Qing-Qiang Kong

Macroporous ‘bubble’ graphene film via template-directed ordered-assembly for high rate supercapacitors

A three-dimensional bubble graphene film, with controllable and uniform macropores and tailorable microstructure, was fabricated by a facile hard templating strategy and exhibit extraordinary electrochemical capacitance with high rate capability (1.0 V s(-1)).

Hierarchical porous carbon microtubes derived from willow catkins for supercapacitor applications

With willow catkins as highly accessible carbon sources, hierarchical porous carbon microtubes (denoted as HPNCTs) have been successfully prepared by a facile carbonization and subsequent KOH activation process. The resulting materials not only inherited the natural tubular morphology of willow catkins, but also developed a hierarchical porous structure by activation, with nitrogen from the biomass being self-doped in the resulting carbon. A maximum specific surface area of 1775.7 m2 g−1 with a pore volume of 0.8516 cm3 g−1 was achieved for HPNCT-800. When evaluated as an electrode by a three-electrode system in 6 M KOH aqueous solution, the material exhibited a high gravimetric capacitance of 292 F g−1 at a current density of 1 A g−1, with a good rate capability of 83.5% retention at 10 A g−1. HPNCT-800 was further employed in a coin-type symmetric device with 1 M LiPF6 electrolyte, and exhibited a high energy density of 37.9 W h kg−1 at a power density of 700 W kg−1, with excellent cycling stability with 90.6% retention after 4000 cycles. By taking advantage of the unique structure of abundant biomass from nature, this work sheds light on the creation of advanced porous carbon materials towards energy storage applications.

Thermally reduced graphene oxide films as flexible lateral heat spreaders

A thermally reduced graphene oxide film (r-GOF), with tailorable micro-structures and macro-properties, is fabricated by annealing a filtrated graphene oxide film (GOF) in a confined space. The structural evolution of the film at different annealing temperatures is systematically investigated, and further correlated to the thermal conductivity and mechanical performances. With the increase of temperature, more oxygen-containing functional groups are removed from the film by a simultaneous conversion from sp3 to sp2 carbon in the graphitic lattice. As the temperature reached 1200 °C, the r-GOF achieves an ultrahigh thermal conductivity of ca. 1043.5 W m−1 K−1, while 1000 °C is a critical temperature in enhancing the thermal conductivity. Moreover, G1200 exhibits excellent mechanical stiffness and flexibility with a high tensile strength (13.62 MPa) and Youngs modulus (2.31 GPa). The combined conductivity and mechanical performances render the r-GOFs promising materials as flexible lateral heat spreaders for electronics.

Self‐Assembled 3D Graphene‐Based Aerogel with Co3O4 Nanoparticles as High‐Performance Asymmetric Supercapacitor Electrode

Using graphene oxide and a cobalt salt as precursor, a three-dimensional graphene aerogel with embedded Co3 O4 nanoparticles (3D Co3 O4 -RGO aerogel) is prepared by means of a solvothermal approach and subsequent freeze-drying and thermal reduction. The obtained 3D Co3 O4 -RGO aerogel has a high specific capacitance of 660 F g(-1) at 0.5 A g(-1) and a high rate capability of 65.1 % retention at 50 A g(-1) in a three-electrode system. Furthermore, the material is used as cathode to fabricate an asymmetric supercapacitor utilizing a hierarchical porous carbon (HPC) as anode and 6 M KOH aqueous solution as electrolyte. In a voltage range of 0.0 to 1.5 V, the device exhibits a high energy density of 40.65 Wh kg(-1) and a power density of 340 W kg(-1) and shows a high cycling stability (92.92 % capacitance retention after 2000 cycles). After charging for only 30 s, three CR2032 coin-type asymmetric supercapacitors in series can drive a light-emitting-diode (LED) bulb brightly for 30 min, which remains effective even after 1 h.

Graphene Oxide Catalyzed Dehydration of Fructose into 5‐Hydroxymethylfurfural with Isopropanol as Cosolvent

The design of green heterogeneous catalysts for the efficient conversion of biomass into platform molecules is a key aim of sustainable chemistry. Graphene oxide prepared from Hummers oxidation of graphite was proven to be a green and efficient carbocatalyst for the dehydration of fructose into 5‐hydroxymethylfurfural (HMF) in some three‐carbon and four‐carbon alcohol mediated solvent systems. HMF was obtained in up to 87 % yield in 90 vol % isopropanol‐mediated DMSO solvent. Some control experiments and analytical data showed that a small number of sulfonic groups and abundance of oxygen‐containing groups (alcohols, epoxides, carboxylates) have an important synergic effect in maintaining the high performance of graphene oxide.

Crumpled reduced graphene oxide by flame-induced reduction of graphite oxide for supercapacitive energy storage

A novel flame-induced synthesis approach was developed to prepare crumpled reduced graphene oxide (rGO) from graphite oxide (GO) powder with the assist of flammable polar solvents such as methanol, ethanol and acetone under ordinary conditions. The as-prepared methanol–rGO, ethanol–rGO and acetone–rGO exhibit a high surface area of 421, 500 and 384 m2 g−1, respectively. The method is highly attractive for the mass production of graphene due to its simplicity, high efficiency, energy saving property and cost-effectiveness. The thermal exfoliation and reduction of GO powder, as well as the morphology and surface chemistry of resulting rGO, were related to the volatility, infiltration and combustion heat of the solvents. The electrochemical properties of the rGO samples were further evaluated in a 6 M KOH aqueous electrolyte. In a three-electrode setup, the corresponding specific capacitance of methanol–rGO, ethanol–rGO and acetone–rGO was calculated to be 260, 221 and 200 F g−1 at a current density of 0.1 A g−1, respectively. Moreover, the flame-reduced methanol–rGO exhibited a maximum energy density of 68.85 W h kg−1 as tested in a two-electrode system. The excellent supercapacitive performance of the methanol–rGO and ethanol–rGO materials is attributable to the combination of high surface area, residual oxygen containing groups and wrinkled morphologies.

Hollow carbon microtubes from kapok fiber: structural evolution and energy storage performance

Hollow carbon microtubes, with tunable porosity and surface chemistry, are highly desired for advanced energy conversion and storage applications. Although most natural fibers possess a hollow tubular structure, their original morphology is easily destroyed when they are carbonized directly due to the pyrolysis reactions. In this study, using kapok fiber as a precursor, hollow carbon microtubes were obtained by pre-stabilization and subsequent carbonization–activation in the presence of (NH4)2HPO4. During structural evolution from an organic biomass fiber to a hollow carbon fiber, (NH4)2HPO4 acts not only as a porogen and nitrogen/phosphorus source for in situ activation and doping but also as a crosslinking agent for chemical stabilization. The material exhibited good electrochemical performance in an organic electrolyte when evaluated as a supercapacitor electrode due to highly accessible surface area, convenient ion diffusion, and electron transfer. This study provides insights for the design of an anisotropic porous carbon structure towards next-generation high-power smart devices.

From two-dimensional to one-dimensional structures: SiC nano-whiskers derived from graphene via a catalyst-free carbothermal reaction

One-dimensional β-SiC nano-whiskers are synthesized from two-dimensional graphene by a facile catalyst-free carbothermal reaction. Comparing with closed or semi-closed carbon sources, the large exterior surface area and exposed rich edge render graphene an ideal carbon source for the scale-up production of carbide materials.

Graphene oxide aerogels constructed using large or small graphene oxide with different electrical, mechanical and adsorbent properties

The performances of graphene oxide aerogels (GOA) are studied by constructing them using different lateral sizes of graphene oxide (GO). Gelatinization of GO hydrosol is realized using a cross-linking agent, poly(vinyl alcohol) (PVA), and then solution-freeze-lyophilization is carried out to construct the cross-linking network of GOA. The contact points in GOA constructed using large sized GO (GOA325) were fewer than those in the GOA using small sized GO (GOA10000). It is the contact points that decide the micro-structure of GOA, and hence the performances. The size effect of the structural units is studied by investigating the electrical conductivity, mechanical strength, and adsorption capacity. The electrical conductivity of GOA325 can reach 0.78 S m−1 after carbonization at 800 °C, which was much higher than that of carbonized GOA10000 (0.53 S m−1). The compression modulus of GOA325 was 0.51 MPa, while the value for GOA10000 was 0.04 MPa. The adsorption capacity of GOA325 was also higher than that of GOA10000 for adsorbing both hydrophilic and oleophilic media.

Effect of annealing temperature on the mechanical properties of flexible graphene films

Abstract Free-standing graphene films (GFs) as functional materials require high mechanical performance for a convenient industrial processing. GFs were prepared from graphene oxide films by annealing temperatures from 1300 to 1700 °C, and were characterized by AFM, XRD, SEM, Raman spectroscopy and mechanical testing. Results indicate that the samples have a maximum tensile strength and fracture strain of 22.41 MPa and 2.44%, respectively and a minimum thermal conductivity of 744 W m−1 K−1 for an annealing temperature at 1500 °C. This is related to physical interlocking which results, from surface wrinkles of the graphene layers.