Free‐Standing Carbon Nanofibrous Films Prepared by a Fast Microwave‐Assisted Synthesis Process

Carbon nanofibrous (CNF) films are of great interest for various applications, e.g., as substrates for electrodes, sensors, or catalysts. Here, a fast microwave‐assisted synthesis is reported to fabricate square‐centimeter large free‐standing carbon nanofibrous films of approximately 10 μm thickness utilizing nickel‐based catalysts and ethanol as carbon source. The obtained CNF coatings exhibit a good stability and partial self‐delamination from the substrate is observed, which enables their easy detachment from the substrate without the need for further treatment. Scanning electron microscopy is applied to investigate the morphology of the films and to develop a growth model.     

From Fragility to Flexibility: Construction of Hydrogel Bridges toward a Flexible Multifunctional Free‐Standing CaCO3 Film

Free‐standing CaCO₃ materials are an important member in biological systems because of their existence in many natural organisms such as nacre, shell, and crustacean cuticle. However, toughness of those artificial mineral films is sacrificed once their inorganic content is up to 90%, thus free‐standing characteristics have seldom been achieved for CaCO₃ films, let alone their real applications. Herein a fast and simple method for constructing hydrogel “bridges” for CaCO₃ microparticles is presented, developing highly flexible free‐standing CaCO₃ films with only 5% organic content. Such integrated films have underwater superoleophobicity and self‐cleaning function, which guarantee their repeated application in oil/water separation. Furthermore, heavy metal ions can be efficiently removed by simple filtration with the films. Because of the self‐similar structure, the films are able to resist mechanical abrasion without losing the anti‐wetting property and separation efficiency. The free‐standing CaCO₃ films are put forward for the first time to practical application, demonstrating the strategy can bring a brilliant prospect to artificial biomineral materials.     

Free‐Standing Cell Sheet Assembled with Ultrathin Extracellular Matrix as an Innovative Approach for Biomimetic Tissues

Current artificial tissue‐substitutes have limited clinical applications due to unmatched complex combination of cells and extracellular matrix (ECM) as seen in native tissues. From a developmental perspective, the construction of effective biomimetic tissues is from the bottom (one‐dimensional nanoparticles or two‐dimensional membranes) up (three‐dimensional scaffolds or more complex composite). In a hierarchical architecture, each sub‐structure can be assembled in a flexible way with specific regulators and cells, which overcomes the deficiency of one‐for‐all scaffold. Here, a cell‐compatible cell‐lined layered nano‐membrane is developed. Bioactive molecules are mounted on a nano‐membrane and later released to its lined cell sheet. The cell‐lined membrane is in a free‐standing form to regulate cellular functions. The major advantage of this methodology is to provide a versatile approach to construct biomimetic tissues for clinical applications.     

Iron Fluoride–Carbon Nanocomposite Nanofibers as Free‐Standing Cathodes for High‐Energy Lithium Batteries

The development of low‐cost, high‐energy cathodes from nontoxic, broadly available resources is a big challenge for the next‐generation rechargeable lithium or lithium‐ion batteries. As a promising alternative to traditional intercalation‐type chemistries, conversion‐type metal fluorides offer much higher theoretical capacity and energy density than conventional cathodes. Unfortunately, these still suffer from irreversible structural degradation and rapid capacity fading upon cycling. To address these challenges, here a versatile and effective strategy is harnessed for the development of metal fluoride–carbon (C) nanocomposite nanofibers as flexible, free‐standing cathodes. By taking iron trifluoride (FeF₃) as a successful example, assembled FeF₃–C/Li cells with a high reversible FeF₃ capacity of 550 mAh g^?1 at 100 mA g^?1 (three times that of traditional cathodes, such as lithium cobalt oxide, lithium nickel cobalt aluminum oxide, and lithium nickel cobalt manganese oxide) and excellent stability (400+ cycles with little‐to‐no degradation) are demonstrated. The promising characteristics can be attributed to the nanoconfinement of FeF₃ nanoparticles, which minimizes the segregation of Fe and LiF upon cycling, the robustness of the electrically conductive C network and the prevention of undesirable reactions between the active material and the liquid electrolyte using the composite design and electrolyte selection.     

Self‐Organized Single‐Walled Carbon Nanotube Conducting Thin Films with Honeycomb Structures on Flexible Plastic Films

Complex 1, synthesized from anionic shortened single‐walled carbon nanotubes and cationic ammonium lipid dissolved in organic solvents, is cast on pretreated transparent flexible poly(ethylene terephthalate) (PET) films under a higher relative humidity to form thin films with self‐organized honeycomb structures. The cell sizes are controllable by changing the experimental conditions. The lipid, which is the cationic part of complex 1, is easily removed by a simple ion‐exchange method, while maintaining the basic honeycomb structures. After the ion exchange, the nanotube honeycomb films on PET with thinner skeletons exhibit a dramatic decrease in the surface resistivity from insulating to conducting. Carbon nanotubes with honeycomb structures formed by the self‐organization on flexible polymer films are useful in many areas of nanoscience and technology including nanomaterials, nanoelectronics, nanodevices, catalysts, sensors, and so on.     

Carbon Nanotubes on Polymeric Microcapsules: Free‐Standing Structures and Point‐Wise Laser Openings

Single‐wall carbon nanotubes modified by anionic polyelectrolyte molecules are embedded into the shells of microcapsules. Carbon nanotubes serve as rigid rods in a softer polymeric capsule, which forms a free‐standing shell upon treatment with glutaraldehyde and subsequent drying. The embedded carbon nanotubes exhibit a broad absorption in the UV–near‐infrared part of the spectrum, and that allows point‐wise activation and opening of the microcapsules by laser. Raman signal analysis shows changes of carbon‐nanotube‐specific lines after high‐power laser irradiation, which is characteristic of the formation of disordered carbonlike structures. These polyelectrolyte/carbon nanotube composite capsules represent a novel light‐addressable type of microcontainers.     

An Integrated Free‐Standing Flexible Electrode with Holey‐Structured 2D Bimetallic Phosphide Nanosheets for Sodium‐Ion Batteries

An integrated, free‐standing, and binder‐free type of flexible anode electrode is fabricated from numerous holey‐structured, 2D nickel‐based phosphide nanosheets connected with carbon nanotubes. This electrode architecture can not only uniformly disperse the nanosheets throughout the whole electrode to avoid aggregation or detachment, but also provide an ideal sodium ion and electrolyte diffusion and penetration network with high electronic conductivity. Meanwhile, bimetallic phosphide formation by introducing secondary metal species will lead to a synergistic effect to modify the electrochemical properties. Due to the excellent compositional and structural characteristics of this electrode, it delivers superior performance. This designed flexible anode with Ni_1.5Co_0.5P_x nanosheets demonstrates a reversible capacity of 496.4 mAh g^?1 at 0.5 C and a good rate capacity of 276.1 mAh g^?1 at 8 C. Meanwhile, this connected integrated network woven from carbon nanotubes can effectively restrain volumetric expansion and shrinkage, and affect the conversion reaction products formation as well, from large‐sized microspheres to film structure, which is primarily credited with the improvement in electrochemical performance. This work may open up a new path for the synthesis of morphology‐controlled phosphides and promote the further development of flexible devices.     

ITO‐Free and Flexible Organic Photovoltaic Device Based on High Transparent and Conductive Polyaniline/Carbon Nanotube Thin Films

The synthesis and characterization of thin films of polyaniline/carbon nanotubes nanocomposites is reported, as well as their utilization as transparent electrodes in ITO‐free organic photovoltaic devices. These films are generated by interfacial synthesis, which provides them with the unique ability to be deposited onto any substrate as transparent films, thus enabling the production of flexible solar cells using substrates like PET. Very high carbon nanotube loadings can be achieved using these films without significantly affecting their transparency (≈80–90% transmittance at 550 nm). Sheet resistances as low as 300 Ω/□ are obtained using secondary polyaniline doping in the presence of carbon nanotubes. These films present excellent mechanical stability, exhibiting no lack in performance after 100 bend cycles. Flexible and completely ITO‐free organic photovoltaic devices are built using these films as transparent electrodes, and high efficiencies (up to 2.27%) are achieved.     

A Controllable Self‐Assembly Method for Large‐Scale Synthesis of Graphene Sponges and Free‐Standing Graphene Films

A simple method to prepare large‐scale graphene sponges and free‐standing graphene films using a speed vacuum concentrator is presented. During the centrifugal evaporation process, the graphene oxide (GO) sheets in the aqueous suspension are assembled to generate network‐linked GO sponges or a series of multilayer GO films, depending on the temperature of a centrifugal vacuum chamber. While sponge‐like bulk GO materials (GO sponges) are produced at 40 °C, uniform free‐standing GO films of size up to 9 cm² are generated at 80 °C. The thickness of GO films can be controlled from 200 nm to 1 µm based on the concentration of the GO colloidal suspension and evaporation temperature. The synthesized GO films exhibit excellent transparency, typical fluorescent emission signal, and high flexibility with a smooth surface and condensed density. Reduced GO sponges and films with less than 5 wt% oxygen are produced through a thermal annealing process at 800 °C with H₂/Ar flow. The structural flexibility of the reduced GO sponges, which have a highly porous, interconnected, 3D network, as well as excellent electrochemical properties of the reduced GO film with respect to electrode kinetics for the [Fe(CN)₆]^3?/4? redox system, are demonstrated.     

Spin‐ and Spray‐Deposited Single‐Walled Carbon‐Nanotube Electrodes for Organic Solar Cells

Organic bulk‐heterojunction solar cells using thin‐film single‐walled carbon‐nanotube (SWCNT) anodes deposited on glass are reported. Two types of SWCNT films are investigated: spin‐coated films from dichloroethane (DCE), and spray‐coated films from deionized water using sodium dodecyl sulphate (SDS) or sodium dodecyl benzene sulphonate (SDBS) as the surfactant. All of the films are found to be mechanically robust, with no tendency to delaminate from the underlying substrate during handling. Acid treatment with HNO₃ yields high conductivities >1000 S cm^?1 for all of the films, with values of up to 7694 ± 800 S cm^?1 being obtained when using SDS as the surfactant. Sheet resistances of around 100 Ω sq^?1 are obtained at reasonable transmission, for example, 128 ± 2 Ω sq^?1 at 90% for DCE, 57 ± 3 Ω sq^?1 at 65% for H₂O:SDS, and 68 ± 5 Ω sq^?1 at 70% for H₂O:SDBS. Solar cells are fabricated by successively coating the SWCNT films with poly(3,4‐ethylenedioxythiophene):poly(styrene sulphonate) (PEDOT:PSS), a blend of regioregular poly(3‐hexylthiophene) (P3HT) and 1‐(3‐methoxy‐carbonyl)‐propyl‐1‐phenyl‐(6,6)C₆₁ (PCBM), and LiF/Al. The resultant devices have respective power conversions of 2.3, 2.2 and 1.2% for DCE, H₂O:SDS and H₂O:SDBS, with the first two being at a virtual parity with reference devices using ITO‐coated glass as the anode (2.3%).     

Charged Rod‐Like Nanoparticles Assisting Single‐Walled Carbon Nanotube Dispersion in Water

A new dispersant for stabilization of single wall carbon nanotubes (SWNTs) in water that simultaneously utilizes three different dispersion or stabilization mechanisms: surfactant adsorption, polymeric wrapping, and Coulomb repulsive interaction, has been demonstrated. The new dispersant, a charged rod‐like nanoparticle (cROD), is a cylindrical micelle wrapped by negatively charged polymers which is fabricated by the aqueous free radical polymerization of a polymerizable cationic surfactant, cetyltrimethylammonium 4‐vinylbenzoate (CTVB), in the presence of sodium 4‐styrenesulfonate (NaSS). The surface charge density of the cRODs is controlled by varying the concentration of NaSS. Dispersions of SWNTs are obtained by sonicating a mixture of SWNTs and cROD in water, followed by ultra‐centrifugation and decanting. While the cRODs with neutral or low surface change densities (0 and 5 mol % NaSS) result in very low dispersion power and poor stability, the cRODs with high surface charge densities (15, 25, and 40 mol % NaSS) produce excellent dispersions with SWNT concentration as high as 437 mg L^?1 and long term stability. The sharp van Hove transition peaks of the cROD assisted SWNT dispersions indicate the presence of individually isolated SWNTs. Atomic force microscopy and small angle neutron scattering analysis show that the dominant encapsulation structure of the cROD assisted SWNTs is surfactant assisted polymeric wrapping. SWNTs dispersed by the cRODs can be fully dried and easily re‐dispersed in water, providing enhanced processibility of SWNTs.     

Hierarchical Free‐Standing Carbon‐Nanotube Paper Electrodes with Ultrahigh Sulfur‐Loading for Lithium–Sulfur Batteries

The rational combination of conductive nanocarbon with sulfur leads to the formation of composite cathodes that can take full advantage of each building block; this is an effective way to construct cathode materials for lithium–sulfur (Li–S) batteries with high energy density. Generally, the areal sulfur‐loading amount is less than 2.0 mg cm^?2, resulting in a low areal capacity far below the acceptable value for practical applications. In this contribution, a hierarchical free‐standing carbon nanotube (CNT)‐S paper electrode with an ultrahigh sulfur‐loading of 6.3 mg cm^?2 is fabricated using a facile bottom–up strategy. In the CNT–S paper electrode, short multi‐walled CNTs are employed as the short‐range electrical conductive framework for sulfur accommodation, while the super‐long CNTs serve as both the long‐range conductive network and the intercrossed mechanical scaffold. An initial discharge capacity of 6.2 mA·h cm^?2 (995 mA·h g^?1), a 60% utilization of sulfur, and a slow cyclic fading rate of 0.20%/cycle within the initial 150 cycles at a low current density of 0.05 C are achieved. The areal capacity can be further increased to 15.1 mA·h cm^?2 by stacking three CNT–S paper electrodes—resulting in an areal sulfur‐loading of 17.3 mg cm^?2—for the cathode of a Li–S cell. The as‐obtained free‐standing paper electrode are of low cost and provide high energy density, making them promising for flexible electronic devices based on Li–S batteries.     

Electrochemical Properties of High‐Power Supercapacitors Using Single‐Walled Carbon Nanotube Electrodes

We have investigated the key factors determining the performance of supercapacitors constructed using single‐walled carbon nanotube (SWNT) electrodes. Several parameters, such as composition of the binder, annealing temperature, type of current collector, charging time, and discharging current density have been optimized for the best performance of the supercapacitor with respect to energy density and power density. We find a maximum specific capacitance of 180 F/g and a measured power density of 20 kW/kg at energy densities in the range from 7 to 6.5 Wh/kg at 0.9 V in a solution of 7.5 N KOH (the currently available supercapacitors have energy densities in the range 6–7 Wh/kg and power density in the range 0.2–5 kW/kg at 2.3 V in non‐aqueous solvents).     

Additive‐Free Dispersion of Single‐Walled Carbon Nanotubes and Its Application for Transparent Conductive Films

A good dispersion of single‐walled carbon nanotubes (SWCNTs) in liquid media is a prerequisite to fulfill many of their applications. This contribution reports an efficient approach to additive‐free dispersion of SWCNTs with the aid of functionalized carbonaceous byproducts (CBs, e.g., amorphous carbon, carbon nanoparticles, and carbonaceous fragments) in SWCNT products. SWCNT bundles are treated by oleum intercalation and nitric acid oxidation in sequence, which leads to the selective functionalization of the CBs while the structure and properties of the SWCNTs are well preserved. These functionalized CBs can improve the subsequent dispersion of SWCNTs and the majority of SWCNTs in the suspension are present in small bundles or individually. Moreover, SWCNT transparent conductive films (TCFs) are fabricated by using these suspensions. The SWCNT TCFs obtained can achieve a low sheet resistance of 76 and 133 Ω sq^?1, with optical transmittance of 82% and 90% at 550 nm, respectively.     

A Free‐Standing and Ultralong‐Life Lithium‐Selenium Battery Cathode Enabled by 3D Mesoporous Carbon/Graphene Hierarchical Architecture

High capacity cathode materials for long‐life rechargeable lithium batteries are urgently needed. Selenium cathode has recently attracted great research attention due to its comparable volumetric capacity to but much better electrical conductivity than widely studied sulfur cathode. However, selenium cathode faces similar issues as sulfur (i.e., shuttling of polyselenides, volumetric expansion) and high performance lithium‐selenium batteries (Li–Se) have not yet been demonstrated at selenium loading >60% in the electrode. In this work, a 3D mesoporous carbon nanoparticles and graphene hierarchical architecture to storage selenium as binder‐free cathode material (Se/MCN‐RGO) for high energy and long life Li–Se batteries is presented. Such architecture not only provides the electrode with excellent electrical and ionic conductivity, but also efficiently suppresses polyselenides shuttling and accommodates volume change during charge/discharge. At selenium content of 62% in the entire cathode, the free‐standing Se/MCN‐RGO exhibits high discharge capacity of 655 mAh g^?1 at 0.1 C (97% of theoretical capacity) and long cycling stability with a very small capacity decay of 0.008% per cycle over 1300 cycles at 1 C. The present report demonstrates significant progress in the development of high capacity cathode materials for long‐life Li batteries and flexible energy storage device.     

Emulsifier‐Free Graphene Dispersions with High Graphene Content for Printed Electronics and Freestanding Graphene Films

A novel and highly versatile synthetic route for the production of functionalized graphene dispersions in water, acetone, and isopropanol (IPA), which exhibit long‐term stability and are easy to scale up, is reported. Both graphene functionalization (wherein the oxygen content can be varied from 4 to 16 wt%) and dispersion are achieved by the thermal reduction of graphite oxide, followed by a high‐pressure homogenization (HPH) process. For the first time, binders, dispersing agents, and reducing agents are not required to produce either dilute or highly concentrated dispersions of single graphene sheets with a graphene content of up to 15 g L^?1. High graphene content is essential for the successful printing of graphene dispersions by 3D microextrusion. Free‐standing graphene films and micropatterned graphene materials are successfully prepared using this method. Due to the absence of toxic reducing agents, the graphene exhibits no cytotoxicity and is biocompatible. Furthermore, the electrical conductivity of graphene is significantly improved by the absence of binders. Flexible microarrays can be printed on different substrates, producing microarrays that are mechanically stable and can be bent several times without affecting electrical conductivity.     

Self‐Assembly of Flexible Free‐Standing 3D Porous MoS2‐Reduced Graphene Oxide Structure for High‐Performance Lithium‐Ion Batteries

Flexible freestanding electrodes are highly desired to realize wearable/flexible batteries as required for the design and production of flexible electronic devices. Here, the excellent electrochemical performance and inherent flexibility of atomically thin 2D MoS₂ along with the self‐assembly properties of liquid crystalline graphene oxide (LCGO) dispersion are exploited to fabricate a porous anode for high‐performance lithium ion batteries. Flexible, free‐standing MoS₂–reduced graphene oxide (MG) film with a 3D porous structure is fabricated via a facile spontaneous self‐assembly process and subsequent freeze‐drying. This is the first report of a one‐pot self‐assembly, gelation, and subsequent reduction of MoS₂/LCGO composite to form a flexible, high performance electrode for charge storage. The gelation process occurs directly in the mixed dispersion of MoS₂ and LCGO nanosheets at a low temperature (70 °C) and normal atmosphere (1 atm). The MG film with 75 wt% of MoS₂ exhibits a high reversible capacity of 800 mAh g^?1 at a current density of 100 mA g^?1. It also demonstrates excellent rate capability, and excellent cycling stability with no capacity drop over 500 charge/discharge cycles at a current density of 400 mA g^?1.