Peiwei Gong

Design and synthesis of Ni-MOF/CNT composites and rGO/carbon nitride composites for an asymmetric supercapacitor with high energy and power density

Currently, metal–organic frameworks (MOFs) have been attracting great interest as a new kind of electrode material for energy storage devices, because their porous skeleton would benefit the access and transport of electrolytes, and the exposure of metal ions can offer more active sites to electrolytes. In this study, we have successfully fabricated nickel metal–organic framework/carbon nanotube (Ni-MOF/CNT) composites, which show excellent electrochemical performance due to the synergistic effects of the Ni-MOF specific structure and CNTs with high conductivity, achieving a high specific capacitance of 1765 F g−1 at a current density of 0.5 A g−1. To further explore the capacitive performance of the composite electrode, an asymmetric supercapacitor device using Ni-MOF/CNTs as the positive electrode and reduced graphene oxide/graphitic carbon nitride (rGO/g-C3N4) as the negative electrode was fabricated, and this device could be operated in a working voltage range of 0–1.6 V based on a complementary potential window in 6 M KOH aqueous electrolyte, delivering a high energy density of 36.6 W h kg−1 at a power density of 480 W kg−1. Moreover, this asymmetric supercapacitor revealed an excellent cycle life along with 95% specific capacitance retention after 5000 consecutive charge–discharge tests. These outstanding performances would make MOFs become one of the most promising candidates for the future high energy storage systems.

One-pot sonochemical preparation of fluorographene and selective tuning of its fluorine coverage

Fluorographene (FG), which inherits the properties of graphene and fluorographite (FGi), holds great promise for applications in high-performance materials and devices, including lubricants, nanocomposites, batteries, and nanoelectronics. However, challenges for realizing large-scale preparation and little knowledge concerning FGs physicochemical properties hinder its practical applications. Here, a novel and feasible method is developed to prepare FG through a simple sonochemical exfoliation process in N-methyl-2-pyrrolidone (NMP). Interestingly, FG at a high concentration in NMP displays dramatic stability without any additional stabilizer or modifier, and the C/F ratio of FG can be facilely tuned just by adjusting the sonochemical time. Furthermore, the electrochemical and thermal properties of the prepared FG have been systematically investigated and exhibited regularity with variation of fluorine coverage. On the other hand, based on the solubility of FG in various solvents, a possible dispersion mechanism is proposed to guide FGs further applications in films or polymer-based composites as a mechanical reinforcement.

Cooperatively exfoliated fluorinated graphene with full-color emission

We report a novel and effective method to prepare fluorinated graphene sheets (FGS) by the cooperative exfoliation of graphite fluoride using cetyl-trimethyl-ammonium bromide and dopamine. This facile, scalable preparation route results in wide (about 2 μm in width), long (at least 3 μm in length) and ultrathin (1–2 layers) FGS with uniform morphology. The chemical composition of FGS was characterized by X-ray photoelectron spectroscopy and energy dispersive X-ray spectroscopy. The obtained FGS exhibits full-color emission when excited by near ultraviolet (NUV) rays, suggesting its potential applications in luminescence devices, such as NUV-pumped FGS-based flexible light-emitting diodes.

Photochemical synthesis of fluorinated graphene via a simultaneous fluorination and reduction route

We have explored a novel photochemical route to synthesize fluorinated graphene via simultaneously fluorinating and reducing graphene oxide (GO) in HF solution at room temperature. This method avoids special equipment, employs simple UV irradiation and utilizes readily available GO as the carbon source.

Structural and tribological characterization of fluorinated graphene with various fluorine contents prepared by liquid-phase exfoliation

The high strength and noble inertness of fluorinated graphene (FG) indicate very promising properties for its application in tribological applications to reduce friction and save energy, yet few works refer to its tribological performance, mostly due to the lack of an effective synthesis method and limited knowledge of FG. In this work, fluorinated graphene (FG) sheets with various fluorine contents are prepared from fluorinated graphite (FGi) by means of controllable chemical reaction with ethylenediamine (EDA) and liquid-phase exfoliation with N-methyl-2-pyrrolidone (NMP) in a one-pot synthesis. Transmission electron microscopy and atomic force microscopy analyses show that the obtained FG sheets possess large lateral size and ultrathin thickness (1.8–4.0 nm). Chemical characterizations indicate the C/F ratio can be readily tuned by adjusting the reaction temperature with EDA, which leads to defluorination and also substitution of a small amount of fluorine atoms by alkylidene amino groups. The tribological performance of FG samples as novel lubricant additives in base oil of polyalphaolefin-40 with different concentrations (0.1–0.4 mg mL−1) is investigated. The tribological tests suggest that the addition of FG at optimum concentration can greatly improve the anti-wear property of the base oil and there exists a strong proportional relationship between anti-wear ability and fluorine content.

Scalable fabrication of high quality graphene by exfoliation of edge sulfonated graphite for supercapacitor application

Graphene sheets with high quality and dispersibility were prepared by exfoliation of edge sulfonated graphite. Tosyl-graphene (TsG) dispersion in N-methyl-pyrrolidone (NMP) readily reached up to 16 mg mL−1 without any surfactants. TsG enjoys intact crystal planes and flexible framework. When employed as electrode material for supercapacitor, TsG shows outstanding specific capacitance of 180 F g−1 at a current density of 0.5 A g−1, and excellent cycling stability (only 2% loss after 10 000 cycles), which can offer enormously potential for super-capacitors and other highly desired energy storage devices.

High efficiency shear exfoliation for producing high-quality, few-layered MoS2 nanosheets in a green ethanol/water system

This work presented a feasible strategy to generate molybdenum disulfide (MoS2) nanosheets by a direct liquid shear exfoliation technique in a green mixed solvent system of ethanol/water. The volume ratio of ethanol/water and the initial concentration of the bulk MoS2 powders were found to have significant impacts on the final exfoliation yield. The best ratio and initial concentration for optimal shear exfoliation were finally selected as 45 vol% and 10 mg mL−1, respectively. According to the proper shear strength and matching viscosity, systematic analysis on the exfoliation mechanism indicated that shear and collision effects would play the major role when the shearing occurred at a high speed of 10 000 rpm. The higher cumulative yield and better quality (up to 30% after 10 times of shear cycling, comparatively large sizes d ∼ 4 μm) were confirmed by detailed experimental characterizations. Moreover, the photothermal performance was also investigated and the prepared MoS2 nanosheets exhibited great efficiency in transforming near-infrared light into heat. It is expected to be a promising strategy for large-scale production of MoS2 nanosheets with excellent properties in a low-cost and green solvent system.

Photoluminescent carbon quantum dot grafted silica nanoparticles directly synthesized from rice husk biomass

In this work, carbon quantum dot grafted silica nanoparticles (silica-C NPs) are directly synthesized from rice husk biomass with high yield. The rice husk derived silica-C NPs exhibit outstanding features, including ease of surface modification, high water dispersibility, and biocompatibility. Due to the covalent decoration of the carbon framework, the wide band gap amorphous silica is endowed intense and unique photoluminescence, which can be well controlled by further adjustments. Detailed investigations suggest that the silica-C NPs have the inherent advantages of both silica and carbon quantum dots, which ideally addresses the widely recognized issues of conventional silica-based photoluminescent nanomaterials for biomedical applications. In addition to creating a novel silica-based nanostructure with prominent performances, this work achieves the comprehensive utilization of rice husk biomass, which shows significant economic and environmental benefits.

Design and fabrication of carbonized rGO/CMOF-5 hybrids for supercapacitor applications

A reduced graphene oxide/carbonized metal–organic framework (rGO/CMOF-5) hybrid with an rGO inner layer and an outer cover of CMOF-5 was successfully fabricated by combining a simple solvothermal reaction with an annealing treatment. The resulting rGO/CMOF-5 hybrid had a high specific surface area (2040 m2 g−1) and a reasonable porous structure and showed improved electrochemical performance when used as a novel supercapacitor electrode material. Electrochemical tests showed that the rGO/CMOF-5 hybrid achieved an impressive specific capacitance of 312 F g−1 at a current density of 0.5 A g−1 in an alkaline electrolyte and an outstanding cycle stability (retaining 89% capacitance after 5000 cycles) and favorable rate capability with 59% retention after a 40-fold increase. A symmetrical supercapacitor based on the rGO/CMOF-5 hybrid delivered a high energy density of 17.2 W h kg−1 at a power density of 250 W kg−1 and retained 81% of its initial capacitance at a current density of 2 A g−1 after 5000 charge–discharge cycles. These results indicate that this hybrid could be used in electrochemical energy storage and gave new insights into the design and utilization of aged carbon materials with remarkable performances.