Bioinspired Graphene-Based Nanocomposites and Their Application in Flexible Energy Devices

Engineering of graphene-based composites with hexagonal boron nitride and PEDOT:PSS for sensing applications

A unique nanomaterial has been developed for sweat analysis, including glucose level monitoring. Simple resusable low-cost sensors from composite materials based on graphene, hexagonal boron nitride, and conductive PEDOT:PSS (poly(3,4-ethylenedioxythiophene)polystyrene sulfonate) polymer have been developed and fabricated via 2D printing on flexible substrates. The sensors were tested as biosensors using different water-based solutions. A strong increase in the current response (several orders of magnitude) was observed for aqua vapors or glucose solution vapors. This property is associated with the sorption capacity of graphene synthesized in a volume of plasma jets and thus having many active centers on the surface. The structure and properties of graphene synthesized in a plasma are different from those of graphene created by other methods. As a result, the current response for a wearable sensor is 3-5 orders of magnitude higher for the reference blood glucose concentration range of 4-14 mM. It has been found that the most promising sensor with the highest response was fabricated based on the graphene:PEDOT:PSS composite. The graphene:h-BN:PEDOT:PSS (h-BN is hexagonal boron nitride) sensors demonstrated a longer response and the highest response after the functionalization of the sensors with a glucose oxidase enzyme. The reusable wearable graphene:PEDOT:PSS glucose sensors on a paper substrate demonstrated a current response of 10-10 to 10-5 A for an operating voltage of 0.5 V and glucose range of 4-10 mM.

A 30-Year Review on Nanocomposites: Comprehensive Bibliometric Insights into Microstructural, Electrical, and Mechanical Properties Assisted by Artificial Intelligence

From 1990 to 2024, this study presents a groundbreaking bibliometric and sentiment analysis of nanocomposite literature, distinguishing itself from existing reviews through its unique computational methodology. Developed by our research group, this novel approach systematically investigates the evolution of nanocomposites, focusing on microstructural characterization, electrical properties, and mechanical behaviors. By deploying advanced Boolean search strategies within the Scopus database, we achieve a meticulous extraction and in-depth exploration of thematic content, a methodological advancement in the field. Our analysis uniquely identifies critical trends and insights concerning nanocomposite microstructure, electrical attributes, and mechanical performance. The paper goes beyond traditional textual analytics and bibliometric evaluation, offering new interpretations of data and highlighting significant collaborative efforts and influential studies within the nanocomposite domain. Our findings uncover the evolution of research language, thematic shifts, and global contributions, providing a distinct and comprehensive view of the dynamic evolution of nanocomposite research. A critical component of this study is the "State-of-the-Art and Gaps Extracted from Results and Discussions" section, which delves into the latest advancements in nanocomposite research. This section details various nanocomposite types and their properties and introduces novel interpretations of their applications, especially in nanocomposite films. By tracing historical progress and identifying emerging trends, this analysis emphasizes the significance of collaboration and influential studies in molding the field. Moreover, the "Literature Review Guided by Artificial Intelligence" section showcases an innovative AI-guided approach to nanocomposite research, a first in this domain. Focusing on articles from 2023, selected based on citation frequency, this method offers a new perspective on the interplay between nanocomposites and their electrical properties. It highlights the composition, structure, and functionality of various systems, integrating recent findings for a comprehensive overview of current knowledge. The sentiment analysis, with an average score of 0.638771, reflects a positive trend in academic discourse and an increasing recognition of the potential of nanocomposites. Our bibliometric analysis, another methodological novelty, maps the intellectual domain, emphasizing pivotal research themes and the influence of crosslinking time on nanocomposite attributes. While acknowledging its limitations, this study exemplifies the indispensable role of our innovative computational tools in synthesizing and understanding the extensive body of nanocomposite literature. This work not only elucidates prevailing trends but also contributes a unique perspective and novel insights, enhancing our understanding of the nanocomposite research field.

The Need for Smart Materials in an Expanding Smart World: MXene-Based Wearable Electronics and Their Advantageous Applications

As a result of the transformation of inflexible electronic structures into flexible and stretchy devices, wearable electronics now provide great advantages in a variety of fields, including mobile healthcare sensing and monitoring, human-machine interfaces, portable energy storage and harvesting, and more. Because of their enriched surface functionalities, large surface area, and high electrical conductivity, transition metal nitrides and carbides (also known as MXenes) have recently come to be extensively considered as a group of functioning two-dimensional nanomaterials as well as exceptional fundamental elements for forming flexible electronics devices. This Review discusses the most recent advancements that have been made in the field of MXene-enabled flexible electronics for wearable electronics. The emphasis is placed on extensively established nonstructural features in order to highlight some MXene-enabled electrical devices that were constructed on a nanometric scale. These attributes include devices configured in three dimensions: printed materials, bioinspired structures, and textile and planar substrates. In addition, sample applications in electromagnetic interference (EMI) shielding, energy, healthcare, and humanoid control of machinery illustrate the exceptional development of these nanodevices. The increasing potential of MXene nanoparticles as a new area in next-generation wearable electronic technologies is projected in this Review. The design challenges associated with these electronic devices are also discussed, and possible solutions are presented.

Two-dimensional Janus pentagonal MSeTe (M = Ni, Pd, Pt): promising water-splitting photocatalysts and optoelectronic materials

Inspired by the interesting and novel properties exhibited by Janus transition metal dichalcogenides (TMDs) and two-dimensional pentagonal structures, we here investigated the structural stability, mechanical, electronic, photocatalytic, and optical properties for a class of two-dimensional (2D) pentagonal Janus TMDs, namely penta-MSeTe (M = Ni, Pd, Pt) monolayers, by using density functional theory (DFT) combined with Hubbard's correction (U). Our results showed that these monolayers exhibit good structural stability, appropriate band structures for photocatalysts, high visible light absorption, and good photocatalytic applicability. The calculated electronic properties reveal that the penta-MSeTe are semiconductors with a bandgap range of 2.06-2.39 eV, and their band edge positions meet the requirements for water-splitting photocatalysts in various environments (pH = 0-13). We used stress engineering to seek higher solar-to-hydrogen (STH) efficiency in acidic (pH = 0), neutral (pH = 7) and alkaline (pH = 13) environments for penta-MSeTe from 0% to +8% biaxial and uniaxial strains. Our results showed that penta-PdSeTe stretched 8% along the y direction and demonstrates an STH efficiency of up to 29.71% when pH = 0, which breaks the theoretical limit of the conventional photocatalytic model. We also calculated the optical properties and found that they exhibit high absorption (13.11%) in the visible light range and possess a diverse range of hyperbolic regions. Hence, it is anticipated that penta-MSeTe materials hold great promise for applications in photocatalytic water splitting and optoelectronic devices.

Electric, magnetic, and shear field-directed assembly of inorganic nanoparticles

Ordered assemblies of inorganic nanoparticles (NPs) have shown tremendous potential for wide applications due to their unique collective properties, which differ from those of individual NPs. Various assembly methods, such as external field-directed assembly, interfacial assembly, template assembly, biomolecular recognition-mediated assembly, confined assembly, and others, have been employed to generate ordered inorganic NP assemblies with hierarchical structures. Among them, the external field-directed assembly method is particularly fascinating, as it can remotely assemble NPs into well-ordered superstructures. Moreover, external fields (e.g., electric, magnetic, and shear fields) can introduce a local and/or global field intensity gradient, resulting in an additional force on NPs to drive their rotation and/or translation. Therefore, the external field-directed assembly of NPs becomes a robust method to fabricate well-defined functional materials with the desired optical, electronic, and magnetic properties, which have various applications in catalysis, sensing, disease diagnosis, energy conversion/storage, photonics, nano-floating-gate memory, and others. In this review, the effects of an electric field, magnetic field, and shear field on the organization of inorganic NPs are highlighted. The methods for controlling the well-ordered organization of inorganic NPs at different scales and their advantages are reviewed. Finally, future challenges and perspectives in this field are discussed.

Benefits of Printed Graphene with Variable Resistance for Flexible and Ecological 5G Band Antennas

The possibility of creating antennas of the 5G standard (5.2-5.9 GHz) with specified electrodynamic characteristics by printing layers of variable thickness using a graphene suspension has been substantiated experimentally and by computer simulation. A graphene suspension for screen printing on photographic paper and other flexible substrates was prepared by means of exfoliation from graphite. The relation between the graphene layer thickness and its sheet resistance was studied with the aim of determining the required thickness of the antenna conductive layer. To create a two-sided dipole, a technology has been developed for the double-sided deposition of graphene layers on photographic paper. The electrodynamic characteristics of graphene and copper antennas of identical design are compared. The antenna design corresponds to the operating frequency of 2.4 GHz. It was found that the use of graphene as a conductive layer made it possible to suppress the fundamental (first) harmonic (2.45 GHz) and to observe radiation at the second harmonic (5.75 GHz). This effect is assumed to observe in the case when the thickness of graphene is lower than that of the skin depth. The result indicates the possibility of changing the antenna electrodynamic characteristics by adjusting the graphene layer thickness.

Graphene: Hexagonal Boron Nitride Composite Films with Low-Resistance for Flexible Electronics

The structure and electric properties of hexagonal boron nitride (h-BN):graphene composite with additives of the conductive polymer PEDOT:PSS and ethylene glycol were examined. The graphene and h-BN flakes synthesized in plasma with nanometer sizes were used for experiments. It was found that the addition of more than 10-3 mass% of PEDOT:PSS to the graphene suspension or h-BN:graphene composite in combination with ethylene glycol leads to a strong decrease (4-5 orders of magnitude, in our case) in the resistance of the films created from these suspensions. This is caused by an increase in the conductivity of PEDOT:PSS due to the interaction with ethylene glycol and synergetic effect on the composite properties of h-BN:graphene films. The addition of PEDOT:PSS to the h-BN:graphene composite leads to the correction of the bonds between nanoparticles and a weak change in the resistance under the tensile strain caused by the sample bending. A more pronounced flexibility of the composite films with tree components is demonstrated. The self-organization effects for graphene flakes and polar h-BN flakes lead to the formation of micrometer sized plates in drops and uniform-in-size nanoparticles in inks. The ratio of the components in the composite was found for the observed strong hysteresis and a negative differential resistance. Generally, PEDOT:PSS and ethylene glycol composite films are promising for their application as electrodes or active elements for logic and signal processing.

Ultrarobust Photothermal Materials via Dynamic Crosslinking for Solar Harvesting

Highly efficient and mechanically durable photothermal materials are urgently needed for solar harvesting, but their development still remains challenging. Here, inspired by the hierarchically oriented architecture of natural spider silk, an ultrarobust liquid metals (LMs)/polymer composite is presented via dynamic crosslinking based on the unique mechanical deformable characteristic of LMs. Dynamically cross-linked core-shell structured LMs droplets can be squeezed along with the orientational crystallization of polymer chains during drawing, thus enabling LMs nanoparticles to be uniformly programmed in the rigid polyethylene nanofiber skeleton. The resultant composite exhibits an unprecedented combination of strong broad-band light absorption (96.9-99.3%), excellent photothermal conversion ability, remarkable mechanical property (tensile strength of 283.7 MPa, which can lift 200 000 times its own weight), and long-term structural reliability (bearing 100 000 bending cycles). A powerful and durable solar thermoelectric generator system for real-environmental solar-heat-electricity conversion is further demonstrated, providing a valuable guidance for the design and fabrication of high-performance solar-harvesting materials.

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.

Advancement in Graphene-Based Materials and Their Nacre Inspired Composites for Armour Applications-A Review

The development of armour systems with higher ballistic resistance and light weight has gained considerable attention as an increasing number of countries are recognising the need to build up advanced self-defence system to deter potential military conflicts and threats. Graphene is a two dimensional one-atom thick nanomaterial which possesses excellent tensile strength (130 GPa) and specific penetration energy (10 times higher than steel). It is also lightweight, tough and stiff and is expected to replace the current aramid fibre-based polymer composites. Currently, insights derived from the study of the nacre (natural armour system) are finding applications on the development of artificial nacre structures using graphene-based materials that can achieve high toughness and energy dissipation. The aim of this review is to discuss the potential of graphene-based nanomaterials with regard to the penetration energy, toughness and ballistic limit for personal body armour applications. This review addresses the cutting-edge research in the ballistic performance of graphene-based materials through theoretical, experimentation as well as simulations. The influence of fabrication techniques and interfacial interactions of graphene-based bioinspired polymer composites for ballistic application are also discussed. This review also covers the artificial nacre which is shown to exhibit superior mechanical and toughness behaviours.

High-strength scalable graphene sheets by freezing stretch-induced alignment

Efforts to obtain high-strength graphene sheets by near-room-temperature assembly have been frustrated by the misalignment of graphene layers, which degrades mechanical properties. While in-plane stretching can decrease this misalignment, it reappears when releasing the stretch. Here we use covalent and π-π inter-platelet bridging to permanently freeze stretch-induced alignment of graphene sheets, and thereby increase isotropic in-plane sheet strength to 1.55 GPa, in combination with a high Young's modulus, electrical conductivity and weight-normalized shielding efficiency. Moreover, the stretch-bridged graphene sheets are scalable and can be easily bonded together using a commercial resin without appreciably decreasing the performance, which establishes the potential for practical applications.

Chemical Strategies for Making Strong Graphene Materials

Graphene materials have been widely applied in various fields because of their remarkable mechanical and electrical properties. However, two obstacles arise during the assembly of graphene platelets into macroscale graphene materials and composites that impair the performance of the resultant graphene materials: 1) the voids between the graphene platelets, and 2) the wrinkling of the graphene platelets. In the past decade, several strategies have been developed to eliminate these obstacles. These strategies result in strong macroscale graphene materials, such as graphene fibers with tensile strengths of over 3.4 GPa and sheets with tensile strengths of over 1.5 GPa, which have many practical applications. This Minireview summarizes the effective strategies for assembling graphene materials and compares their advantages and drawbacks. The preparation processes as well as the resulting fundamental mechanical properties and wide spectrum of electrical and magnetic properties are also discussed. Finally, our outlook for the future of this field is presented.

Ultratough and ultrastrong graphene oxide hybrid films via a polycationitrile approach

Graphene oxide (GO) is a classic two dimensional (2D) building block that can be used to develop high-performance materials for numerous applications, particularly in the energy and environmental fields. Currently, the precise assembly of GO nanosheets into macroscopic nanohybrids of superior strength and toughness is desirable, and faces challenges and trade-offs. Herein, we exploited the freshly established polycationitrile method as a powerful molecular crosslinking strategy to engineer ultratough and ultrastrong GO/polymer hybrid films, in which a covalent triazine-based network was constructed in a mild condition to reinforce the interface between GO nanosheets. The tensile strength and toughness reached 585 ± 25 MPa and 14.93 ± 1.09 MJ m^-3, respectively, which, to the best of our knowledge, are the current world records in all GO-based hybrid films. As an added merit of the tailor-made polymer crosslinker, the high mechanical performance can be maintained in large part at an extremely high relative humidity of 98%. This emerging interface-engineering approach paves a new avenue to produce integrated strong-and-tough 2D nanohybrid materials that are useful in aerospace, artificial muscle, energy harvesting, tissue engineering and more.

Recent Progress in Graphene/Polymer Nanocomposites

Nanocomposites, multiphase solid materials with at least one nanoscaled component, have been attracting ever-increasing attention because of their unique properties. Graphene is an ideal filler for high-performance multifunctional nanocomposites in light of its superior mechanical, electrical, thermal, and optical properties. However, the 2D nature of graphene usually gives rise to highly anisotropic features, which brings new opportunities to tailor nanocomposites by making full use of its excellent in-plane properties. Here, recent progress on graphene/polymer nanocomposites is summarized with emphasis on strengthening/toughening, electrical conduction, thermal transportation, and photothermal energy conversion. The influence of the graphene configuration, including layer number, defects, and lateral size, on its intrinsic properties and the properties of graphene/polymer nanocomposites is systematically analyzed. Meanwhile, the role of the interfacial interaction between graphene and polymer in affecting the properties of nanocomposites is also explored. The correlation between the graphene distribution in the matrix and the properties of the nanocomposite is discussed in detail. The key challenges and possible solutions are also addressed. This review may provide a constructive guidance for preparing high-performance graphene/polymer nanocomposite in the future.

Ordered polymer composite materials: challenges and opportunities

Polymer nanocomposites containing nanoscale fillers are an important class of materials due to their ability to access a wide variety of properties as a function of their composition. In order to take full advantage of these properties, it is critical to control the distribution of nanofillers within the parent polymer matrix, as this structural organization affects how the two constituent components interact with one another. In particular, new methods for generating ordered arrays of nanofillers represent a key underexplored research area, as emergent properties arising from nanoscale ordering can be used to introduce novel functionality currently inaccessible in random composites. The knowledge gained from developing such methods will provide important insight into the thermodynamics and kinetics associated with nanomaterial and polymer assembly. These insights will not only benefit researchers working on new composite materials, but will also deepen our understanding of soft matter systems in general. In this review, we summarize contemporary research efforts in manipulating nanofiller organization in polymer nanocomposites and highlight future challenges and opportunities for constructing ordered nanocomposite materials.

Nacre-Inspired Black Phosphorus/Nanofibrillar Cellulose Composite Film with Enhanced Mechanical Properties and Superior Fire Resistance

Natural nacre offers an optimized guiding principle for the assembly of lightweight and high-strength nanocomposites with excellent mechanical properties. Inspired by the "brick-and-mortar" layered structure of natural nacre, we present a cohort of bioinspired nanocomposites consisting of nanofibrillar cellulose (NFC) and few-layer hydroxyl functionalized black phosphorus (BP-OH) via a vacuum-assisted filtration self-assembly procedure. Owing to the well dispersed two-dimensional (2D) BP-OH in one-dimensional (1D) NFC and strong interfacial hydrogen bonding between them, these novel nacre-like BP-OHx/NFC composite films show excellent mechanical performance with tensile strength up to 214.0 MPa, 300% increase compared to pure NFC and tensile fracture strain up to 23.8%, 1.8 times higher than that of pure NFC. Moreover, these nacre-like composite films bare good fire resistance and high thermal stability. This nacre-inspired approach demonstrates a promising strategy for designing high-performance BP-OHx/NFC composite film, and the obtained bioinspired material could be a potential candidate in the application of flexible construction materials and flame retarded insulation materials.

Metal-Level Robust, Folding Endurance, and Highly Temperature-Stable MXene-Based Film with Engineered Aramid Nanofiber for Extreme-Condition Electromagnetic Interference Shielding Applications

Polymer-based electromagnetic interference (EMI) shielding materials possess many irreplaceable advantages than metals, such as superior flexibility, easy processing, and low density. However, impeded by their limited mechanical properties, inferior temperature resistance and unsatisfactory electrical conductivity, it is still challenging to extend their shielding applications under some extreme conditions, i.e., <-50 or >200 °C. Herein, we report an ultrathin, highly robust, superflexible, and temperature-stable film via engineering a worm-like aramid nanofiber (ANF) into the rod-like microscopic configuration, followed with self-assembly with Ti₃C₂T_x (MXene) into a hierarchical brick-and-mortar architecture. With stiff and symmetric aromatic rings fully straightened and well packed into a crystalline form in the backbone, this rod-like ANF enables an augmented network with effective energy dissipation, resulting in the metal-like mechanical properties, i.e., unprecedented tensile strength (300.5 MPa), high Young's modulus (13.6 GPa), and excellent folding endurance (>10 000 times). More significantly, this MXene/ANF composite film with outstanding specific EMI shielding effectiveness (8814.5 dB cm² g^-1) and flame retardancy performs a broad range of operations in the temperature range from -100 °C (355 MPa) to 300 °C (136 MPa), in which >99% electromagnetic waves could be eliminated; this promises its potential EMI shielding applications even in some extreme conditions.

Two-Dimensional Black Phosphorus: An Emerging Anode Material for Lithium-Ion Batteries

Two-dimensional black phosphorus (2D BP), an emerging material, has aroused tremendous interest once discovered. This is due to the fact that it integrates unprecedented properties of other 2D materials, such as tunable bandgap structures, outstanding electrochemical properties, anisotropic mechanical, thermodynamic, and photoelectric properties, making it of great research value in many fields. The emergence of 2D BP has greatly promoted the development of electrochemical energy storage devices, especially lithium-ion batteries. However, in the application of 2D BP, there are still some problems to be solved urgently, such as the difficulty in the synthesis of large-scale high-quality phosphorene, poor environmental stability, and the volume expansion as electrode materials. Herein, according to the latest research progress of 2D BP in the field of energy storage, we systematically summarize and compare the preparation methods of phosphorene and discuss the basic structure and properties of BP, especially the environmental instability and passivation techniques. In particular, the practical application and challenges of 2D BP as anode material for lithium-ion batteries are analyzed in detail. Finally, some personal perspectives on the future development and challenges of BP are presented.

Fabricating High-Resolution Metal Pattern with Inkjet Printed Water-Soluble Sacrificial Layer

The metal pattern plays a crucial role in various optoelectronic devices. However, fabrication of high-resolution metal patterns has serious problems including complicated techniques and high cost. Herein, an inkjet printed water-soluble sacrificial layer was proposed to fabricate a high-resolution metal pattern. The water-soluble sacrificial layer was inkjet printed on a polyethylene glycol terephthalate (PET) surface, and then the printed surface was deposited with a metal layer by evaporating deposition. When the deposited surface was rinsed by water, the metal layer deposited on the water-soluble sacrificial layer could be removed. Various high-resolution metal patterns were prepared, which could be used in electroluminescent displays, strain sensors, and 3D switches. This facile method could be a promising approach for fabricating high-resolution metal patterns.

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.

Coordination-Driven Hierarchical Assembly of Hybrid Nanostructures Based on 2D Materials

2D materials have received tremendous scientific and engineering interests due to their remarkable properties and broad-ranging applications such as energy storage and conversion, catalysis, biomedicine, electronics, and so forth. To further enhance their performance and endow them with new functions, 2D materials are proposed to hybridize with other nanostructured building blocks, resulting in hybrid nanostructures with various morphologies and structures. The properties and functions of these hybrid nanostructures depend strongly on the interfacial interactions between 2D materials and other building blocks. Covalent and coordination bonds are two strong interactions that hold high potential in constructing these robust hybrid nanostructures based on 2D materials. However, most 2D materials are chemically inert, posing problems for the covalent assembly with other building blocks. There are usually coordination atoms in most of 2D materials and their derivatives, thus coordination interaction as a strong interfacial interaction has attracted much attention. In this review, recent progress on the coordination-driven hierarchical assembly based on 2D materials is summarized, focusing on the synthesis approaches, various architectures, and structure-property relationship. Furthermore, insights into the present challenges and future research directions are also presented.

Highly flexible and mechanically strong polyaniline nanostructure @ aramid nanofiber films for free-standing supercapacitor electrodes

A key challenge for the fabrication of flexible electrochemical capacitors is to prepare robust electrode materials with excellent integration of high specific capacitances and superior mechanical properties. Aramid nanofibers (ANFs) are emerging candidates for constructing flexible electrode materials due to their superior mechanical properties. However, the present ANF based electrode materials are generally designed by mixing ANFs with electrochemically active components, which results in an unfavorable trade-off in mechanical and electrochemical properties. In this work, we reported flexible, mechanically strong, and free-standing supercapacitor electrodes based on polyaniline (PANI) nanostructure functionalized ANF films for the first time. The flexible PANI@ANF film electrodes achieved an efficient combination of mechanical and electrochemical performance in a single platform with a specific capacitance of 441.0 F g^-1 at a current density of 1 A g^-1 and a tensile strength of 233.3 MPa, respectively. This kind of free-standing electrode material may have great potential in the development of flexible energy-storage devices. Furthermore, we anticipate that this study may provide insight into the functionalization of aramid nanofiber-based materials for structural energy and power systems with high mechanical performance.

Co-incorporation of graphene oxide/silver nanoparticle into poly-L-lactic acid fibrous: A route toward the development of cytocompatible and antibacterial coating layer on magnesium implants

Magnesium (Mg) alloys present great potential for the development of orthopedic implants, whereas, their high degradation rate and poor antibacterial performance have restricted orthopedic applications. In this work, PLLA/GO-AgNP (poly-L-lactic acid/graphene oxide- silver nanoparticle) with different concentration of GO-AgNPs were deposited on Mg alloy via electrospinning method for enhancement of corrosion resistance and antibacterial performance. The result revealed that incorporation of GO into PLLA fibrous considerably slowed down the degradation rate of Mg alloy substrate and reduced the H₂ release rate from the substrate. Also, co-incorporation of GO and AgNPs into PLLA fibrous resulted in substantial escalate in compressive strength after immersion in simulated body fluid (SBF). Antibacterial activity test exhibited that Mg alloy and neat PLLA fibrous presented minimal inhibition area toward Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus). In contrast, using PLLA/GO-AgNPs fibrous improved antibacterial performance against both bacteria. Cytocompatibility results indicated that PLLA/GO-AgNPs fibrous with a low amount of GO-AgNPs enhanced cell proliferation and growth while high co-incorporation of GO-AgNPs showed a negative effect on cell proliferation. Taken together, PLLA/1GO-AgNPs fibrous coating shows suitable corrosion resistance, cytocompatibility, and antibacterial function for use in orthopedic applications.

Graphene-Based Fibers: Recent Advances in Preparation and Application

Graphene-based fibers (GBFs) are macroscopic 1D assemblies formed by using microscopic 2D graphene sheets as building blocks. Their unique structure exhibits the same merits as graphene such as low weight, high specific surface area, excellent mechanical/electrical properties, and ease of functionalization. Furthermore, the fibrous nature of GBFs is intrinsically compatible with existing textile technologies, making them suitable for applications in flexible and wearable electronics. Recently, novel synthetic methods have endowed GBFs with new structures and functions, further improving their mechanical and electrical properties. These improvements have rapidly bridged the gaps between laboratory demonstrations and real-life applications in fiber-shaped batteries, supercapacitors, and electrochemical sensors. Recent advances in the fabrication, optimization, and application of GBFs are systematically reviewed and a perspective on their future development is given.

Constructing reduced graphene oxide/boron nitride frameworks in melamine foam towards synthesizing phase change materials applied in thermal management of microelectronic devices

Phase change materials (PCMs) exhibit wide application prospects in many fields related to energy utilization and management and attract increasing interest. In this work, through the graphene oxide (GO)-assisted dispersion technology, GO/boron nitride (BN) nanosheets were incorporated into melamine foam and successfully deposited on the surface of the foam framework after hydrothermal reaction. Through the following freeze-drying and carbonization treatment, the composite MF/rGO/BN aerogels were obtained with integrated hybrid rGO/BN frameworks. The composite PCMs were prepared through encapsulating polyethylene glycol (PEG) within the hybrid aerogels. The encapsulation stability and thermal properties of the composite PCMs were systematically investigated. The composite PCM sample containing the highest content of rGO/BN exhibited excellent encapsulation stability, high thermal conductivity (up to 0.79 W m^-1 K^-1), high phase change enthalpy (160.7 J g^-1) with the retention of 90.8% of the pure PEG, and excellent chemical and thermal stability. Further results clearly showed that the composite PCMs had excellent light-to-heat energy transition ability and could be used as a thermal management component to suppress the overheating of devices during the operation process, or to supply energy for thermoelectric devices under emergency conditions to ensure a continuous power supply sustained for a certain time until the safeguard procedures are adopted.

Nanoscale toughening of ultrathin graphene oxide-polymer composites: mechanochemical insights into hydrogen-bonding/van der Waals interactions, polymer chain alignment, and steric parameters

This paper describes a systematic study on the nanoscale toughening of monolayer graphene oxide (GO) by an ultra-thin polymer adlayer, which impedes the propagation of cracks during intraplanar fracture. Using molecular dynamics simulations, the crack-bridging capabilities of a library of five hydrogen-bonding-capable polymers are explored against an epoxide-rich GO substrate. The best crack-bridging effect is found in polymers with functional groups that can both donate/accept hydrogen atoms and have better capability to form cooperative hydrogen bonds. Aligning the chains of poly(acrylic acid) orthogonally to the crack propagation direction significantly enhances the fracture toughness of monolayer GO (by 310%) in comparison to that for an adlayer with randomly arranged chains (180% enhancement). Notably, van der Waals interactions, which are seldom highlighted in the fabrication of strong GO-polymer interfaces, are found to also provide significant crack-bridging capabilities when the polymers possess large side groups. These results pave the way for a set of design criteria that can help in remediating the intrinsically brittle mechanical behavior of two-dimensional materials, a barrier that currently restricts their potential applications.

A green approach to fabricating nacre-inspired nanocoating for super-efficiently fire-safe polymers via one-step self-assembly

Developing a high efficient, environmental-friendly and universal fire-safe strategy for combustible polymers is crucial but challengeable. Inspired by nacre, we developed a super-efficiently fire-safe nanocoating based on carboxymethyl chitosan (CCS) and modified montmorillonite (MMT) via one-step self-assembly. The nanocoating possessed well-arranged nacre-like hierarchical microstructure, exhibiting high transparency and specific nacre-like iridescence. More importantly, the nanocoating endowed many large-scale polymer substrates, such as polyester film, cotton fabric and polyurethane foam, with super-efficient fire-safety by dip-coating or spray-coating. All the coated substrates were self-extinguished in the burning tests. Meanwhile, their heat release and smoke production were decreased remarkably. Most notably, the peak heat release rate, total heat release, peak smoke production rate and total smoke production of polyurethane foam were decreased by 84.1%, 89.4%, 84.4% and 95.2%, respectively. Additionally, no organic solvent, halogen and phosphorus element were involved, which was environmental-friendly. Our findings provide a super-efficient, economical, universal and green fabrication strategy for fire-safe polymers.

Free-Standing Black Phosphorus Thin Films for Flexible Quasi-Solid-State Micro-Supercapacitors with High Volumetric Power and Energy Density

Micro-supercapacitors (micro-SCs) are significant micro-scale power sources and energy storage components for miniaturized electronic and flexible devices, where electrodes play a key role in determining their electrochemical performances. The efficient intercalation of ions between the stacking layers of two-dimensional layered materials (2DLM) makes them great candidates as thin-film electrodes in micro-SCs, where one can achieve much enhanced volumetric capacitance. However, a great challenge is to develop a high-yield production method for high-quality 2DLM thin-film electrodes. In this work, we have successfully reported a scalable fabrication process for free-standing black phosphorous (BP) thin films, derived from high-quality few-layer BP nanoflakes via a modified electrochemical exfoliation route, for flexible quasi-solid-state micro-SCs (QMSCs). The as-fabricated QMSCs exhibit an excellent stable electrochemical performance at a high scan rate of up to 100 V s^-1. More importantly, our QMSC device can not only achieve an outstanding energy density of 3.63 mW h cm^-3, a remarkable power density of 10.1 W cm^-3, and a superior cycle span (94.3% capacity retention even after 50 000 cycles), but also deliver excellent mechanical flexibility demonstrated by 91.3% capacity retention after 500 mechanical bending cycles. More interestingly, to meet the energy density and power density needs for various practical applications, multiple QMSCs can be successfully integrated in parallel or in series, which is demonstrated by lighting up of the red-light-emitting diode. The BP-based QMSCs can be patterned on a single substrate with flexible photodetectors based on same BP thin film to form a self-powered optoelectronic system.

Ultratough Bioinspired Graphene Fiber via Sequential Toughening of Hydrogen and Ionic Bonding

Graphene-based fibers synthesized under ambient temperature have not achieved excellent mechanical properties of high toughness or tensile strength compared with those synthesized by hydrothermal strategy or graphitization and annealing treatment. Inspired by the relationship between organic/inorganic hierarchical structure, interfacial interactions, and moderate growth temperature of natural nacre, we fabricate an ultratough graphene fiber via sequential toughening of hydrogen and ionic bonding through a wet-spinning method under ambient temperature. A slight amount of chitosan is introduced to form hydrogen bonding with graphene oxide nanosheets, and the ionic bonding is formed between graphene oxide nanosheets and divalent calcium ions. The optimized sequential toughening of hydrogen and ionic bonding results in an ultratough graphene fiber with toughness of 26.3 MJ/m³ and ultimate tensile strength of 743.6 MPa. Meanwhile, the electrical conductivity of the resultant graphene fiber is as high as 179.0 S/cm. This kind of multifunctional graphene fiber shows promising applications in photovoltaic wires, flexible supercapacitor electrodes, wearable electronic textiles, fiber motors, etc. Furthermore, the strategy of sequential toughening of hydrogen and ionic bonding interactions also offers an avenue for constructing high-performance graphene-based fibers in the near future.

Efficient room-temperature production of high-quality graphene by introducing removable oxygen functional groups to the precursor

The excellent solution-processability of graphene oxide (GO) has provided a collection of strategies for the construction of functional graphene assemblies. To improve the performance of graphene-based materials, structurally intact GO should be prepared as a precursor for high-quality graphene; however, solution chemical methods have been constantly challenged by a structural integrity versus fabrication yield trade-off. Here, we report a wet chemical method for the high-efficiency production of a high-quality graphene oxide precursor, with all steps conducted at room-temperature. The functionalization of graphite was performed under temperature and water content control in a concentrated sulfuric acid-potassium permanganate system, and the resulting GO showed a monolayer yield of over 120%. We show that the increased production yield comes from the high functionalization degree and, more interestingly, the functional groups on GO were proven to be removable upon reduction with hydroiodic acid, which produced high-quality graphene-based materials.

Bioinspired Design of Strong, Tough, and Thermally Stable Polymeric Materials via Nanoconfinement

The combination of high strength, great toughness, and high heat resistance for polymeric materials is a vital factor for their practical applications. Unfortunately, until now it has remained a major challenge to achieve this performance portfolio because the mechanisms of strength and toughness are mutually exclusive. In the natural world, spider silk features the combination of high strength, great toughness, and excellent thermal stability, which are governed by the nanoconfinement of hydrogen-bonded β-sheets. Here, we report a facile bioinspired methodology for fabricating advanced polymer composite films with a high tensile strength of 152.8 MPa, a high stiffness of 4.35 GPa, and a tensile toughness of 30.3 MJ/m³ in addition to high thermal stability (69 °C higher than that of the polymer matrix) only by adding 2.0 wt % of artificial β-sheets. The mechanical and thermostable performance portfolio is superior to that of its counterparts developed to date because of the nanoconfinement and hydrogen-bond cross-linking effects of artificial β-sheets. Our study offers a facile biomimetic strategy for the design of integrated mechanically robust and thermostable polymer materials, which hold promise for many applications in electrical devices and tissue engineering fields.

Bioinspired Supertough Graphene Fiber through Sequential Interfacial Interactions

Natural nacre exhibits extraordinary functional and structural diversity, combining high strength and toughness. The mechanical properties of nacre are attributed to (i) a highly arranged hierarchical layered structure of inorganic minerals (95 vol %) containing a small amount only of organic materials (5 vol %), (ii) abundant synergistic interfacial interactions, and (iii) formation under ambient temperature. Herein, inspired by these three design principles originating from natural nacre, the supertough bioinspired graphene-based nanocomposite fibers (BGNFs) are prepared under room temperature via sequential interfacial interactions of ionic bonding and π-π interactions. The resultant synergistic effect leads to a super toughness of 18.7 MJ m^-3 as well as a high tensile strength of 740.1 MPa. In addition, the electrical conductivity of these supertough BGNFs is as high as 384.3 S cm^-1. They can retain almost 80% of this conductivity even after 1000 cycles of loading-unloading testing, which makes these BGNFs promising candidates for application in flexible and stable electrical devices, such as strain sensors and actuators.

A stepwise crosslinking strategy toward lamellar carbon frameworks with covalently connected alternate layers of porous carbon nanosheets and porous carbon spacers

Lamellar carbon frameworks with covalently connected alternate layers of porous carbon nanosheets (PCNs) and porous carbon spacers (PCSs) were successfully fabricated based on the stepwise crosslinking of self-assembled lamellar block copolymers. The intrinsic porous structure of PCSs can maximize the utilization of well-developed surfaces/interfaces of the PCNs.

Strong, Conductive, Foldable Graphene Sheets by Sequential Ionic and π Bridging

The goal of this work is to develop an inexpensive low-temperature process that provides polymer-free, high-strength, high-toughness, electrically conducting sheets of reduced graphene oxide (rGO). To develop this process, we have evaluated the mechanical and electrical properties resulting from the application of an ionic bonding agent (Cr3+ ), a π-π bonding agent comprising pyrene end groups, and their combinations for enhancing the performance of rGO sheets. When only one bonding agent was used, the π-π bonding agent is much more effective than the ionic bonding agent for improving both the mechanical and electrical properties of rGO sheets. However, the successive application of ionic bonding and π-π bonding agents maximizes tensile strength, toughness, long-term electrical stability in various corrosive solutions, and resistance to mechanical abuse and ultrasonic dissolution. Using a combination of ionic bonding and π-π bonding agents, high tensile strength (821 MPa), high toughness (20 MJ m-3 ), and electrical conductivity (416 S cm-1 ) were obtained, as well as remarkable retention of mechanical and electrical properties during ultrasonication and mechanical cycling by both sheet stretch and sheet folding, suggesting high potential for applications in aerospace and flexible electronics.

Gelation-Assisted Layer-by-Layer Deposition of High Performance Nanocomposites

Layer-by-layer (LBL) assembly produces nanocomposites with distinctively high volume fractions of nanomaterials and nanometer scale controlled uniformity. Although deposition of one nanometer scale layer at a time leads to high performance composites, this deposition mode is also associated with the slow multilayer build-up. Exponential LBL, spin coating, turbo-LBL and other methods tremendously accelerate the multilayer build-up but often yield lower, strength, toughness, conductivity, etc. Here, we introduce gelation assisted layer-by-layer (gaLBL) deposition taking advantage of a repeating cycle of hydrogel formation and subsequent polymer infiltration demonstrated using aramid nanofiber (ANF) and epoxy resin (EPX) as deposition partners. Utilization of ANF gels increases the thickness of each deposited layer from 1–10 nm to 30–300 nm while retaining fine control of thickness in each layer, high volume fraction, and uniformity. While increasing the speed of the deposition, the high density of interfaces associated with nanofiber gels helps retain high mechanical properties. The ANF/EPX multilayer composites revealed a rare combination of properties that was unavailable in traditional aramid-based and other composites, namely, high ultimate strength of 505±47 MPa, high toughness of 50.1±9.8 MJ/m3, and high transparency. Interestingly, the composite also displayed close-to-zero thermal expansion. The constellation of these materials properties is unique both for quasi-anisotropic composites and unidirectional materials with nanofiber alignment. gaLBL demonstrates the capability to resolve the fundamental challenge between high-performance and scalability. The gelation-assisted layered deposition can be extended to other functional components including nanoparticle gels.

Artificial Nacre from Supramolecular Assembly of Graphene Oxide

Inspired by the "brick-and-mortar" structure and remarkable mechanical performance of nacre, many efforts have been devoted to fabricating nacre-mimicking materials. Herein, a class of graphene oxide (GO) based artificial nacre material with quadruple hydrogen-bonding interactions was fabricated by functionalization of polydopamine-capped graphene oxide (PDG) with 2-ureido-4[1 H]-pyrimidinone (UPy) self-complementary quadruple hydrogen-bonding units followed by supramolecular assembly process. The artificial nacre displays a strict "brick-and-mortar" structure, with PDG nanosheets as the brick and UPy units as the mortar. The resultant nanocomposite shows an excellent balance of strength and toughness. Because of the strong strengthening via quadruple hydrogen bonding, the tensile strength and toughness can reach 325.6 ± 17.8 MPa and 11.1 ± 1.3 MJ m^-3, respectively, thus exceeding natural nacre, and reaching 3.6 and 10 times that of a pure GO artificial nacre. Furthermore, after further H₂O treatment, the resulting H₂O-treated PDG-UPy actuator displays significant bending actuations when driven by heat. This work provides a pathway for the development of artificial nacre for their potential applications in energy conversion, temperature sensor, and thermo-driven actuator.

Electrochemically Scalable Production of Fluorine-Modified Graphene for Flexible and High-Energy Ionogel-Based Microsupercapacitors

Scalable production of high-quality heteroatom-modified graphene is critical for microscale supercapacitors but remains a great challenge. Herein, we demonstrate a scalable, single-step electrochemical exfoliation of graphite into highly solution-processable fluorine-modified graphene (FG), achieved in an aqueous fluorine-containing neutral electrolyte, for flexible and high-energy-density ionogel-based microsupercapacitors (FG-MSCs). The electrochemically exfoliated FG nanosheets are characterized by atomic thinness, large lateral size (up to 12 μm), a high yield of >70% with ≤3 layers, and a fluorine doping of 3 at%, allowing for large-scale production of FG-MSCs. Our ionogel-based FG-MSCs deliver high energy density of 56 mWh cm^-3, by far outperforming the most reported MSCs. Furthermore, the all-solid-state microdevices offer exceptional cyclability with ∼93% after 5000 cycles, robust mechanical flexibility with 100% of capacitance retention bended at 180°, and outstanding serial and parallel integration without the requirement of metal-based interconnects for high-voltage and high-capacitance output. Therefore, these FG-MSCs represent remarkable potential for electronics.