The optimization of the electrodes structure is crucial for supercapacitors. Herein, we report a novel three-dimensional (3D) hierarchical multihole architecture of ternary reduced graphene oxide (rGO)/MnO2/carbon foam (CF) nanocomposites. Thereinto, CF not only firstly serves as conductive skeleton but also offers primary pore structure with nickel foam and supporter for electrochemical deposition (ECD) of MnO2. Furthermore, rGO covered on electrodes surface both prevents the exfoliation of MnO2 and integrates with it to construct secondary pore structure. The configuration with three components synergistic effects leads to a high specific capacitance of 356.5 F g−1 at a scan rate of 10 mV s−1 and a long cycle life along with 93.6% specific capacitance retained after 2000 cycles. Also, it even remained 30.6 Wh kg−1 at a large power density of 13.5 kW kg−1.

•Mullite whisker networks were facilely prepared by direct sintering of coal fly ash.•Morphology evolution process and growth characteristics of mullite whisker networks were significantly affected by additive.•High strength low density ceramic proppants with mullite whisker network structure were sintered at1350 °C.•This mullite-based proppant has great potential for wide use in oil and gas production.This work presents a simple approach to produce controlled mullite whisker network structure. Mullite whisker networks were facilely prepared by direct sintering of coal fly ash, bauxite and kaolin in BaCO3-potash feldspar-pyrolusite-talcum catalytic system at 1350 °C. Controlled mullite whiskers were obtained with about 200 nm in diameter and 3 μm in length by controlling the rate of Al2O3 diffusion through feldspar addition in catalytic system. Morphology evolution process and growth characteristics of mullite whisker networks were further investigated using scanning electronic microscope (SEM) and their possible fabrication mechanism were also investigated. The optimum mullite whisker network structural material exhibits some attractive properties such as high strength (199.89 MPa), low density (1.51 g cm−3) and low acid solubility (2.63 wt%). These results demonstrate an effective method to prepare large-scale mullite whisker network with potential applications in producing ceramic proppants.Download high-res image (266KB)Download full-size image

•High strength lightweight mullite whiseker network reinforced ceramic materials was successfully prepared from coal fly ash.•The shape and size of mullite crystals was controllable by adjusting the firing temperature and additive.•High strength lightweight mullite-based ceramic were sintered at1390 °C.•This mullite ceramic has great potential for wide use in proppant production.High strength lightweight mullite whisker network reinforced ceramic materials was successfully prepared by firing a bauxite - kaolin - coal fly ash mixture with additions of varying mixtures of feldspar - talcum - BaCO3 - pyrolusite. The mullite whisker network exhibits a unique architecture in which thin mullite crystals layers with anisotropic properties and well controlled crystal size were interweaved with one another. The effects of pyrolusite content on morphologies and properties of resultant ceramic materials were investigated. The phase compositions and microstructures of several samples were investigated by X-ray powder diffraction (XRD) and scanning electron microscopy (SEM). The flexural strength and acid solubility of ceramic materials as functions of sintering temperature were systematically investigated by measuring the flexural strength and acid solubility at different sintering temperature, respectively. The resulting mullite whisker network structure ceramic materials showed optimum performance at sintering temperature around 1390 °C when the content of pyrolusite equals to 6 wt%, such as high strength (190.10 MPa), low density (1.48 g cm−3) and low acid solubility (2.55 wt%). The approach opens new opportunities for the sintered ceramic as a proppant material since the ceramic system displays low acid solubility and good flexural strength.

•Two-step approach of fabrication of 3D MnO2-graphene-carbon nanotubes.•MnO2-graphene oxide is served as a substrate to immobilize CNT.•The 3D MnO2-graphene-carbon nanotubes as supercapacitor electrode with binder-free.•The 3D MnO2-graphene-carbon nanotubes shows high energy density.This paper describes the fabrication and characterization of a three-dimensional (3D) MnO2-graphene (GR)-CNT hybrid obtained by combining electrochemical deposition (ELD)-electrophoretic deposition (EPD) and chemical vapor deposition (CVD). Firstly, 3D MnO2-graphene oxide (GO) is fabricated via ELD-EPD. Secondly, the catalyst and xylene are mixed with solution of certain concentration. Thirdly, catalyst is loaded on the surface of MnO2-GO when the solution is sprayed into the furnace. Forth, MnO2-GO is restored to MnO2-GR at high temperature, meanwhile, MnO2-GR is served as a substrate to grow CNT, which is beneficial to provide high speed channel for carrier and obtain pseudocapacitance of MnO2. The as-prepared hybrid is characterized by scanning electron microscope (SEM), transmission electron microscope (TEM), X-ray Diffraction (XRD) and Raman spectroscopy (Raman), and their supercapacitor properties are also investigated. The results show that a high specific capacitance of 330.75 F g−1 and high energy density of 36.68 Wh kg−1 while maintaining high power density of 8000 W kg−1 at a scan rate of 200 mV s−1. Furthermore, the hybrid displays a high specific capacitance of 187.53 F g−1 at ultrahigh scan rate of 400 mV s−1. These attractive results demonstrate that the hybrid is a promising electrode material for high performance supercapacitors.

•3D rGO-CNTs-NF electrode is fabricated by combination of EPD and FCCVD.•EPD with excellent uniformity is an economical processing technique.•FCCVD is beneficial to obtain more compact and uniform VACNTs.•The hybrid shows a high specific capacitance of 236.18 F g−1 and a high energy density of 19.24 Wh kg−1.•This work provides various assumptions for designing hierarchical rGO-based architecture.A facile method is designed to prepare 3D reduced graphene oxide (rGO) - carbon nanotubes (CNTs) - nickel foams (NF). In this research, the 3D rGO-CNTs-NF electrode is fabricated by combination of electrophoretic deposition and floating catalyst chemical vapor deposition. The vertically-aligned CNTs forests not only effectively prevent stacking of rGO sheets but also facilitate the electron transfer during the charge/discharge process and contribute to the whole capacitance. Moreover, the 3D rGO-CNTs-NF hybrid can be used directly as electrodes of supercapacitor without binder. Additionally, the hybrid shows a specific capacitance of 236.18 F g−1 which is much higher than that of the rGO - NF electrode (100.23 F g−1). Importantly, the energy density and power density of 3D rGO-CNTs-NF are respectively as high as 19.24 Wh kg−1 and 5398 W kg−1, indicating that our work provides a way to design hierarchical rGO-based architecture composed of rGO, CNTs and various electroactive materials for high-performance energy storage devices.

The composite of carbon foam with Ni-Zn ferrite as additive has been developed via foaming and carbonization process for electromagnetic interference shielding, using coal tar pitch as precursor and Ni-Zn ferrite as an additive. It was observed that the shielding effectiveness (SE) over the X-band frequency is enhanced along with the increase of Ni-Zn ferrite additive amount. The carbon foam with 15 wt% Ni-Zn ferrite shows a SE of 42 dB, which has a promising application prospect. The electromagnetic interference shielding mechanism of carbon foam with different amount of Ni-Zn ferrite additive is discussed in the work. An absorption-dominant mechanism, which is mainly associated with the magnetic property determined by the amount of Ni-Zn ferrite additive, has been revealed. It is also found that the mechanical strength of resultant carbon foams increases firstly and then decreases with the continuously increased amount of Ni-Zn ferrite additive.

Polymer matrices with excellent mechanical properties, thermal stability and other features are highly demanded for the effective utilization within nanocomposites. Here, we fabricate free-standing aramid nanofiber films via spin coating of an aramid nanofiber/dimethyl sulfoxide solution. Compared with traditional film fabrication methods, this process is time-saving and also able to easily tune the thickness of the films. The resultant films show greatly improved stretchability than that of Kevlar threads and relatively high mechanical strength. Typically, these films with a thickness of 5.5 µm show an ultimate strength of 182 MPa with an ultimate tensile strain of 10.5%. We also apply a finite element modeling to simulate the strain and strength distributions of the films under uniaxial tension, and the results of the simulation are in accordance with the experimental data. Furthermore, the aramid nanofiber films exhibit outstanding thermostability (decomposition at ~ 550 °C under N2 atmosphere and ~ 500 °C in air) and chemical inertness, which would endure acid and alkali. The simple method demonstrated here provides an important way to prepare high-performance aramid nanofiber films for designing new composite systems.

The reduction of graphene oxide was promoted remarkably under pressure via low temperature thermal treatment. Traditionally, graphene oxide is usually reduced in a preheated high temperature environment as a precondition of the thermal reduction. We report a pressure promoted method for low temperature thermal reduction and exfoliation of graphene oxide in large quantity at 260 °C. The physicochemical properties of parent graphite, as well as the microstructure and physicochemical properties of graphene oxide and resultant graphene were investigated by Raman spectrometer, thermograviment analyzer (TGA), transmission electron microscope (TEM), X-ray diffractometer (XRD) and Fourier transform infrared spectroscopy (FT-IR). Results show that graphene oxide was reduced to graphene with less stack via low-temperature pressure promoted thermal treatment, meanwhile, the degree of disorder reduced: the ratio of ID/IG in Raman spectrum decreases from 0.64 to 0.56. Moreover, graphene derived from low-temperature pressure promoted treatment exhibit better thermal stability than graphene oxide, and oxygen functional groups were removed with a high level. All of results exhibit improved comprehensive properties than graphene synthesized via traditional thermal reduction at 1000 °C.

•The variation tendency of secondary QI content is researched.•The relation between secondary QI content and the cellular structure is disclosed.•It is expected to optimizing the secondary QI content to form appropriate size pores so that to obtain carbon foams with high performance.Carbon foam was produced using mesophase pitches obtained under different temperatures as precursors, via foaming and carbonization process. The physicochemical properties of mesophase pitch, as well as the microstructure and physical properties of carbon foam were investigated by optical microscope, infrared spectrometer, thermograviment analyzer (TGA), X-ray diffractometer (XRD), scanning electron microscope (SEM) and universal testing machine, respectively. The results show that the amount of secondary quinoline insoluble in mesophase pitches increase with heat-treatment temperature increase, meanwhile, the cell size of carbon foams increased firstly and then reduced. Moreover, the compressive strength of carbon foams also exhibited the same variation trend. The cellular structure of carbon foam can be severely affected by the secondary quinoline insoluble content of mesophase pitch; thus it is critical to tailor the secondary quinoline insoluble content of mesophase pitch for obtaining carbon foam with high performance.

Parent coal tar pitch (CTP) was modified with boric acid (BA), cinnamaldehyde (CMA) and the mixture of BA and CMA, respectively. The parent CTP and three modified CTPs were characterized by elemental analysis, thermogravimetric analysis, Fourier transform infrared (FT-IR) spectroscopy and scanning electron microscopy. The four samples were carbonized at different temperatures and resultant carbonized products were characterized by FT-IR spectroscopy, X-ray diffraction and polarized-light microscopy. The results show that the morphologies and carbonization behaviors of the parent CTP and modified CTPs are quite different. The carbonization yield of the CTP modified with the mixture of BA and CMA is higher than that of CTP modified with BA or CMA only. In addition, the modification of CTP with 7 g of BA and 10 ml of CMA results in an increase in carbonization yield by 5.64%. During the pyrolysis of modified CTPs, the dehydration of BA or the distillation of CMA occurs at the temperature lower than 300 °C, and methyl and methylene groups of the modified CTPs disappear gradually as temperature rises. Furthermore, the modification of CTP by the mixture of BA and CMA results in more intensive mesophase spheres than other modified CTPs, and the modified CTP is easier to be carbonized to form graphitic carbon.

•The flexible 3D RGO-CNT-CF hybrid is fabricated by a combination of EPD and FCCVD.•The flexible hybrid displays a better electrochemical stability under different bending angles.•The flexible hybrid as supercapacitor electrode with binder-free.•This work paves a new road for us to fabricate new nanocomposites with hierarchical structures.In this work, reduced graphene oxide (RGO) - carbon nanotubes (CNT) grown on carbon fiber (CF) is fabricated by a combination of electrophoretic deposition (EPD) and chemical vapor deposition (CVD). Firstly, CF-GO composite is prepared via EPD. Secondly, the CF-RGO-CNT hybrid is obtained by floating catalyst chemical vapor deposition method for synthesizing CNT on the CF-RGO substrate. The as-prepared three-dimensional (3D) hierarchical hybrid shows strong mechanical stability and high flexibility at various bending angles. Furthermore, the hybrid is characterized by scanning electron microscope, X-ray Diffraction and Raman spectroscopy, and its supercapacitor properties are also tested. The electrochemical measurements display a higher specific capacitance of 203 F g−1, 4 times higher than that of pure CF. Importantly, the hybrid shows high electrochemical stability at various bending angles, and can be directly served as flexible electrode with binder-free for high-performance supercapacitors. All these attractive results indicate that the as-prepared 3D hybrid is a promising candidate for flexible supercapacitor applications.