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Ultrathin two-dimensional (2D) metal-organic framework (MOF) nanosheets (MOFNs) comprise an emerging family of attractive materials with excellent potential for use in different catalytic, electrochemical, and sensing applications owing to their striking features such as ultrathin thickness, a large surface area, and highly ordered network structures. However, to the best of our knowledge, the ligand-cluster units activated through exfoliation into the MOFNs have rarely been realized, which is indeed crucial for surface-enhanced Raman scattering (SERS) analysis. Herein, we emphasize that the activated ligand-cluster units are based on the accessible coordination sites at the exposed cluster nodes accompanied by a complete excitation of the ligand-cluster units under incident photons, which make MOFNs highly effective SERS substrates, significantly outperforming their bulk counterparts. The SERS enhancement of MOFNs is further illustrated by an efficient integration of the inherent ligand-cluster charge-transfer (LCCT) transitions in MOFNs into interfacial charge-transfer processes through an "L"-type charge-transfer (CT) pathway, as further evidenced by an ultrahigh degree (0.98) of CT contributed to the SERS enhancement. This study provides an efficient strategy of exfoliating MOFs into ultrathin nanosheets for the design of highly efficient MOF-based SERS substrates.

Harvesting and transforming water energy into electricity via nanostructured materials, which is termed hydrovoltaic power generation (HPG), has attracted increasing interest in the past few decades. However, the current limitation of HPG devices taking advantage of the electrokinetic effect is their poor power density within microwatts per square meter. Herein, a novel catalytic graphene aerogel film decorated with an interlayer catalyst of α-FeOOH was developed successfully. Upon the addition of H2O2 to a saline (NaCl) droplet, an exceptionally high voltage of 0.63 V was achieved, which is around 20 times higher than the previously reported value using single-layer graphene. The experimental and theoretical results showed that the high hydrovoltaic performance originates from three contributions. Firstly, the large droplet/graphene interfaces, benefitting from the high specific surface area of the aerogel and the bubbling effect produced by the catalytic decomposition of H2O2via α-FeOOH. Secondly, the enhanced electrokinetic effect, i.e., increased hydrated ion radius of NaCl and suppressed shielding effect between cations and anions in the presence of H2O2, which dramatically extends the NaCl concentration window from 0.6 M to 5.0 M. Thirdly, utilizing the advantage of electrochemical reactions related to H2O2 in the saline (NaCl) droplet to greatly increase the short-circuit current of the HPG device. The outcome of these contributions is a much higher ion utilization efficiency under a high saline concentration, which breaks the output bottleneck of power density caused by using a low saline concentration. Our work extends the device component from single-layer graphene to a 3D porous graphene aerogel, making a significant step forward for the future development of HPG devices.

In this work, transmission electron microscopy (TEM) was applied to study single-walled carbon nanotube (SWCNT) dispersion states in aqueous solutions at nanoscale, and a method based on selected-area electron diffraction patterns was developed to quantitatively describe the internal SWCNT alignment across a whole fiber. Moreover, the SWCNT bundle size and pore defects were also evaluated by high-resolution TEM. It was found that the SWCNT bundle size increased from approximately 15 to 40 nm as its mass concentration increased from 0.4% to 1.0% in the spinning dope, which then influenced the SWCNT bundle size in the final fibers. Meanwhile, the degree of SWCNT alignment in the fiber increased initially and then decreased monotonically with the increased concentration. The effects of spinning needle size and length on the mechanical performance of the fibers were also discussed. The combination of the nano-structural characterizations of the spinning dopes and the final fibers sheds some light on the development of high-performance CNT fibers.

The rational design and construction of high-performance fiber-shaped NiCo//Fe batteries is of great importance for the development of portable and wearable electronics. Electrode materials with all hierarchical core-shell heterostructures have great potential for use in high-performance NiCo//Fe batteries as a result of their good conductivity, high mass loading, and short ion-diffusion paths. Herein is proposed a novel freestanding core-shell positive and negative electrode materials developed by depositing NiCoP nanosheets on nanoflake arrays (NiCoP@NiCoP NFAs) and Fe2O3 nanoneedles on TiN nanowire arrays (TiN@Fe2O3 NWAs) directly grown on carbon nanotube fibers (CNTFs). The fabricated NiCoP@NiCoP NFAs/CNTF was validated to be an ultrahigh capacity cathode (1.07 mAh cm−2 at 2 ​mA ​cm−2), matching well with the similarly constructed TiN@Fe2O3 NWAs/CNTF anode (0.92 mAh cm−2 at 2 ​mA ​cm−2). These electrodes were successfully developed into a high-performance NiCo//Fe battery that exhibited an extraordinary capacity of 0.77 mAh cm−2 and a remarkable energy density of 265.2 ​mWh cm−3. The flexible battery demonstrated an excellent cycling lifespan with 89.4% capacity retention after 4000 cycles. This pioneering study describes a powerful strategy for the rational construction of high-performance electrode materials with hierarchical core-shell heterostructures and constitutes a novel approach for the development of new-generation wearable aqueous rechargeable batteries.

Internal asymmetric tandem supercapacitors with wide working voltage have drawn an increasing attention to develop high-energy-density supercapacitors. However, the small specific capacitance and low working voltage of single-supercapacitor restrict further improvement of their energy density. A rational solution to this restriction would be to synthesize high-performance electrode materials. Accordingly, this work specifies a simple and cost-effective method to directly grow manganese dioxide and vanadium nitrogen nanosheets on zeolitic imidazolate framework-67 derived N-doped carbon conductive skeletons. These well-designed core-shell pseudocapacitive materials integrate the features of large specific surface area, rich reaction sites, high mass loading, short electron/ion diffusion paths and remarkable conductivity, affording prominent electrochemical performance. Furthermore, a flexible all-solid-state internal asymmetric tandem 6.6 V all-in-one supercapacitor was successfully assembled by matching as-fabricated cathode and anode materials as well as using carbon nanotube film as a lightweight current collector. The resulting all-in-one devices exhibited a high specific capacitance of 336.7 mF/cm2 (19.6 F/cm3) and an exceptional energy density of 2032.8 μWh/cm2 (118.2 mWh/cm3) and thus substantially outperform most previously reported state-of-the-art asymmetric supercapacitors. Our work provides a promising strategy for the rational construction of high-performance, inexpensive and safe all-in-one supercapacitors for next-generation portable and wearable electronic devices. This work was supported by the National Natural Science Foundation of China (No. 51703241), the Fundamental Research Funds for the Central Universities (No. 020514380183), the Key Research Program of Frontier Science of Chinese Academy of Sciences (No. QYZDB-SSWSLH031), the Thousand Youth Talents Plan, and the Science and Technology Project of Nanchang (2017-SJSYS-008).

The self-assembly of cyclodextrins (CDs) with various guest polymers and small molecules has been intensively investigated for several decades, and it has still increasingly attracted wide attention to construct well-defined microstructures for the uses in biomedicine, sensors, environments, and nanorobotics. While most of the self-assembly of CDs involves the presence of guests, we recently discovered that α-CDs and γ-CDs could be self-assembled between themselves without the incorporation of any guests simply by elevating the temperature of their

The ability to shape and program remotely and contactlessly from two-dimensional (2D) flat multilayer materials into three-dimensional (3D) structures and functional devices could be ideal for applications like space missions, environmental remediation and minimally invasive surgery. However, achieving a fast and accurate deployment of complex 3D shapes contaclessly at low energy consumption, while embedding a number of physical properties and functionalities, remains very challenging. Herein, a strategy to widen the complexity space of 3D shapes and functions achievable is demonstrated, by enabling a controlled sequential folding while incorporating nano-reinforcements. Sequential folding was successfully achieved and a honeycomb structure was developed by designing multilayer polymer films with different kirigami patterns - each responding at a different rate upon heating. A finite element method (FEM) model was developed to better understand the main underlying physical mechanism as well as to feedback into materials and structure design. Moreover, a shape-programmed CNT veil-based honeycomb structure was developed, triggered remotely by thermal stimuli, with capability to self-sense the folding state through the electrical resistance change (ΔR/R0 = 100–300 %). Overall, it was demonstrated that designing layered nanocomposites with different 2D patterns allows an accurate sequential folding into 3D structures, with bespoke physical properties and integrated sensing–actuating functionalities.

A new approach for making carbon nanotube (CNT) films that are both strong and tough is detailed in this paper. Aqueous dispersions of long CNTs were first obtained by dispersing CNT arrays with heights of about 200 μm in deionized water with the help of polyvinylpyrrolidones (PVPs) and polydopamines (PDAs). CNT films were then obtained by vacuum-assisted filtration of CNT dispersions. The tensile strength and toughness of the composite films can be as high as 143.5 MPa and 5.0 MJ/m3, respectively, which was 330.7% and 213.8% higher than CNT films made without using PVPs and PDAs. The underlying mechanism of PVPs and PDAs induced CNT film strengthening and toughening was revealed through preliminary molecular dynamics simulations, which indicated that the hydrogen bonds between the PVPs and PDAs enhanced the strength of the film, and these bonds can cyclically break and reform, making CNT films tougher. The strategy proposed here can also be applied to making other nano-materials based strong and tough macro-assemblies.

The need for developing energy storage devices with high energy and power densities has motivated tremendous effort in the research of supercapacitors. Major challenges still exist in improving the working voltage window and specific capacitance of the devices. Here, we report a systematic effort in achieving remarkable supercapacitor performance. Firstly, a flexible CNT film/double side carbon tape/CNT film@MnO2 (CDC@MnO2) positive electrode with a large voltage window of 0–1.2 V was fabricated via a facial one-step water bath process. The large interfacial area created by the CDC sandwich structure enabled a high MnO2 mass loading up to 6.6 mg cm−2, resulting in a high area capacitance of 1.1 F cm−2 at a current density of 1 mA cm−2. Secondly, inspired by the superior electrochemical performance of the CDC@MnO2 positive electrode, a CDC@Fe2O3 film with area capacitance up to 339.1 mF cm−2 was fabricated as the negative electrode. Thirdly, a flexible asymmetric supercapacitor was successfully assembled which possesses a large voltage window of 0–2.1 V, a high volume capacitance of 6.8 F cm−3, and a high energy density of 4.1 mWh cm−3 at the power density of 22.3 mW cm−3.

Transition metal-nitrogen-carbon (M-N-C) catalysts have emerged as the most promising alternatives to their costly platinum–based counterparts for oxygen reduction reaction (ORR) catalysis, which are critical to renewable energy conversion and storage technologies. However, thus far, only 3d transition metals (Co, Fe, Ni, Mn, etc.) have often been good choices for the metal elements in such M-N-C catalysts, while other non-3d transition metals-based catalysts such as 5d tungsten (W) usually afford much inferior ORR activities in both bulk and nanoparticle form. Here, we report the atomically dispersed tungsten on nitrogen-doped carbon nanosheets with controlled W-N coordination numbers as efficient catalysts for ORRs, which are only formed through the deliberate modulation of the synthesis parameters, such as the pyrolysis atmosphere, temperature, and time, within a very narrow range. Instead of being considered to be almost inactive towards ORR, the single-atom tungsten electrocatalysts show remarkable, durable and coordination number-sensitive ORR catalytic ability. It is shown that single-atom tungsten with a W-N coordination number of 5 exhibits markedly high ORR catalytic activity in 0.1 M KOH with onset potential (∼1.01 V), half-wave potential (0.88 V) and a mass activity of 0.63 A/mg (at 0.9 V versus RHE), which even surpasses those of commercial Pt/C. Meanwhile, the WN5 catalyst catalyzes the ORR with a onset potential of 0.87 V and a half-wave potential of 0.77V in 0.1 M HClO4, both of which are nearly comparable to the benchmark Pt/C. In contrast, the single-atom tungsten electrocatalysts with W-N coordination numbers of 3 and 4 exhibit relatively poor ORR activity in both acidic and alkaline electrolytes. The DFT calculations suggest that the sharp increase in the ORR activity of the single-atom tungsten catalysts can be attributed to the moderate interaction between OH- and the single W atoms, which is probably caused by the optimal dz2-pz orbital hybridization and re-distribution of the charges.

Using boric acid (H3BO3) as a boron source and zinc acetate [Zn(Ac)2] as a release chemical, various boron nitride nanosheets (BNNSs) are synthesized in the presence of ammonia (NH3). The structures of the BNNSs are tuned by changing the preparation procedures and the mole ratios of H3BO3 and Zn(Ac)2. The results indicate that Zn(Ac)2 is an excellent template and release agent for the formation of BNNSs owing to the suitable decomposition temperature, the easy reduction of zinc oxide (ZnO) in NH3, and the relatively low boiling point of zinc (Zn). As two-dimensional layered materials, all of the prepared BNNSs can reduce the friction coefficient (FC) of pure water, and the large-area and thick nanosheets show better tribological performances than the small-area and thin nanosheets, possibly as a result of the weakened mechanical strength at the reduced sizes.

In this contribution we report an integrated method to obtain soluble boron nitride nanosheets (BNNSs) by combing ball-mill, chemical vapor deposition (CVD) growth, Lewis acid-base interaction, and ultrasonic exfoliation. This simple and inexpensive method can achieve a high yield of 40% few layer BNNSs. Based on the excellent dispersity in water and dimethylformamide (DMF), we introduced these nanosheets into thermoplastic polyurethane (TPU) to fabricate composite films, which display good uniformity and high thermal conductivity. The high-yield can be attributed to the synergistic effects of the multi-steps processing, while the good dispersity may be derived from the chemical functionalization and the formation of nanohybrids. The present method can promote the practical applications of BNNSs in many fields, especially the polymer-based nanocomposites.

Aerogel is a kind of high-performance lightweight open-porous solids with ultralow density, high specific surface area, and broad application in many emerging fields including biotechnology, energy, environment, aerospace, etc. A giant challenge remains in preventing of the hydrophilic aerogel framework shrinkage when replacing of solvent with air in its extremely abundant nanosized pores during its fabrication process in ambient conditions. In this work, started from a linear polymeric precursor with further condensation reaction, superhydrophilic silica aerogels with self-reinforced microstructure and the least volume shrinkage have been successfully obtained via ambient pressure drying process without use of any additives in the presence of a low surface tension solvent. The resulting superhydrophilic silica aerogels possess specific surface area up to 1065 m2/g, pore volume up to 2.17 cm3/g and density down to 84 mg/cm3, and these values are comparable to those of their counterparts obtained by supercritical CO2 drying process. Moreover, as an application demonstration, the bioinspired hydrogels with desirable mechanical flexibility and adhesive performance at extremely harsh environment (e.g., below -50 °C) have been successfully synthesized by mimicking carrier of a functional bioagent with the resulting superhydrophilic silica aerogel microparticles. Our work has made a significant step forward for future high-performance hydrophilic aerogels with self-enhanced microstructures and the resulting superhydrophilic aerogels have shown great potentials in making functional hydrogels with bionic properties.

Carbon nanotube (CNT) film has been considered as a promising preform of CNTs for developing high performance composites that possess high content of CNTs. However, due to the intertube van der Waals interactions, CNTs in the films are often tightly bundled together, making the impregnation of resin materials to CNTs very challenging. In this work, an eco-friendly ultrasonic-assisted resin infiltration process has been developed, and its effects on CNT bundles diameter, CNT crystallinity, CNT film stretchability, and the mechanical properties of CNT films and their based composites have been systematically investigated. It has been found that CNT bundles became thinner and the film stretchability became higher upon the ultrasonication, and thus the performance of CNT film-based composites were improved. However, extensive sonication would severely destroy the crystal structures of CNTs and thus degrade the mechanical properties of CNT films and their based composites. The underlying mechanisms for the evolution of CNT networks during the ultrasonic treatment were also discussed.

Different from conventional conductors, elastic 3D nanoarchitectured conductors have shown promise in developing various flexible devices. However, rational design and control of their microstructures to achieve desired physicochemical properties is challenging and lacks comprehensive and profound investigation. In this study, we report an interesting quantitative correlation between density and physical properties when highly porous CNT aerogels are densified, enabling a wide-range tuning of CNT 3D networked structures with different functions. Upon densification by compressing the original thickness of a CNT aerogel by 100 fold, a linear double-logarithmic structure-property relationship in terms of both thickness and density is witnessed, with the resultant density increased by a factor of 100 from 3 to 286 mg cm-3, Young's modulus by 20 times (5.0-105 kPa), electrical conductivity by 400 times (0.4-163 s cm-1), and thermal conductivity by 140 times (0.048-6.7 W m-1 K-1). It can be thus inferred that the CNT aerogel can be regulated with desired mechanical, electrical and thermal properties in a quantitative manner over a wide range, making it promising as a multifunctional aerogel conductor. As a proof, two pieces of CNT aerogel conductors tailored with high conductivity and low thermal conductivity are employed to fabricate a flexible TE device using a simple all-carbon design, which yields a typical power density of 27.5 μW cm-2 and stable outputs under various deformations, demonstrating a potential strategy for design and fabrication of low-cost, flexible and portable power-generation devices.

A variety of chroman-4-ones bearing phosphine oxide motifs were conveniently synthesized from readily available diphenylphosphine oxide and alkenyl aldehydes via a metal-free tandem phosphinoylation/cyclization protocol. The reaction utilizes K2S2O8 as oxidant and proceeds in DMSO-H2O at environmentally benign conditions with broad substrate scope and afforded the title compounds in moderate yields.

In this work, we have studied the uniaxial tension behaviors of the silicone–carbon nanotube (CNT) laminated structure (SCLS) with the load capacity of the CNT film comparable to that of silicone rubber, based on which a theoretical model is proposed to explore the underlying mechanism. The uniaxial tension behaviors of SCLS can be clearly divided into three stages corresponding to the uniform deformation of silicone rubber and CNT film, continuous fracture of CNT film, and uniaxial tension of silicone rubber, respectively. A zigzag plateau stress is observed in stage II. Indeed, the CNT film can act as a pinning ligament to constrain the deformation of silicone rubber, while its continuous fracture can gradually release the deformability of silicone rubber which is beneficial to increase the toughness of SCLS. By considering the in-plane tension stress of the CNT film and interface shear stress transfer, a continuous fracture and pinning model is proposed which can describe the uniaxial tension behaviors of SCLS very well. The results presented herein may shed useful insights for the design and optimization of the film-substrate based stretchable electronics.

Aqueous rechargeable Ni-Fe batteries featuring an ultra-flat discharge plateau, low cost, and outstanding safety characteristics show promising prospects for application in wearable energy storage. In particular, fiber-shaped Ni-Fe batteries will enable textile-based energy supply for wearable electronics. However, the development of fiber-shaped Ni-Fe batteries is currently challenged by the performance of fibrous Fe-based anode materials. In this context, this study describes the fabrication of sulfur-doped Fe2O3 nanowire arrays (S-Fe2O3 NWAs) grown on carbon nanotube fibers (CNTFs) as an innovative anode material (S-Fe2O3 NWAs/CNTF). Encouragingly, first-principle calculations reveal that S-doping in Fe2O3 can dramatically reduce the band gap from 2.34 to 1.18 eV and thus enhance electronic conductivity. The novel developed S-Fe2O3 NWAs/CNTF electrode is further demonstrated to deliver a very high capacity of 0.81 mAh cm−2 at 4 mA cm−2. This value is almost sixfold higher than that of the pristine Fe2O3 NWAs/CNTF electrode. When a cathode containing zinc-nickel-cobalt oxide (ZNCO)@Ni(OH)2 NWAs heterostructures is used, 0.46 mAh cm−2 capacity and 67.32 mWh cm−3 energy density are obtained for quasi-solid-state fiber-shaped NiCo-Fe batteries, which outperform most state-of-the-art fiber-shaped aqueous rechargeable batteries. These findings offer an innovative and feasible route to design high-performance Fe-based anodes and may inspire new development for the next-generation wearable Ni-Fe batteries. Ministry of Education (MOE) Nanyang Technological University National Research Foundation (NRF) This work was supported in part by the Singapore Ministry of Education Academic Research Fund Tier 2 (MOE2019-T2-2-127), the Singapore Ministry of Education Academic Research Fund Tier 1 (MOE2019-T1-001-103 and MOE2019-T1-001-111), and the Singapore National Research Foundation Competitive Research Program (NRF-CRP18-2017-02). This work was also supported in part by Nanyang Technological University. W.G. is grateful to the support from the Natural Science Foundation of Jiangsu Province (BK20190228) and Guangdong Basic and Applied Basic Research Foundation (2019A1515110859).

Although the tensile strength of carbon nanotubes inherited from the sp2 hexagonal carbon lattice is as high as 120 GPa, the state-of-the-art mechanical resistance of carbon nanotube fibers is below 10 GPa. Material imperfections embedded in the complex microstructures are responsible for this remarkable reduction across multiple length scales. In this study, we rationalize this multi-scale degradation of mechanical performance through theoretical analysis of the processing-microstructure-performance relationship for carbon nanotube fibers based on the experiment data, offering a simplified model that not only quantifies the breakdown of material strength at the nanotube, bundle, and fiber levels, respectively, but also provides practical advices to optimize the manufacturing processes for elevated mechanical performance.

A high-performance fiber-shaped integrated multifunctional sensing system was designed and fabricated based on flexible fiber-shaped supercapacitors (FFSCs) and humidity sensors. A facile and cost-effective method was proposed to grow three-dimensional MnO2 nanoballs (NBs)@Ni cone/carbon nanotube (CNT) film with a high specific capacitance of 609.06 mF cm−2 at a current density of 0.5 mA/cm2. In addition, asymmetric coaxial FFSCs (ACFFSCs) with a maximum operating voltage of 1.8 V were assembled by wrapping MnO2 NBs@Ni cone/CNT film on MoS2 nanosheet arrays/carbon nanotube fibers as the inner and outer electrodes of the ACFFSCs device, respectively, with poly(vinyl alcohol)/KOH as the gel electrolyte. The assembled ACFFSCs device embraces a high specific capacitance of 195.38 mF cm−2, and a superior areal energy density of 83.59 μWh cm−2. Moreover, the ACFFSCs device acts as the stable power supply for the coaxial fibrous humidity sensor, and the obtained flexible humidity sensing system possesses high sensitivity (2.483/%RH) in the detection of relative humidity (RH), with a fast response speed of 0.39 s.

A new type of ternary carbon nanotube fiber (CNF)/three-dimensional (3D) porous carbon nanotubes (CNTs)/polyaniline (PANI) electrodes with a double core-sheathed architecture composed of CNF/CNTs and CNTs/PANI was fabricated via low-potential electrophoretic deposition of CNTs and subsequent electrochemical polymerization of PANI on the CNF surface. The resulting all-solid-state supercapacitor possesses a high specific capacitance of 67.31 mF cm−2 at the current density of 0.5 mA cm−2 and only a loss as less as 10% of its initial specific capacitance after 5000 charge-discharge cycles. Furthermore, it is capable of withstanding different bending deformations, and can maintain 99.8% capacitance, even after experiencing the bending of 180° for 500 times, which manifests a significant application potential in the field of flexible electronic devices.

The tensile mechanical properties of carbon nanotube (CNT) fiber, which is a one-dimensional assembly of ultra-strong CNTs, are still far short of our expectations. This is mainly due to their high porosity and relatively weak intertube load transfer efficiency. Previous studies have demonstrated that the fiber strength can be enhanced by the infiltration of polymer chains into the fiber. In this work, polyvinyl alcohol (PVA) was pre-infiltrated into loosely packed CNT ribbons, and the composite ribbons were then densified into the fiber form. This enabled a homogeneous dispersion of polymer chains within the CNT fibers. To enhance the mechanical properties of the CNT/PVA composite fibers, isothermal crystallization and ultrasonic treatments were implemented to increase the crystallization of PVA in the ribbon, and the composite fibers were hot-stretched to improve the alignment of both CNTs and PVA chains within the fibers. It was found that the tensile strength and modulus of the final composite fiber were 210% and 193.6% higher than those of the pristine CNT fiber. The structural evolution during these treatments and the mechanism of fiber strengthening were systematically investigated.

High reflection loss, wide bandwidth and low density are desirable attributes of electromagnetic wave absorption materials. Here, an ultra-thin MnO2/Fe3O4/carbon nanotube film has been synthesized in two steps using solvothermal deposition and electrochemical deposition. The Fe3O4 nanoparticles and the MnO2 sheets form a nano-scale core-shell structure on the surface of the carbon nanotube film. A series of this hierarchical composite film with different shell structures and MnO2 weight ratios were successfully synthesized. Their unique micro-structure greatly enhances the electromagnetic wave absorption capability of the composites. Instrinsic ferromagnetism is confirmed by the magnetic hysteresis loops. The strong couplings among dielectric loss, hysteresis loss and multiple scattering resulted in the reflection loss up to −42.2 dB with the bandwidth of 7.1 GHz at 10% MnO2 weight ratio for a flexible composite film of 1 mm thick.

Graphite films have excellent in-plane thermal conductivity but extremely low through-thickness thermal conductivity because of their intrinsic inter-layer spaces. To improve the inter-layer heat transfer of graphite films, we developed a simple interfacial modification with a short duration mixed-acid treatment. The effects of the mixture ratio of sulfuric and nitric acids and treatment time on the through-thickness thermal properties of graphite films were studied. The modification increased the through-thickness thermal conductivity by 27% and 42% for the graphite film and its composite, respectively. X-ray photoelectron spectroscopy, X-ray powder diffraction, and scanning electron microscopy results indicated that the acidification process had two competing effects: the positive contribution made by the enhanced interaction between the graphite layers induced by the functional groups and the negative effect from the destruction of the graphite layers. As a result, an optimal acidification method was found to be sulfuric/nitric acid treatment with a mixture ratio of 3:1 for 15 min. The resultant through-thickness thermal conductivity of the graphite film could be improved to 0.674 W/mK, and the corresponding graphite/epoxy composite shows a through-thickness thermal conductivity of 0.587 W/mK. This method can be directly used for graphite films and their composite fabrication to improve through-thickness thermal conductivity.

Boron nitride nanosheets (BNNSs) are a structural analogue of graphene that are thought to exhibit good tribological performances, due to their typical laminated structure. However, the tribological properties of pure solid BNNSs have not been thoroughly researched, which may be resulted from the lack of knowledge regarding the synthesis of this special two-dimensional (2D) material. In this work, BNNSs were deposited on silicon wafers via nitridation of magnesium diboride (MgB 2 ) in a chemical vapor deposition system. The ammonia (NH 3 ) was used as the nitrogen source. The tribological behaviors of the synthesized BNNSs, including friction and wear resistance, were evaluated with a CSM tribometer. The results indicated that the BNNSs can decrease the friction of bare silicon wafer. The average value of the friction coefficients had no obvious change with the changes in load and frequency. The wear rate increased when the load and frequency increased. The results suggested that the BNNSs had good potential applications in industrial lubrication, after they were modified by small molecules or polymers.

Fiber-based supercapacitors (FSCs) are new members of the energy storage family. They present excellent flexibility and have promising applications in lightweight, flexible, and wearable devices. One of the existing challenges of FSCs is enhancing their energy density while retaining the flexibility. We developed a facile and cost-effective method to fabricate a highly capacitive positive electrode based on hierarchical ferric-cobalt-nickel ternary oxide nanowire arrays/graphene fibers and a negative electrode based on polyaniline-derived carbon nanorods/graphene fibers. The elegant microstructures and excellent electrochemical performances of both electrodes enabled us to construct a highperformance flexible asymmetric graphene fiber-based supercapacitor device with an operating voltage of 1.4 V, a specific capacitance up to 61.58 mF·cm–2, and an energy density reaching 16.76 μW·h·cm–2. Moreover, the optimal device presents an outstanding cycling stability with 87.5% initial capacitance retention after 8,000 cycles, and an excellent flexibility with a capacitance retention of 90.9% after 4,000 cycles of repetitive bending.

An integrated self-charging power system incorporating flexible fiber-shaped coaxial asymmetric supercapacitors (FASCs) with flexible triboelectric nanogenerators (FTENGs) has the potential to harvest and store energy simultaneously for achieving self-charged power pack. In this study, we develops a new strategy for fabricating a metal-organic framework (MOF) for the template-directed growth of hierarchically well-oriented nanowire arrays based on carbon nanotube fibers (CNTFs) for electrochemical supercapacitors. Uniform CNTFs@ZnCo2O4@Zn-Co-S hybrid arrays (HAs) derived from a zinc/cobalt-based zeolitic imidazolate framework (Zn/Co-ZIF) are first fabricated via a facile annealing and sulfuration process and a CNTFs@H-Co3O4@CoNC HA derived from a Co-based MOF is synthesized via oxidation and carbonization processes; the products act as positive and negative electrodes respectively in the assembled FASCs. The as-prepared CNTFs@ZnCo2O4@Zn-Co-S HAs and CNTFs@H-Co3O4@CoNC HAs are endowed with rich reaction sites, a facile ion diffusion path, and improved conductivity because of their unique hierarchical structure and good synergistic effect, which improves the electrochemical properties of the MOF derivatives. In addition, the assembled FASCs device exhibits a remarkable electrochemical performance with excellent rate capability. This study provides a strategy for the rational design of hierarchically structured, well-oriented MOFs and derivative arrays with high electrochemical performance and mechanical flexibility. Moreover, the flexible fiber-shaped MOF–derivative HA asymmetric supercapacitor is charged by a flexible triboelectric nanogenerator, demonstrating the promise of an self-charging power pack that has considerable potential for developing flexible multifunctional electronic devices.

Active control of nanocrystal optical and electrical properties is crucial for many of their applications. By electrochemical (de)lithiation of Cu2-xSe, a highly doped semiconductor, dynamic and reversible manipulation of its NIR plasmonics has been achieved. Spectroelectrochemistry results show that NIR plasmon red-shifted and reduced in intensity during lithiation, which can be reversed with perfect on-off switching over 100 cycles. Electrochemical impedance spectroscopy reveals that a Faradaic redox process during Cu2-xSe (de)lithiation is responsible for the optical modulation, rather than simple capacitive charging. XPS analysis identifies a reversible change in the redox state of selenide anion but not copper cation, consistent with DFT calculations. Our findings open up new possibilities for dynamical manipulation of vacancy-induced surface plasmon resonances and have important implications for their use in NIR optical switching and functional circuits.

To create high energy density fiber-shaped supercapacitors (FSCs), a new class of hierarchical electrodes with high electrical conductivity and good mechanical stability is needed. Here, a novel electrode consisting of porous manganese–nickel–cobalt sulfide (MNCS) multi-tripod nanotube arrays (NTAs) on carbon nanotube fibers (CNTFs) is prepared by a facile and cost-effective synthesis. The MNCS NTAs/CNTF electrode achieves a high specific capacitance of 2554.5 F cm−3, which is attributed to the high electrical conductivity and richer redox reactions of MNCS NTAs resulting from mixing three metal elements followed by sulfidation, and high porosity but a robust architecture. The unique features of these electrodes allowed us to successfully fabricate a fiber-shaped asymmetric supercapacitor (FASC) with a maximum operating voltage of 1.6 V by using the vanadium nitride (VN) nanowires (NWs) on CNTF electrode as the negative electrode. A volumetric capacitance of 147.3 F cm−3 and an energy density of 52.4 mW h cm−3 of the as-obtained FASC device are higher than those reported for similar devices. In addition, our FASC device possesses outstanding reliability and achieves a retaining capacitance of 92.9% after 5000 bending cycles. Thus, this work develops hierarchical, porous MNCS multi-tripod NTAs as a promising candidate for next-generation electrode materials with high electrochemical performance.

Solution spinning is the most promising approach of fabricating continuous carbon nanotube (CNT) fibers in industrial scale. Understanding the relationship between processing, structures and properties is of great significance for the optimization and application of solution spun CNT fibers. In this study, the influence of dispersion time on the microstructural and mechanical properties of CNT solutions and their spun fibers were systematically investigated. It has been found that with the increasing of dispersion time, CNT bundle size and length decreased, resulting in improved homogeneity of CNT dispersions, while the mechanical properties of CNT fibers increased firstly and then decreased. The orientation of CNTs along the fiber axis was found undesirable when CNTs were either too short or too long in the solution. This study provided a general guidance for fabricating high-performance fibers from one-dimensional nanomaterials .

In this study, the loading rate sensitivity of the mode II fracture behaviour of composites toughened by carbon nanotubes (CNTs) was investigated. CNTs were inserted into laminates in the form of films. The specimens for the mode II fracture test were subjected to loading rates varying from the quasi-static 8 × 10−6 m/s) to dynamic (15 m/s) states using an Instron machine and electromagnetic Hopkinson bar, respectively. Under the quasi-static loading conditions, the fracture toughness of the composites increased monotonously with an increase in the number of CNT layers and approached a maximum value when 30 layers of the CNT film were added, which is twice the value of the virgin specimen (without CNTs). However, under the dynamic loading conditions, the fracture toughness of the composites improved only by 25% compared with that of the virgin specimen, and the change in the number of CNT layers had little effect on the fracture toughness of the composites. This indicated that under dynamic loading, the failure mode of the interlaminar region changed. Microscope observation results illustrate that a large amount of in-plane (x-y plane) shear failure occurs in the CNT-interleaved zone under the dynamic loading conditions.

Boron nitride nanotubes (BNNTs) can be grown on stainless steel by annealing a mixture of diboron trioxide (B 2 O 3 ) and boron (B) at 1200–1300 °C under ammonia (NH 3 ). In previously reported boron oxide chemical vapor deposition methods for the synthesis of BNNTs, diboron dioxide (B 2 O 2 ) is generated in situ by the reaction of boron and metal oxides. In this study, we directly used a mixture of B 2 O 3 and boron as boron sources, thereby, avoiding the use of metal containing species in the starting material. The concentration of B 2 O 3 significantly influenced the formation, quality and quantity of BNNTs.

A high-performance, all-solid-state hybrid supercapacitor (HSC) device was assembled successfully. The ZnCo 2 O 4 nanowire array (NA)/carbon nanotube film (CNTF) positive electrode materials and the assembled device possess areal specific capacitances of 1.019 F cm −2 and 158.08 mF cm −2 , respectively. A supernal volume energy density of 49.5 mWh cm −3 was obtained when the voltage window increased to 1.5 V. Moreover, the assembled HSC device exhibited good cycling stability with 90.7% initial capacitance retention after 6000 cycles, and the coulombic efficiency remained near 100%.

In this study, we report a time- and energy-saving out-of-oven curing process based on the resistive heating of a macroscale carbon nanotube (CNT) film made using the floating catalyst chemical vapor deposition method. CNT film can be heated up very quickly when connected to an electrical power source. By coating CNT film onto the surface of uncured glass fiber reinforced polymer composites, the composites can be cured by the resistive heating of the CNT film. The degree of cure, loss storage, and tensile properties of the composites made from the new process are almost the same as those made from the traditional oven heating process. However, the new curing process is much faster, and its energy consumption is found to be only one seventh that of the oven curing process. The deicing of glass fiber composites based on the resistive heating of CNT film is also demonstrated.

Fiber-shaped asymmetric supercapacitors (FASCs) have attracted considerable attention due to their potential application in portable and wearable electronics. Although high stretchability have been achieved in fiber-shaped supercapacitors, low energy density severely restricts their practical applications. This study develops a simple and cost-effective method to synthesize highly capacitive hierarchically-structured MnO2@PEDOT:PSS@oxidized carbon nanotube fibers (MnO2@PEDOT:PSS@OCNTF) positive electrode and flower-like MoS2 nanosheets@CNTF (MoS2@CNTF) negative electrode. Their intriguing structural features allowed us to successfully fabricate a prototype stretchable FASC with a maximum operating voltage of 1.8 V. Due to the synergy of the MnO2@PEDOT:PSS@OCNTF and MoS2@CNTF, the optimized stretchable FASC device exhibits a remarkable specific capacitance of 278.6 mF/cm2 and a superior energy density of 125.37 μWh/cm2, which are higher than those of any reported state-of-the-art fiber-shaped supercapacitors. In addition, the device possesses outstanding stretchability, as it maintains a capacitance retention of 92% after stretching at a strain of 100% for 3000 cycles. These stretchable FASCs have great potential as power sources for next-generation portable and wearable electronics.

Fast growing flexible and wearable electronics and devices require thermal management materials having not only high thermal conductivity but also structural flexibility with mechanical robustness. However, most developed thermal management materials are relatively rigid and have low strength. Herein, we report a carbon nanotube/graphene hybrid film that combines high thermal conductivity (up to 1056 W/(mK)), extraordinary structural flexibility, and high mechanical strength (∼1 GPa). Such film consists of alternately stacked aligned, long and thin carbon nanotube sheets, which provide a mechanically strong and thermally conductive scaffold, and graphene sheets, which act as a highly conductive component. The hybrid film was prepared by in-situ spraying graphene oxide sheet solution onto an aligned, freestanding carbon nanotube aerogel sheet during winding the sheet on a rotating mandrel, followed by high-temperature annealing. Experimental and theoretical results suggested that the removal of defects of the hybrid films and the formation of covalent bonding between carbon nanotubes and graphene sheets resulted in improved thermal conductivities and mechanical strength. Application of such film as an orientational heat spreader has been demonstrated.

AbstarctGraphene has sparked extensive research interest for its excellent physical properties and its unique potential for application in absorption of electromagnetic waves. However, the processing of stable large-scale graphene and magnetic particles on a micrometer-thick conductive support is a formidable challenge for achieving high reflection loss and impedance matching between the absorber and free space. Herein, a novel and simple approach for the processing of a CNT film-Fe3O4-large scale graphene composite is studied. The Fe3O4 particles with size in the range of 20–200 nm are uniformly aligned along the axial direction of the CNTs. The composite exhibits exceptionally high wave absorption capacity even at a very low thickness. Minimum reflection loss of −44.7 dB and absorbing bandwidth of 4.7 GHz at −10 dB are achieved in composites with one-layer graphene in six-layer CNT film-Fe3O4 prepared from 0.04 M FeCl3. Microstructural and theoretical studies of the wave-absorbing mechanism reveal a unique Debye dipolar relaxation with an Eddy current effect in the absorbing bandwidth.

Integrating a plasmonic metal and a semiconductor at the nanoscale is of great importance for exploring their optical coupling properties. However, the synthesis and fine structural control of such nanostructures remain challenging. Herein we report the facile aqueous-phase Se-mediated overgrowth of metal selenides onto Au nanocrystals. Taking plasmonic Cu2–xSe as an example, the introduction of a Se template allows deposition of large Cu2–xSe crystalline grains onto Au nanocrystal seeds in various shapes, including spheres, rods, and plates. Moreover, the configuration of Au–Cu2–xSe hybrids can be tuned from core–shell to heterodimer structure by controlling the growth behavior of the Se template. Se overgrowth depends critically on the absorption strength of stabilizers on Au seeds: a strongly absorbing stabilizer inhibits isotropic overgrowth, which is in agreement with molecular dynamics simulations. The resultant Au–Cu2–xSe hybrid nanocrystals possess multiple surface plasmon resonance modes. Finally...

The growing demand on flexible all-solid-state supercapacitors has accelerated the need for fundamental understanding of their response to extreme thermal environment. In this study, supercapacitors based on freestanding films composed of randomly oriented carbon nanotubes and H 2 SO 4 -PVA gel electrolyte were fabricated. The effect of temperature on their electrochemical behaviors was systematically investigated by using cyclic voltammogram, impedance spectroscopy and galvanostatic charge-discharge measurements at temperatures between −5 °C and 55 °C. The results indicated that the capacitance of the supercapacitor was enhanced by the increase of operating temperature while the internal resistance was reduced by virtue of the acceleration of transportation/adsorption of electrolyte ions and surface modification of the electrode. For instance, when charged with the current density of 0.2 mA cm −2 , the capacitance increased by 24.3% from −5 °C to 25 °C, and by 32.6% from 25 °C to 55 °C. Operating temperatures at or below 25 °C were found to facilitate the charge-discharge reversibility and long-term cycle stability. It has also been concluded that supercapacitors based on H 2 SO 4 -PVA gel electrolyte were not suitable for long term use at temperatures higher than 40 °C due to the aging of electrolyte.