Design and Preparation of Flexible Graphene/Nonwoven Composites with Simultaneous Broadband Absorption and Stable Properties

As the world moves into the 21st century, the complex electromagnetic wave environment is receiving widespread attention due to its impact on human health, suggesting the critical importance of wearable absorbing materials. In this paper, graphene nonwoven (RGO/NW) composites were prepared by diffusely distributing graphene sheets in a polypropylene three-dimensional framework through Hummers' method. Moreover, based on the Jaumann structural material design concept, the RGO/NW composite was designed as a multilayer microwave absorber, with self-recovery capability. It achieves effective absorption (reflection loss of -10 dB) in the 2~18 GHz electromagnetic wave frequency domain, exhibiting a larger bandwidth than that reported in the literature for absorbers of equivalent thickness. In addition, the rationally designed three-layer sample has an electromagnetic wave absorption of over 97% (reflection loss of -15 dB) of the bandwidth over 14 GHz. In addition, due to the physical and chemical stability of graphene and the deformation recovery ability of nonwoven fabric, the absorber also shows good deformation recovery ability and stable absorption performance. This broadband absorption and extreme environmental adaptability make this flexible absorber promising for various applications, especially for personnel wearable devices.

Characterization of Phase Change Materials Fabricated with Cross-Linked Graphene Aerogels

3D porous graphene aerogel exhibits a high surface area which can hold plenty of pure phase change material (PCM) into the internal space. In order to maintain the flexibility of PCM without volume shrinkage under the external force, cross-linked graphene aerogel was prepared by the cysteamine vapor method. The cross-linked graphene aerogel had a high stress–strain durability and chemical stability for infiltrating PCM to produce a form-stable PCM composite. The latent heat of PCM is one of the elements to estimate the capacity of PCM thermal energy storage (TES) during the phase transition process. The cross-linked graphene aerogel-supported PCM composite showed a great TES to be utilized in thermal-to-electrical energy harvesting. The cross-linked graphene aerogel also had an excellent mechanical property of preventing damage at a high temperature.

Structure-dependent mechanical properties of self-folded two-dimensional nanomaterials

The design of self-folded two-dimensional nanomaterials (SF-2DNMs) has been proposed to greatly enhance the ductility of two-dimensional material assemblies. However, the dependences of the mechanical properties of SF-2DNMs on the folded geometries have not been fully clarified. In this paper, we develop a theoretical model to describe the mechanical properties of SF-2DNMs based on the shear-lag analysis. With this model, the load transfer behaviors in SF-2DNMs are demonstrated. The Young's modulus and tensile strength of SF-2DNMs are found to increase and then converge with the fold length, which agree well with the results of molecular dynamics simulations. Moreover, the phase diagrams of failure modes are obtained for SF-2DNMs and their stacked assemblies, providing design criteria for the geometries of SF-2DNMs. The structure-property relationship revealed in our study will provide useful guidelines for the structure design and property optimization of SF-2DNMs.

The implementation of graphene-based aerogel in the field of supercapacitor

Graphene and graphene-based hybrid materials have emerged as an outstanding supercapacitor electrode material primarily because of their excellent surface area, high electrical conductivity, and improved thermal, mechanical, electrochemical cycling stabilities. Graphene alone exhibits electric double layer capacitance (EDLC) with low energy density and high power density. The use of aerogels in a supercapacitor is a pragmatic approach due to its extraordinary properties like ultra-lightweight, high porosity and specific surface area. The aerogels encompass a high volume of pores which leads to easy soak by the electrolyte and fast charge-discharge process. Graphene aerogels assembled into three-dimensional (3D) architecture prevent there stacking of graphene sheets and maintain the high surface area and hence excellent cycling stability and rate capacitance. However, the energy density of graphene aerogels is limited due to EDLC type of charge storage mechanism. Consequently, 3D graphene aerogel coupled with pseudocapacitive materials such as transition metal oxides, metal hydroxides, conducting polymers, nitrides, chalcogenides show an efficient energy density and power density performance due to the presence of both types of charge storage mechanisms. This laconic review focuses on the design and development of graphene-based aerogel in the field of the supercapacitor. This review is an erudite article about methods, technology and electrochemical properties of graphene aerogel.

In Situ Interface Design in Graphene-Embedded Polymeric Silica Aerogel with Organic/Inorganic Hybridization

For many practical applications, the most important factor is to have an improved interface between the matrix and dispersed phase in a compressible composite aerogel having a high degree of porosity and a large surface area. Although some measure of compressibility is obtained in polymer-based aerogels with a continuous backbone through the hybridization of the stiff backbone [polyvinyltrimethoxysilane (P-VTMS), -C-C-] and flexible backbone [poly(3-glycidyloxypropyl)trimethoxysilane (P-GPTMS), -C-O-C-], it seems that the extent of improvement is insignificant in terms of interface improvement, surface area increase, and ordered mesoporous network. In this study, the effects of the incorporation of graphene nanoplatelets (GnPs) on aerogels made of a backbone consisting of -C-O-C- (flexible backbone) were examined in terms of structural improvement and were compared with aerogels made of a backbone consisting of -C-C- (stiff backbone). Moreover, the inorganic siloxane cross-link density between the underlying polymer chains was controlled by inducing hydrogen bonding between polymer chains and GnPs. This approach reduces the structural shrinkage during gelation and drying. The integration of only 1 wt % GnP integrated into the backbone by using spinodal decomposition phase separation processing allowed control of the pore size and the surface area. Integration of GnPs through in situ exfoliation during sol-gel transition is shown to be the best approach using the lowest possible amount of GnPs to improve aerogels' mesoporous network made from polymerized GPTMS. A flexible backbone such as P-GPTMS chains is supposed to result in a compliant aerogel, but the chains tend to shrink extensively during gelation and drying, reducing the porosity. P-GPTMS-derived aerogel suffers from a wrong combination of flexible backbone conjugated with an extensive number of permanent chemical cross-links and abundant remaining unreacted hydroxyl groups that undergo permanent chemical shrinkage. To counteract this, the GnP-reinforced prepolymer precursor (P-GPTMS) with fewer siloxane cross-links was synthesized and studied. By use of this strategy, the same elastic properties as those seen with the hybrid P-VTMS- and hybrid P-GPTMS-derived aerogels were imparted, while also improving the mechanical strength by up to 138% and the surface area by up to 205% by controlling the extent of GnP exfoliation during the sol-gel transition. This exceptional effect of GnP on the surface area improvement was shown to be of up to 2.05-fold for P-GPTMS and 2.63-fold for P-VTMS material.

Development and Applications of MOFs Derivative One-Dimensional Nanofibers via Electrospinning: A Mini-Review

Metal organic frameworks (MOFs) have been exploited for various applications in science and engineering due to the possibility of forming different mesoscopic frameworks and pore structures. To date, further development of MOFs for practical applications in areas such as energy storage and conversion have encountered tremendous challenge owing to the unitary porous structure (almost filled entirely with micropores) and conventional morphology (e.g., sphere, polyhedron, and rod shape). More recently, one-dimensional (1D) MOFs/nanofibers composites emerged as a new molecular system with highly engineered novel structures for tailored applications. In this mini-review, the recent progress in the development of MOFs-based 1D nanofibers via electrospinning will be elaborated. In particular, the promising applications and underlying molecular mechanism of electrospun MOF-derived carbon nanofibers are primarily focused and analyzed here. This review is instrumental in providing certain guiding principles for the preparation and structural analysis of MOFs/electrospun nanofibers (M-NFs) composites and electrospun MOF-derived nanomaterials.

Modifying Reduced Graphene Oxide by Conducting Polymer Through a Hydrothermal Polymerization Method and its Application as Energy Storage Electrodes

We report chemical in situ deposition of conducting polymer poly (3,4-ethylenedioxythiophene) (PEDOT) on reduced graphene oxide (rGO) nanosheets through a simple hydrothermal polymerization method. The functional groups on graphene oxide (GO) were directly employed as an oxidant to trigger the polymerization of 3,4-ethylenedioxythiophene (EDOT), and the GO nanosheets were reduced into rGO accordingly in an aqueous environment. Well anchoring of ultrathin PEDOT on rGO through this oxidant-free method was confirmed by UV-Vis spectrum, FT-IR spectrum, SEM, and TEM analysis. The obvious enhancement of conductivity was observed after the covering of PEDOT on rGO, and this composite showed high conductivity about 88.5 S/cm. The electrochemical performance results revealed that rGO/PEDOT composite electrode exhibits high specific capacitance about 202.7 F/g. The good synergetic effect between PEDOT and rGO also makes sure highly stable reversibility of composite electrode during charging/discharging process, and more than 90% initial capacitance retains after 9000 times cycles. In addition, the electrode based on rGO/PEDOT deposited on the cotton fabric shows excellent flexible ability with the evidence that 98% of the initial capacitance of electrode maintained after three thousands of free bending, which shows promising energy storage performance for flexible devices. .

Facile One-Pot Synthesis of Bimetallic Co/Mn-MOFs@Rice Husks, and its Carbonization for Supercapacitor Electrodes

Novel hybrid nanomaterials comprising metal-organic framework compounds carbonised in the presence of biomass material derived from rice husk have been investigated as a new class of sustainable supercapacitor materials for electrochemical energy storage. Specifically, two synthetic routes were employed to grow Co/Mn metal-organic framework compounds in the channels of rice husks, which had been activated previously by heat treatment in air at 400 °C to produce a highly porous network. Pyrolysis of these hybrid materials under nitrogen at 700 °C for 6 h produced metal-containing phases within the nanocarbon, comprising intimate mixtures of Co, MnO and CoMn₂O₄. The materials thus produced are characterized in detail using a range of physical methods including XRD, electron microscopy and X-ray photoelectron spectroscopy. The synthetic pathway to the metal-organic framework compound is shown to influence significantly the physical properties of the resulting material. Electrochemical evaluation of the materials fabricated revealed that higher specific capacitances were obtained when smaller crystallite sized bimetallic Co/Mn-MOFs were grown inside the rice husks channels compared to larger crystallite sizes. This was in-part due to increased metal oxide loading into the rice husk owing to the smaller crystallite size as well as the increased pseudocapacitance exhibited by the smaller crystallite sizes and increased porosity.

Towards establishing standard performance metrics for batteries, supercapacitors and beyond

Electrochemical energy storage (EES) materials and devices should be evaluated against clear and rigorous metrics to realize the true promises as well as the limitations of these fast-moving technologies.

Recent Advances in 3D Graphene Architectures and Their Composites for Energy Storage Applications

Graphene is widely applied as an electrode material in energy storage fields. However, the strong π-π interaction between graphene layers and the stacking issues lead to a great loss of electrochemically active surface area, damaging the performance of graphene electrodes. Developing 3D graphene architectures that are constructed of graphene sheet subunits is an effective strategy to solve this problem. The graphene architectures can be directly utilized as binder-free electrodes for energy storage devices. Furthermore, they can be used as a matrix to support active materials and further improve their electrochemical performance. Here, recent advances in synthesizing 3D graphene architectures and their composites as well as their application in different energy storage devices, including various battery systems and supercapacitors are reviewed. In addition, their challenges for application at the current stage are discussed and future development prospects are indicated.

Perspective to the Potential Use of Graphene in Li-Ion Battery and Supercapacitor

Graphene is a hot star in materials science with various potential application aspects, including in Li-ion battery and supercapacitor. The burst of scientific papers in this area seems to validate the performance of graphene, but also arouses large dispute. Herein, we share our judgment of these trends to all, encouraging the discussion and enhancing the understanding of the structure-performance relationship of graphene.

Nitrogen-doped graphitic hierarchically porous carbon nanofibers obtained via bimetallic-coordination organic framework modification and their application in supercapacitors

Herein, N-doped graphitic hierarchically porous carbon nanofibers (NGHPCF) were prepared by electrospinning the composite of bimetallic-coordination metal-organic frameworks and polyacrylonitrile, followed by a pyrolysis and acid wash process. Control over the N content, specific surface area, and degree of graphitization of NGHPCF materials has been realized by adjusting the Co/Zn metal coordination content as well as the pyrolysis temperature. The obtained NGHPCF with a high specific surface area (623 m2 g-1) and nitrogen content (13.83 wt%) exhibit a high capacitance of 326 F g-1 at 0.5 A g-1. In addition, the capacitance of 170 F g-1 is still maintained at a high current density (40 A g-1); this indicates a high capacitance retention capability. Furthermore, a superb energy density (9.61 W h kg-1) is obtained with a high power density (62.4 W kg-1) using an organic electrolyte. These results fully illustrate that the prepared NGHPCF binder-free electrodes are promising candidates for high-performance supercapacitors.

Introducing catalytic gasification into chemical activation for the conversion of natural coal into hierarchically porous carbons with broadened pore size for enhanced supercapacitive utilization

A catalytic gasification mechanism is introduced to prepare natural coal derived hierarchically porous carbon exhibiting excellent supercapacitive performances.

Constructing Three-Dimensional Honeycombed Graphene/Silicon Skeletons for High-Performance Li-Ion Batteries

Silicon has been considered to be an attractive high-capacity anode material for next-generation lithium-ion batteries (LIBs). Currently, the commercial application of Si-based anodes is still restricted by its limited cycle life and rate capacity, which could be ascribed to the colossal volumetric change during the cycling process and poor electronic conductivity. We report the design of a unique Si-based nanocomposite of three-dimensional (3D) honeycombed graphene aerogel and the reduced graphene oxide sheets preprotected silicon secondary particles (SiNPs@rGO1). Through simple electrostatic self-assembly and hydrothermal processes, SiNPs are able to be wrapped with rGO1 to form reunited SiNPs@rGO1, and embedded into the backbone of 3D graphene honeycomb (rGO2). Such an intriguing design (namely, SiNPs@rGO1/rGO2) not only provides a conductive skeleton to improve the electrical conductivity, but also possesses abundant void spaces to accommodate the dramatic volume changes of SiNPs. Meanwhile, the outer rGO1 coats protect the inner SiNPs away from the electrolyte and prevent the destruction of the solid electrolyte interphase (SEI) film. As a result, the 3D honeycombed architecture achieves a high cyclability and excellent rate capability.

Highly Oriented Graphene Sponge Electrode for Ultra High Energy Density Lithium Ion Hybrid Capacitors

Highly oriented rGO sponge (HOG) can be easily synthesized as an effective anode for application in high-capacity lithium ion hybrid capacitors. X-ray diffraction and morphological analyses show that successfully exfoliated rGO sponge on average consists of 4.2 graphene sheets, maintaining its three-dimensional structure with highly oriented morphology even after the thermal reduction procedure. Lithium-ion hybrid capacitors (LIC) are fabricated in this study based on a unique cell configuration which completely eliminates the predoping process of lithium ions. The full-cell LIC consisting of AC/HOG-Li configuration has resulted in remarkably high energy densities of 231.7 and 131.9 Wh kg(-1) obtained at 57 W kg(-1) and 2.8 kW kg(-1). This excellent performance is attributed to the lithium ion diffusivity related to the intercalation reaction of AC/HOG-Li which is 3.6 times higher that of AC/CG-Li. This unique cell design and configuration of LIC presented in this study using HOG as an effective anode is an unprecedented example of performance enhancement and improved energy density of LIC through successful increase in cell operation voltage window.

Cartilage-inspired superelastic ultradurable graphene aerogels prepared by the selective gluing of intersheet joints

In this study, we demonstrate a cartilage-inspired superelastic and ultradurable nanocomposite strategy for the selective inclusion of viscoelastic poly(dimethylsiloxane) (PDMS) into graphene sheet junctions to create effective stress-transfer pathways within three-dimensional (3D) graphene aerogels (GAs). Inspired by the joint architectures in the human body, where small amounts of soft cartilage connect stiff (or hard) but hollow (and thus lightweight) bones, the 3D internetworked GA@PDMS achieves synergistic toughening. The resulting GA@PDMS nanocomposites exhibit fully reversible structural deformations (99.8% recovery even at a 90% compressive strain) and high compressive mechanical strength (448.2 kPa at a compressive strain of 90%) at repeated compression cycles. Owing to the combination of excellent mechanical and electrical properties, the GA@PDMS nanocomposites are used as signal transducers for strain sensors, showing very short response and recovery times (in the millisecond range) with reliable sensitivity and extreme durability. Furthermore, the proposed system is applied to electronic scales with a large detectable weight of about 4600 times greater than its own weight. Such bio-inspired cartilage architecture opens the door to fabricate new 3D multifunctional and mechanically durable nanocomposites for emerging applications, which include sensors, actuators, and flexible devices.

Toward highly compressible graphene aerogels of enhanced mechanical performance with polymer

The highly compressive durable graphene aerogels with enhanced strength was prepared by combining the freeze-casting process with the binding effect of polymer.

Activated mesoporous carbon nanofibers fabricated using water etching-assisted templating for high-performance electrochemical capacitors

Activated mesoporous carbon nanofibers are synthesized by a sequential process of electrospinning, water etching-assisted templating, and acid treatment, which exhibit outstanding capacitive performance.

One-pot synthesis of graphene/zinc oxide by microwave irradiation with enhanced supercapacitor performance

A facile one-step microwave irradiation method is developed to synthesize a composite of graphene and zinc oxide, which is quick and environmentally friendly.