3 can absorb water up to 20.1 wt %, which effectively facilitates proton conduction under both high- and low-humidity conditions. Meanwhile, the selectivity of Nafion-Cage 3 composite membrane is also elevated upon the loading of Cage 3. The proton conductivity is evidently enhanced without obvious increased methanol permeability. At 90 °C and 95% RH, the proton conductivity of NC3-5 reaches 0.27 S·cm^-1, highly improved compared to 0.08 S·cm^-1 of recast Nafion under the same condition. This study offers a new strategy for modifying proton-exchange membrane with crystalline porous materials.

Sulfonated Poly(Arylene Ether Sulfone) and Perfluorosulfonic Acid Composite Membranes Containing Perfluoropolyether Grafted Graphene Oxide for Polymer Electrolyte Membrane Fuel Cell Applications

Sulfonated poly(arylene ether sulfone) (SPAES) and perfluorosulfonic acid (PFSA) composite membranes were prepared using perfluoropolyether grafted graphene oxide (PFPE-GO) as a reinforcing filler for polymer electrolyte membrane fuel cell (PEMFC) applications. PFPE-GO was obtained by grafting poly(hexafluoropropylene oxide) having a carboxylic acid end group onto the surface of GO via ring opening reaction between the carboxylic acid group in poly(hexafluoropropylene oxide) and the epoxide groups in GO, using 4-dimethylaminopyridine as a base catalyst. Both SPAES and PFSA composite membranes containing PFPE-GO showed much improved mechanical strength and dimensional stability, compared to each linear SPAES and PFSA membrane, respectively. The enhanced mechanical strength and dimensional stability of composite membranes can be ascribed to the homogeneous dispersion of rigid conjugated carbon units in GO through the increased interfacial interactions between PFPE-GO and SPAES/PFSA matrices.

Highly Hydroxide-Conductive Nanostructured Solid Electrolyte via Predesigned Ionic Nanoaggregates

The creation of interconnected ionic nanoaggregates within solid electrolytes is a crucial yet challenging task for fabricating high-performance alkaline fuel cells. Herein, we present a facile and generic approach to embedding ionic nanoaggregates via predesigned hybrid core-shell nanoarchitecture within nonionic polymer membranes as follows: (i) synthesizing core-shell nanoparticles composed of SiO₂/densely quaternary ammonium-functionalized polystyrene. Because of the spatial confinement effect of the SiO₂ "core", the abundant hydroxide-conducting groups are locally aggregated in the functionalized polystyrene "shell", forming ionic nanoaggregates bearing intrinsic continuous ion channels; (ii) embedding these ionic nanoaggregates (20-70 wt %) into the polysulfone matrix to construct interconnected hydroxide-conducting channels. The chemical composition, physical morphology, amount, and distribution of the ionic nanoaggregates are facilely regulated, leading to highly connected ion channels with high effective ion mobility comparable to that of the state-of-the-art Nafion. The resulting membranes display strikingly high hydroxide conductivity (188.1 mS cm^-1 at 80 °C), which is one of the highest results to date. The membranes also exhibit good mechanical properties. The independent manipulation of the conduction function and nonconduction function by the ionic nanoaggregates and nonionic polymer matrix, respectively, opens a new avenue, free of microphase separation, for designing high-performance solid electrolytes for diverse application realms.

Novel Slightly Reduced Graphene Oxide Based Proton Exchange Membrane with Constructed Long-Range Ionic Nanochannels via Self-Assembling of Nafion

A facile method to prepare high-performance Nafion slightly reduced graphene oxide membranes (N-srGOMs) via vacuum filtration is proposed. The long-range connected ionic nanochannels in the membrane are constructed via the concentration-dependent self-assembling of the amphiphilic Nafion and the hydrophilic-hydrophobic interaction between graphene oxide (GO) and Nafion in water. The obtained N-srGOM possesses high proton conductivity, and low methanol permeability benefitted from the constructed unique interior structures. The proton conductivity of N-srGOM reaches as high as 0.58 S cm^-1 at 80 °C and 95%RH, which is near 4-fold of the commercialized Nafion 117 membrane under the same condition. The methanol permeability of N-srGOM is 2.0 × 10^-9 cm² s^-1, two-magnitude lower than that of Nafion 117. This novel membrane fabrication strategy has proved to be highly efficient in overcoming the "trade-off" effect between proton conductivity and methanol resistance and displays great potential in DMFC application.

Channel-facilitated molecule and ion transport across polymer composite membranes

This tutorial review highlights transport channels within polymer composite membranes and focuses on the regulation of channel microenvironments through bio-inspiration.