Preparation of sulfur-doped graphene fibers and their application in flexible fibriform micro-supercapacitors

A novel type of sulfur-doped graphene fibers (S-GFs) were prepared by the hydrothermal strategy, the in situ interfacial polymerization method and the annealing method. Two S-GFs were assembled into an all-solid-state fibriform micro-supercapacitor (micro-SC) that is flexible and has a high specific capacitance (4.55 mF·cm^-2) with the current density of 25.47 pA·cm^-2. The cyclic voltammetry (CV) curve of this micro-SC kept the rectangular shape well even when the scan rate reached 2 V·s^-1. There is a great potential for this type of S-GFs used in flexible wearable electronics.     

Improved conductivity and capacitance of interdigital carbon microelectrodes through integration with carbon nanotubes for micro-supercapacitors

In the last decade,pyrolyzed-carbon-based composites have attracted much attention for their applications in micro-supercapacitors.Although various methods have been investigated to improve the performance of pyrolyzed carbons,such as conductivity,energy storage density and cycling performance,effective methods for the integration and mass-production of pyrolyzed-carbonbased composites on a large scale are lacking.Here,we report the development of an optimized photolithographic technique for the fine micropatterning of photoresist/chitosan-coated carbon nanotube (CHIT-CNT) composite.After subsequent pyrolysis,the fabricated carbon/CHIT-CNT microelectrode-based micro-supercapacitor has a high capacitance (6.09 mF.cm-2) and energy density (4.5 mWh.cm-3) at a scan rate of 10 mV.s-1.Additionally,the micro-supercapacitor has a remarkable long-term cyclability,with 99.9％ capacitance retention after 10,000 cyclic voltammetry cycles.This design and microfabrication process allow the application of carbon microelectromechanical system (C-MEMS)-based micro-supercapacitors due to their high potential for enhancing the mechanical and electrochemical performance of micro-supercapacitors.     

Carbon‐Nanomaterial‐Based Flexible Batteries for Wearable Electronics

Wearable electronics have received considerable attention in recent years. These devices have penetrated every aspect of our daily lives and stimulated interest in futuristic electronics. Thus, flexible batteries that can be bent or folded are desperately needed, and their electrochemical functions should be maintained stably under the deformation states, given the increasing demands for wearable electronics. Carbon nanomaterials, such as carbon nanotubes, graphene, and/or their composites, as flexible materials exhibit excellent properties that make them suitable for use in flexible batteries. Herein, the most recent progress on flexible batteries using carbon nanomaterials is discussed from the viewpoint of materials fabrication, structure design, and property optimization. Based on the current progress, the existing advantages, challenges, and prospects are outlined and highlighted.     

Flexible field emission of nitrogen-doped carbon nanotubes/reduced graphene hybrid films

The outstanding flexible field emission properties of carbon hybrid films made of vertically aligned N-doped carbon nanotubes grown on mechanically compliant reduced graphene films are demonstrated. The bottom-reduced graphene film substrate enables the conformal coating of the hybrid film on flexible device geometry and ensures robust mechanical and electrical contact even in a highly deformed state. The field emission properties are precisely examined in terms of the control of the bending radius, the N-doping level, and the length or wall-number of the carbon nanotubes and analyzed with electric field simulations. This high-performance flexible carbon field emitter is potentially useful for diverse, flexible field emission devices.     

Graphene-carbon nanotube hybrid films for high-performance flexible photodetectors

Graphene is being actively explored as a candidate material for flexible and stretchable devices.However,the development of graphene-based flexible photonic devices,i.e.photodetectors,is hindered by the low absorbance of the single layer of carbon atoms.Recently,van der Waals bonded carbon nanotube and graphene hybrid films have demonstrated excellent photoresponsivity,and the use of vein-like carbon nanotube networks resulted in significantly higher mechanical strength.Here,we report for the first time,a flexible photodetector with a high photoresponsivity of ～ 51 A/W and a fast response time of ～ 40 ms over the visible range,revealing the unique potential of this emerging all-carbon hybrid films for flexible devices.In addition,the device exhibits good robustness against repetitive bending,suggesting its applicability in large-area matrix-array flexible photodetectors.     

Frequency analysis of sandwich beam with FG carbon nanotubes face sheets and flexible core using high-order element

In the present paper, the vibrational behavior of sandwich beam with a flexible core and anti-symmetric functionally graded carbon nanotubes face sheet is investigated. Carbon nanotubes are considered as functional graded materials in the thickness of the faces and their properties change along the thickness of the face sheets. For the modeling of sandwich beam behavior, the Euler–Bernoulli theory is used for face sheets and the semi-3D elasticity is used for the core, which allowed us to investigate the flexibility of the core. Differential equations of motions are derived using the virtual displacement principle. In this research, a high-order element is presented for solving equations of motion, and then by using this element, the finite element formulation has been extracted and solved. Numerical results are obtained for various boundary conditions, which include simply support, clamped, free-clamped, and simply support-clamped. Also, different volumes of carbon nanotubes have been investigated for different distributions. The results showed that the distribution of the FG-X pattern carbon nanotube leads to the highest natural frequency of the beam. The main conclusion of this research is that, in most cases the FG-O pattern has the lowest natural frequencies and in some cases the FG-Λ pattern has the lowest natural frequencies. In other words, generally, it can be say that the lowest natural frequencies of the sandwich beam with functionally graded carbon nanotubes faces depend on the boundary conditions, thickness ratio, and also the volume fraction of carbon nanotubes. In this paper also the effect of geometric angles of the beam, such as the thickness of the core and face sheet thickness on natural frequency of the system is also investigated.     

Triboelectricity-assisted transfer of graphene for flexible optoelectronic applications

In this work, we developed a novel triboelectricity-assisted polymer-free method for the transfer of large-area chemical vapor deposited graphene films. With the assistance of electrostatic forces from friction-generated charges, graphene sheets were successfully transferred from copper foils to flexible polymer substrates. Characterization results confirmed the presence of high quality graphene with less defects and contaminations, compared to graphene transferred by conventional poly(methyl methacrylate)-mediated processes. In addition, the graphene samples possessed outstanding electrical transport capabilities and mechanical stability, when studied as electron transfer matrixes in graphene/ZnO hybrid flexible photodetectors. Our results showed a broad application potential for this transfer method in future flexible electronics and optoelectronics.

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计及变形耦合项的平面柔性梁动力学建模及频率分析

考虑了变形产生的几何非线性效应对作大范围运动的平面柔性梁的影响，在其纵向、横向的变形位移中均考虑了变形的二次耦合变量，从非线性应变-变形位移的原理出发，说明增加耦合变量后。使得剪应变近似为零，由此得出的变形模式更符合工程实际和简化需要。考虑两个方向的变形耦合后，采用有限元离散，通过Lagrange方程导出系统的动力学方程。最后对一作旋转运动的平面柔性梁进行仿真计算，并对其固有频率进行分析研究。将本文模型所得的结论。与一次耦合动力学模型、零次近似模型进行比较，说明了三种模型的差异。得到了作旋转运动的平面柔性梁的一些新特点。     

Synthesis of a Pillared Graphene Nanostructure: A Counterpart of Three‐Dimensional Carbon Architectures

Graphene is a single sheet of carbon atoms with outstanding electrical and physical properties and is being exploited for applications in electronics, sensors, photovoltaics, and energy storage. A novel 3D architecture called a pillared graphene nanostructure (PGN) is a combination of two allotropes of carbon, including graphene and carbon nanotubes. A one‐step chemical vapor deposition process for large‐area PGN fabrication via a combination of surface catalysis and in situ vapor–liquid–solid mechanisms is described. A process by which PGN layers can be transferred onto arbitrary substrates while keeping the 3D architecture intact is also described. Single and multilayer stacked PGNs are envisioned for future ultralarge and tunable surface‐area applications in hydrogen storage and supercapacitors.     

The Regulating Role of Carbon Nanotubes and Graphene in Lithium‐Ion and Lithium–Sulfur Batteries

The ever‐increasing demands for batteries with high energy densities to power the portable electronics with increased power consumption and to advance vehicle electrification and grid energy storage have propelled lithium battery technology to a position of tremendous importance. Carbon nanotubes (CNTs) and graphene, known with many appealing properties, are investigated intensely for improving the performance of lithium‐ion (Li‐ion) and lithium–sulfur (Li–S) batteries. However, a general and objective understanding of their actual role in Li‐ion and Li–S batteries is lacking. It is recognized that CNTs and graphene are not appropriate active lithium storage materials, but are more like a regulator: they do not electrochemically react with lithium ions and electrons, but serve to regulate the lithium storage behavior of a specific electroactive material and increase the range of applications of a lithium battery. First, metrics for the evaluation of lithium batteries are discussed, based on which the regulating role of CNTs and graphene in Li‐ion and Li–S batteries is comprehensively considered from fundamental electrochemical reactions to electrode structure and integral cell design. Finally, perspectives on how CNTs and graphene can further contribute to the development of lithium batteries are presented.     

Interactions and Chemical Transformations of Coronene Inside and Outside Carbon Nanotubes

By exposing flat and curved carbon surfaces to coronene, a variety of van der Waals hybrid heterostructures are prepared, including coronene encapsulated in carbon nanotubes, and coronene and dicoronylene adsorbed on nanotubes or graphite via π–π interactions. The structure of the final product is determined by the temperature of the experiment and the curvature of the carbon surface. While at temperatures below and close to the sublimation point of coronene, nanotubes with suitable diameters are filled with single coronene molecules, at higher temperatures additional dimerization and oligomerization of coronene occurs on the surface of carbon nanotubes. The fact that dicoronylene and possible higher oligomers are formed at lower temperatures than expected for vapor‐phase polymerization indicates the active role of the carbon surface used primarily as template. Removal of adsorbed species from the nanotube surface is of utmost importance for reliable characterization of encapsulated molecules: it is demonstrated that the green fluorescence attributed previously to encapsulated coronene is instead caused by dicoronylene adsorbed on the surface which can be solubilized and removed using surfactants. After removing most of the adsorbed layer, a combination of Raman spectroscopy and transmission electron microscopy was employed to follow the transformation dynamics of coronene molecules inside nanotubes.