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Hexagonal BCN (h-BCN) has been identified as a promising class of electromagnetic wave (EMW) absorption material for critical Mach number aerocraft due to its exceptional thermal and chemical stabilities as well as adjustable dielectric property. Herein, we report a facile precursor synthesis-pyrolysis method to obtain ultra-light h-BCN bulk ceramics and microtubes (MTs) using commercially available BCl3, ethylenediamine and aniline as the monomers. The h-BCN bulk with a density of 15 mg/cm3 can be in situ synthesized derived from the precursor located in a tube furnace, while h-BCN MTs are simultaneously obtained on the downstream graphite sheets by controlling the pyrolysis temperature at the wide range of 800–1200 °C. For the h-BCN bulk ceramics, the minimum reflection loss (RL) can be tailored by controlling the N dopants, ranging from −52.7 dB at 5.44 GHz (the band width below −10 dB is achieved in a wide frequency range from 2.8 to 18 GHz) to −20.6 dB at 14.8 GHz (the band width below −10 dB is narrowed from 13.4 to 18 GHz). The excellent and frequency-controllable microwave absorption properties are due to the combination of tunable complex permittivity and lattice polarization resulting from B and N dopants in carbon networks.

A novel method for producing graphene via enhanced shear exfoliation in a high-pressure fluid has been developed. In the process of exfoliation, graphite flakes, dispersed in a solution of N-methyl-2-pyrrolidone (NMP), were pushed through the exfoliation tube by a high-pressure pump, which produces high shear stresses on the graphite flakes due to the turbulent flow, causing the peeling-off of graphene sheets from the graphite flake. Atomic force microscopy (AFM) and transmission electron microscopy (TEM) images show that produced graphene sheets have thicknesses ranging from monolayer to about 12 layers. The results of X-ray photoelectron spectroscopy (XPS) and Raman and infrared (IR) spectroscopy analyses reveal that neither basal-plane defects nor oxides were noticeably introduced to graphene sheets in the process. The graphite solution can be continuously treated in a circular loop. At a pressure of 100 MPa and after 2 h of treatment, exfoliated graphene was obtained with a yield of about 15 ± 0.3%. T...

Carbon nanotubes (CNTs) are an effective spacer to prevent the re-stacking of graphene layers. However, the aggregation of CNTs always reduces the specific surface area of resulting CNT/graphene composites. Meanwhile, different pores always have different contributions to the specific capacitance. In this study, CNT/graphene composites with different porous structures are synthesized by co-reduction of oxidized CNTs and graphene oxide with different mixing ratios. With an optimized CNT content of 20%, the CNT/graphene composite shows 206 F g−1 in 1-ethyl-3-methylimidazolium tetrafluoroborate electrolyte. It is found that pores larger than twice the size of electrolyte ions can make greater contributions to the specific capacitance.

Unequal electrode capacitance in a symmetric supercapacitor results in an unequal voltage distribution on the two electrodes and the supercapacitor usually cannot utilize the full electrochemical window of electrolyte. In this study, the voltage distribution on the two electrodes of graphene supercapacitor is optimized by an adjustment of electrode mass ratio from 1 to 1.5 and an enlarged energy density of 118 Wh kg−1 is achieved at operating voltage 4.7 V using an ionic liquid electrolyte 1-methyl-1-propylpiperidinium bis (trifluoromethyl sulfonyl) imide (MPPp-TFSI).

The resolution of the electron microscope is now largely limited by the performance of its electron source when various aberrations in the electron imaging system, especially spherical aberrations, are corrected. A nanowire tip could be an ideal point electron source, where electrons are emitted from a small physical area. In this article, we review recent advances in electric-field-induced electron emission using a single nanowire, specifically, single-crystalline lanthanum hexaboride (LaB6) nanowire, compared to the state-of-the-art contemporary tungsten cold-field electron emitter W(310) as well as single atom tip and single-carbon nanotube emitters. Owing to its low work function, improved emission stability, and high emission brightness, the LaB6 nanowire as a cold-field-emission electron source offers a new and exciting opportunity for developing the next generation of electron microscopes.

We report an eco-friendly route for the reduction of graphene oxide (GO) by Azotobacter chroococcum at room temperature. Examinations using X-ray photoelectron spectroscopy, X-ray diffraction, and transmission electron microscopy indicate the formation of reduced graphene oxide (rGO) with a low degree of agglomeration. Quantitative analyses of electron diffraction data show that the produced rGO consists of single-layer sheets with a random stacking. It is suggested that the GO was reduced directly by the nitrogenase via sequential additions of electrons and protons followed by dehydration. This approach avoids the use of toxic chemical agents and also reduces the agglomeration of rGO.

Mn-Based compounds with high reversible capacities and eco-friendliness are one of the most promising anode materials for lithium ion batteries (LIBs), but their practical applications are still hindered by low rate capability, poor cycling stability, and high cost of production. Herein, we synthesize MnCO3/Mn3O4/reduced graphene oxide (MnCO3/Mn3O4/RGO) ternary composites through a green and facile strategy, which can take full advantage of the raw materials, mitigate pollution effectively, simplify the operating procedure, and shorten the preparation time to realize large-scale preparation. When used as anode materials for LIBs, benefitting from the advantage of their structure and effective synergy among MnCO3, Mn3O4 and graphene, the ternary composites exhibit an excellent cycling stability of 988 mA h g−1 after 200 cycles at 100 mA g−1 and 532 mA h g−1 after 800 cycles at 1 A g−1, which is superior to those of binary MnCO3/RGO and Mn3O4/RGO composites. Analyses using cyclic voltammetry, charge/discharge profiles, and electrochemical impedance spectroscopy reveal improved kinetics in the electrochemical reaction of the MnCO3/Mn3O4/RGO ternary composite with cycling. Furthermore, a systematic study of the potential difference of the redox reaction provides a good explanation for the observed electrochemical performance of the ternary composites.

Hydrazine-reduced graphite oxide and graphene oxide were synthesized to compare their performances as anode materials in lithium-ion batteries and sodium-ion batteries. Reduced graphite oxide inherits the layer structure of graphite, with an average spacing between neighboring layers (d-spacing) of 0.374 nm; this exceeds the d-spacing of graphite (0.335 nm). The larger d-spacing provides wider channels for transporting lithium ions and sodium ions in the material. We showed that reduced graphite oxide as an anode in lithium-ion batteries can reach a specific capacity of 917 mA h g−1, which is about three times of 372 mA h g−1, the value expected for the LiC6 structures on the electrode. This increase is consistent with the wider d-spacing, which enhances lithium intercalation and de-intercalation on the electrodes. The electrochemical performance of the lithium-ion batteries and sodium-ion batteries with reduced graphite oxide anodes show a noticeable improvement compared to those with reduced graphene oxide anodes. This improvement indicates that reduced graphite oxide, with larger interlayer spacing, has fewer defects and is thus more stable. In summary, we found that reduced graphite oxide may be a more favorable form of graphene for the fabrication of electrodes for lithium-ion and sodium-ion batteries and other energy storage devices.

We have designed and synthesized a unique structured graphene/SnO2 composite, where SnO2 nanoparticles are inserted in between interconnected graphene sheets which form hollow spherical multilayers. The hollow spherical multilayered structure provides much flexibility to accommodate the configuration and volume changes of SnO2 in the material. When it is used as an anode material for lithium-ion batteries, such a novel nanostructure can not only provide a stable conductive matrix and suppress the mechanical stress, but also eliminate the need of any binders for constructing electrodes. Electrochemical tests show that the unique graphene/SnO2 composite electrode as designed could exhibit a large reversible capacity over 1000 mA h g−1 and long cycling life with 88% retention after 100 cycles. These results indicate the great potential of the composite for being used as a high performance anode material for lithium-ion batteries.

We describe the structural parameters and atomic positions of a single-walled WS2 nanotube. The structure factor is calculated in detail using analytic expressions for both single-walled and multi-walled WS2 nanotubes. A zoning scheme has been developed to obtain the ratio m/n from the electron diffraction patterns. The procedure for determination of the chiral indices of both single-walled and multi-walled WS2 nanotubes and the tilt angle is illustrated in detail for either normal incidence or inclined incidence. As an example of application, the determination of the chiral indices of a five-shell WS2 nanotube was carried out and the tilt angle was obtained as 17.7°. The method developed here is useful and valid to determine the atomic structure of WS2 nanotubes.

The dramatically increased demand for electric devices such as electric vehicles and consumer electronics prompted us to explore new ideas in fabricating novel energy storage devices. In this work, we designed, constructed, and studied an asymmetric hybrid lithium-ion capacitor (LIC) by combining an electric double-layer capacitor cathode and a lithium-ion battery anode. Both electrodes were made of a single-wall carbon nanotube and graphene (SG) composite to reduce restacking of the graphene nanosheets, to improve the energy storage capacity, and to improve the electrical conductivity of the electrodes. One of the electrodes was pre-lithiated electrochemically. After pre-lithiation, the lithiated-SG (Li-SG) electrode showed excellent capacity in lithium intercalation and de-intercalation and was used as the anode of the LIC device. The advantage of the hybrid LIC with asymmetric graphene electrodes is that it maximizes the operable voltage between the two electrodes, thus increasing the energy density of the device. The hybrid LIC fabricated in this work exhibited an energy density of 222 W h kg−1 at a power density of 410 W kg−1.

Correction for ‘Roles of water in the formation and preparation of graphene oxide’ by Qiang Zhang et al., RSC Adv., 2021, 11, 15808–15816, DOI: 10.1039/D0RA10026A.

Graphene has been widely used as an electrode material for supercapacitors. However, parallelly-stacked graphene layers often result in inefficient ion diffusion and electron transfers that usually reduce the rate capability of a supercapacitor. In this study, reduced graphene oxide (rGO) and poly (3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) composite films were prepared by a solvent evaporation method using PEDOT:PSS as the binder to fix aligned graphene for its good conductivity and strong π-π stacking interactions with the graphene sheets. Analyses using scanning electron microscopy (SEM), nitrogen adsorption-desorption, and small-angle X-ray scattering show that the graphene sheets were well aligned when a magnetic field was applied, though they were oriented randomly without the magnetic field. As a capacitor electrode material, the aligned rGO shows a specific capacitance of 169 F g−1 with a capacitance retention of about 70% at a current density of 50 A g−1 and its cyclic voltammetry (CV) loops maintained a rectangular shape at a voltage scan rate of 2 V s−1. The aligned rGO electrode can help break through the limitations of traditional supercapacitors and increase significantly their charge/discharge rate and power density.

The graphene material prepared by the chemical reduction method usually has oxygenic functional groups in it and such functional groups often result in interactions between the graphene electrode and the electrolyte in supercapacitors. We have examined the existential form of interactions between graphene as the electrode and three kinds of ionic liquid, 1-ethyl-3-methylimidazolium bis (trifluoromethylsulfonyl) imide (EMI-TFSI), 1-ethyl-3-methylimidazolium tetrafluoroborate (EMI-BF 4 ), and 1-methyl-1-propylpiperidinium bis (trifluoromethyl sulfonyl) imide (MPPp-TFSI), as the electrolyte of a supercapacitor. Mass spectroscopy (MS) and Fourier transform infrared spectroscopy (FT-IR) analyses confirmed that the residual hydroxyl groups in graphene were transferred to EMI + and TFSI − lost oxygen atoms to graphene, while little reaction took place in BF 4 − or MPPp + , during the process of charging. The chemical reactions are suggested to contribute to the device capacitance while it is also one of the reasons for the decreased electrochemical stability window. In this study the highest energy density achieved using the graphene electrode is 169 Wh kg −1 in MPPp-TFSI electrolyte charged to 4.4 V.

〈100〉 Oriented zirconium carbide (ZrC) nanowires have been synthesized by chemical vapor deposition (CVD). A single ZrC nanowire emitter has been prepared for investigations of its field emission properties. A high field enhancement factor of 8.23 × 106 m−1 was obtained, attributed to the unique structure of the ZrC nanowire. Furthermore, the emitter exhibited a high emission current density of 6.92 × 1010 A/m2 at a low extraction voltage of 555 V, which is much lower than the voltage required for traditional cone shaped ZrC emitters. The results demonstrated that ZrC nanowires are of great advantages for field emission applications.

Silicon-based materials are showing appealing potentials for electrical energy storage because of their unparalleled theoretical energy density. In this work, a rapid and efficient surface-polymerization processing has been developed to obtain a sandwich-like silicon-carbon composite structure for fast lithium storage. The anchored silicon particles are connected with a low diffusion tortuosity in the designed structure that facilitates the electron transport throughout the electrode and enhances the response rate under high current density. Electrochemical measurements demonstrate that the silicon-carbon composite electrode exhibits a high capacity for lithium storage. It shows a reversible capacity of 1990 mA h g−1 at 0.5 C after 100 cycles and also has an excellent capacity retention property (only −0.062% capacity reduction per cycle) in long-term cycling at 1 C. Furthermore, it can deliver a high reversible specific capacity of 1170 mA h g−1 even at 4 C.

Silicon-based materials with high specific capacities have attracted great attentions as an alternative to graphite anode in lithium-ion batteries. However, the low electrical conductivity and inefficient suppression of volume expansion make it somewhat unsuitable for practical applications. Thence, a rapid self-encapsulating approach was first adopted to construct a conductive and effective carbon protective shell on the surface of layered SiOx-based nanosheets by compositing polyelectrolyte (polyethyleneimine, PEI) with graphene oxide (GO). This designed composite electrode has a compact and robust interfacial structure attributed to chemical integration and electrostatic interactions, which also greatly increased the tap density of the electrode. As an anode material, it delivered a high reversible capacity of 867 mAh g−1 and excellent rate capability. The cycling stability is also retained even after rate performance test, which resulted a −0.033% capacity decay rate for each cycle in 500 cycles.

To improve the lithium storage properties of anode in lithium ion capacitors (LICs), reduced graphene oxide (rGO) decorated with crystallized cobalt borate nanoparticles (Co-B/rGO) was prepared by an in-situ growth method. Microstructural characterizations demonstrate that crystallized Co-B nanoparticles not only act as an effective electron transfer bridge between rGO nanosheets but also provide more active sites for lithium storage. As a result, LIC based on Co-B/rGO anode exhibited stable cycling performance with a capacitance retention of 75% after 2000 cycles at 2000 mA g−1, and high energy and power density. Thus, Co-B/rGO can be a promising anode material for LICs.

The field-emission characteristics of zirconium carbide (ZrC) nanowire with an oxidized surface are studied. When the ZrC nanowire is processed to introduce an oxidized surface, its field-emission performance is improved significantly, exhibiting a high field-emission current and enhanced emission current stability with a fluctuation of 1.7% in a vacuum of 6 × 10−8 Pa. Furthermore, a reduced turn-on voltage of the ZrC nanowire after oxidation was observed in the field-emission measurement, which is attributed to a reduction of the work function of the ZrC nanowire after oxidation treatment. Density functional theory calculations have also been performed to validate the mechanisms responsible for the improvement of field-emission stability and reduction in the work function of the ZrC nanowire.

Silicon (Si) has been broadly investigated as a promising anode in lithium-ion batteries (LIBs). However, there is still a problem that the alloying reactions of Si and Li often cause structural failures and rapid degradation in capacity of the electrode. Herein, an in-situ encapsulation of Si nanoparticles forming metal-organic-framework (MOF) derived carbon shells has been developed to improve the performance and retain the structural integrity of the electrode. Using this strategy, a compact and robust interface was ensured between the Si nanoparticles and carbon shell while also reducing the unnecessary exposing areas simultaneously. Moreover, the pores in the MOF-derived carbon shells offered good channels for Li-ion penetration and diffusion. The resulted composite electrode exhibited excellent electrochemical performance and delivered a capacity of 3714 mAh g−1 at 200 mA g−1, and an outstanding reversible capacity of 820 mAh g−1 at 5000 mA g−1 even after 1000 cycles, Direct comparison between the encapsulated Si and naked Si revealed the significance of the MOF-derived carbon shells and its great potential for the next-generation high capacity LIBs.

Electron sources in the form of one-dimensional nanotubes and nanowires are an essential tool for investigations in a variety of fields, such as X-ray computed tomography, flexible displays, chemical sensors and electron optics applications. However, field emission instability and the need to work under high-vacuum or high-temperature conditions have imposed stringent requirements that are currently limiting the range of application of electron sources. Here we report the fabrication of a LaB6 nanowire with only a few La atoms bonded on the tip that emits collimated electrons from a single point with high monochromaticity. The nanostructured tip has a low work function of 2.07 eV (lower than that of Cs) while remaining chemically inert, two properties usually regarded as mutually exclusive. Installed in a scanning electron microscope (SEM) field emission gun, our tip shows a current density gain that is about 1,000 times greater than that achievable with W(310) tips, and no emission decay for tens of hours of operation. Using this new SEM, we acquired very low-noise, high-resolution images together with rapid chemical compositional mapping using a tip operated at room temperature and at 10-times higher residual gas pressure than that required for W tips.

Ionic liquids (ILs) with large electrochemical windows up to 4 V have been employed as the electrolyte to boost the energy density of graphene-based supercapacitors. However, due to the larger molecular size, lower conductivity, and higher viscosity of the IL electrolyte, graphene-based supercapacitors in IL electrolyte usually exhibit low rate capability. To make graphene-based electrodes more compatible with the IL electrolyte, we functionalized chemically reduced graphene oxide with the same IL which is also used as the electrolyte. Electrochemical test results show that the relaxation time and charge transfer resistance at electrode-electrolyte interface for IL modified electrode is one third and one fourth of that for the pristine graphene electrode, respectively, indicating the improved compatibility between the IL modified electrode and the electrolyte. Furthermore, the capacitance retention of the IL modified electrode from current density of 0.5 to 20 A g−1 is 85%, which is much higher than that of the pristine electrode (53%).

Carbon nanotube spaced graphene aerogels have been prepared by a hydrothermal method and used for supercapacitor applications. The specific surface area and specific capacitance can be controlled by tuning the amount of added carbon nanotubes. The as-prepared composite aerogels retain the advantage of aerogel structure in providing macropores to ensure electrodes fast wetted by the electrolyte ions and also possess additional mesopores created by the carbon nanotube spacers for more ion adsorption. Benefited from that, the composite aerogels exhibit significantly enhanced supercapacitor properties in both aqueous and ionic liquid electrolyte. Compared with graphene aerogels, the composite aerogels show a 37% larger specific capacitance of 245.5 F g � 1 at a current density of 2.5 A g � 1 and high rate capability of 197.0 F g � 1 at a high current density of 80 A g � 1 in aqueous electrolyte. Moreover, the composite aerogels deliver a 33% larger specific capacitance of 183.3 F g � 1 at 0.5 A g � 1 and a high energy density of 80 Wh kg � 1 when using an ionic liquid (EMIMBF4) as the electrolyte.

We describe the structural parameters and atomic positions of a single-walled WS

We have designed and synthesized a unique structured graphene/SnO

Single- and double-walled WS2 nanotubes of small diameter (

We describe preparation and characterization of nanostructured electrodes using Co(OH)2 nano-flakes and carbon fiber cloth for supercapacitors. Nanostructured Co(OH)2 flakes are produced by electrodeposition and they are coated onto the electro-etched carbon fiber cloth. A highest specific capacitance of 3404.8 F g−1 and an area-normalized specific capacitance of 3.3 F cm−2 have been obtained from such electrodes. Morphology and structure of the nanostructured electrodes have been characterized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The electrochemical properties have been studied by cyclic voltammetry (CV), constant-current charge and discharge, electrochemical impedance spectroscopy (EIS), and long-time cycling.

We have synthesized graphene by reducing carbon dioxide in magnesium and calcium metal flames. The as-prepared graphene has been used as conductive additive to improve the electrical conduction of activated carbon-based supercapacitor electrodes. The graphene/activated carbon composite electrode showed an outstanding specific capacitance of 220 and 180 F g (1) at a current density of 0. 1 A g (1) in 6 M KOH electrolyte when using graphene obtained in magnesium and calcium flames, respectively. (C) 2013 Elsevier B.V. All rights reserved.

Graphene and single-walled carbon nanotube (SWNT) composite aerogel has been prepared by hydrothermal synthesis. The restacking of graphene is effectively reduced by SWNTs inserted in between graphene layers in order to make available more active sites and reactive surface area. Electrochemical experiments show that the graphene–SWNT composite electrode has superior catalytic performance in selective detection of uric acid (UA).

Graphene and single-walled carbon nanotube (CNT) composites are explored as the electrodes for supercapacitors by coating polyaniline (PANI) nano-cones onto the graphene/CNT composite to obtain graphene/CNT–PANI composite electrode. The graphene/CNT–PANI electrode is assembled with a graphene/CNT electrode into an asymmetric pseudocapacitor and a highest energy density of 188 Wh kg−1 and maximum power density of 200 kW kg−1 are achieved. The structure and morphology of the graphene/CNT composite and the PANI nano-cone coatings are characterized by both scanning electron microscopy and transmission electron microscopy. The excellent performance of the assembled supercapacitors is also discussed and it is attributed to (i) effective utilization of the large surface area of the three-dimensional network structure of graphene-based composite, (ii) the presence of CNT in the composite preventing graphene from re-stacking, and (ii) uniform and vertically aligned PANI coating on graphene offering increased electrical conductivity.

We describe a process of co-reduction to reduce dispersed graphene oxide (GO) and single-walled carbon nanotubes (SWNTs) simultaneously for preparation of hybrid electrodes for graphene supercapacitors. The SWNTs are in between the inter-layer space of graphene sheets as a spacer to prevent effectively restacking of graphene that often limits seriously the electrochemical performance of graphene supercapacitors. The SWNTs also act as conductive binders to improve the electrical conduction of the electrode. A high specific capacitance of 261 F g−1 for a single electrode and specific energy density of 123 W h kg−1 measured in the two-electrode configuration have been obtained in ionic liquid (EMI-TFSI).

Few-layer graphene has been prepared by electrochemical intercalation of graphite cathode using Na + / dimethyl sulfoxide complexes as intercalation agent. By adding thionin acetate salt into the electrolyte, the exfoliated graphite is stabilized and further exfoliated into few-layer graphene. Raman and X-ray photoelectron spectra indicate that the graphene material has lower content of defects and oxygen functional groups compared with that obtained by chemically reducing graphene oxide. The graphene paper produced by filtration shows an electrical conductivity of 380 S m 1 , which is forty times larger than that of the graphene material produced by chemical reduction of thionin-stabilized graphene oxide.

Electrical devices based on suspended multi-wall carbon nanotubes were constructed and studied. The chiral structure of each shell in a particular nanotube was determined using nanobeam electron diffraction in a transmission electron microscope. The transport properties of the carbon nanotube were also measured. The nanotube device length was short enough that the transport was nearly ballistic, and multiple subbands contributed to the conductance. Thermal excitation of carriers significantly affected nanotube resistance at room temperature.