The Micron-Droplet-Confined Continuous-Flow Synthesis of Freestanding High-Entropy-Alloy Nanoparticles by Flame Spray Pyrolysis.

Alloying multiple immiscible elements into a nanoparticle with single-phase solid solution structure (high-entropy-alloy nanoparticles, HEA-NPs) merits great potential. To date, various kinds of synthesis techniques of HEA-NPs are developed; however, a continuous-flow synthesis of freestanding HEA-NPs remains a challenge. Here a micron-droplet-confined strategy by flame spray pyrolysis (FSP) to achieve the continuous-flow synthesis of freestanding HEA-NPs, is proposed. The continuous precursor solution undergoes gas shearing and micro-explosion to form nano droplets which act as the micron-droplet-confined reactors. The ultrafast evolution (<5 ms) from droplets to <10 nm nanoparticles of binary to septenary alloys is achieved through thermodynamic and kinetic control (high temperature and ultrafast colling). Among them, the AuPtPdRuIr HEA-NPs exhibit excellent electrocatalytic performance for alkaline hydrogen evolution reaction with 23 mV overpotential to achieve 10 mA cm-2, which is twofold better than that of the commercial Pt/C. It is anticipated that the continuous-flow synthesis by FSP can introduce a new way for the continuous synthesis of freestanding HEA-NP with a high productivity rate.

Methane hydrate efficient formation in a 3D-rGO/SDBS composite.

The optimization of storage space and material composition can significantly improve the generation rate and storage capacity of methane hydrate, which is important for the industrial application of solidified natural gas (SNG) technology. In our report, the effects of the presence of SDBS (sodium dodecylbenzene sulfonate), GO (graphene oxide), 3D-rGO (3D-reduced graphene oxide) and 3D-rGO/SDBS (3D-reduced graphene oxide/sodium dodecylbenzene sulfonate) on the methane hydrate generation process are investigated. The results show that the heterogeneous effect on the solid-phase surface of 3D-rGO/SDBS and its interconnected three-dimensional (3D) structure can achieve rapid nucleation. In addition, the presence of 3D-rGO/SDBS can increase the dissolution and dispersion of gas in solution and further enhance the gas-liquid mass transfer, thus realizing efficient methane storage. The maximum methane storage capacity of 188 v/vw is obtained with 600 ppm of 3D-rGO/SDBS in water, reaching 87% of the theoretical maximum storage capacity. The addition of 3D-rGO/SDBS also significantly reduces the induction time and accelerates the formation rate of methane hydrate. This study reveals that 3D graphene materials have excellent kinetic promotion effects on methane hydrate formation, explores and enriches the hydrate-promoting mechanism, and provides essential data and theoretical basis for the research of new promoters in the field of SNG technology.

Sandwich-like cobalt/reduced graphene oxide/cobalt composite structure presenting synergetic electromagnetic loss effect.

The poor dispersity and oxidation resistance of ferromagnetic metal nanoparticles can induce serious deterioration in electromagnetic properties, which then significantly limits the application of this catalog of materials. In this work, sandwich-like Co/rGo/Co composites were in situ constructed, in which monodispersed Co nanoparticles with diameters of 20-60 nm were densely dispersed on both sides of rGO nanosheets. A connecting network between the densely-packed Co nanoparticles can be formed, where Co nanoparticles are abutted or bridged to each other through a neck of Co. These sandwich-like composites evidently contributed to improved permittivity and permeability, which was ascribed to the enhanced interface polarization and exchange coupling in this Co nanoparticles densely-packed structure. A maximum reflection loss (RLmax) of -61 dB (at 11.1 GHz) together with an efficient absorbing bandwidth (RL < -10 dB, ERL10) of 4 GHz was obtained at a very thin matching thickness of 2 mm. The coating also presented a potential double-band absorbing performance, at SC band and Ku band, respectively. The excellent electromagnetic absorbing performances were ascribed to the synergistic effect of multiple dielectric losses and ferromagnetic losses. The sandwich-like Co/rGO/Co composites proposed an alternative way for broadband and high-efficiency absorption and provided a typical structure to analyze the loss mechanisms.

Construction of ultrathin MnO2 decorated graphene/carbon nanotube nanocomposites as efficient sulfur hosts for high-performance lithium-sulfur batteries.

Lithium-sulfur batteries are attracting significant attention due to their high theoretical specific capacity and low cost. However, their applications are hindered by the poor conductivity of sulfur and capacity fading caused by the shuttle effect. Here, ultrathin manganese dioxide decorated graphene/carbon nanotube nanocomposites are designed as sulfur hosts to suppress the shuttle effect and improve the adsorption efficiency of polysulfides. The graphene/carbon nanotube hybrids, with extraordinary conductivity and large surface area, function as excellent channels for electron transfer and lithium ion diffusion. The ultrathin manganese dioxide nanosheets enable efficient chemical interaction with polysulfides and promote the redox kinetics of polysulfides. As a result, an ultrathin manganese dioxide decorated graphene/carbon nanotube sulfur composite with high sulfur content (81.8 wt%) delivers a high initial specific capacity of 1015.1 mA h g-1 at a current density of 0.1C, high coulombic efficiency approaching 100% and high capacity retention of 84.1% after 100 cycles. The nanocomposites developed in this work have promising applications in high-performance lithium-sulfur batteries.

Rational Construction of Uniform CoNi-Based Core-Shell Microspheres with Tunable Electromagnetic Wave Absorption Properties.

Core-shell particles with integration of ferromagnetic core and dielectric shell are attracting extensive attention for promising microwave absorption applications. In this work, CoNi microspheres with conical bulges were synthesized by a simple and scalable liquid-phase reduction method. Subsequent coating of dielectric materials was conducted to acquire core-shell structured CoNi@TiO2 composite particles, in which the thickness of TiO2 is about 40 nm. The coating of TiO2 enables the absorption band of CoNi to effectively shift from Ku to S band, and endows CoNi@TiO2 microspheres with outstanding electromagnetic wave absorption performance along with a maximum reflection loss of 76.6 dB at 3.3 GHz, much better than that of bare CoNi microspheres (54.4 dB at 17.8 GHz). The enhanced EMA performance is attributed to the unique core-shell structures, which can induce dipole polarization and interfacial polarization, and tune the dielectric properties to achieve good impedance matching. Impressively, TiO2 coating endows the composites with better microwave absorption capability than CoNi@SiO2 microspheres. Compared with SiO2, TiO2 dielectric shells could protect CoNi microspheres from merger and agglomeration during annealed. These results indicate that CoNi@TiO2 core-shell microspheres can serve as high-performance absorbers for electromagnetic wave absorbing application.

Fluorinated graphene/sulfur hybrid cathode for high energy and high power density lithium primary batteries.

It is a great challenge to obtain high performance carbon fluoride (CF x ) cathodes with high specific capacity and good rate performance due to the electronic conductivity of CF x being known to decrease with an increase in the specific capacity. Herein, we propose a novel fluorinated graphene (FG)/sulfur hybrid cathode to enhance both the energy density and power density of lithium/carbon fluoride (Li/CF x ) batteries. Impressive enhancements of the specific capacity, discharge voltage, and rate capability are demonstrated with the novel FG/sulfur hybrid cathode. In comparison with the pristine FG cathode, the hybrid cathode exhibits higher electrochemical activity, lower overpotential, and faster ion transfer over the main discharge range. Furthermore, when the melt-diffusion method is used to prepare the hybrid cathode, the uncommon monoclinic sulfur is presented under ambient temperature. A significant synergistic effect which reduces the reaction resistance effectively is demonstrated with the presence of monoclinic sulfur, leading to the highest energy density of 2341 W h kg-1 and a power density up to 13 621 W kg-1 at 8.0 A g-1. Our results are expected to introduce a new generation of high energy and high power density lithium primary cells, based on a simple and effective strategy employing FG/S hybrid cathodes.

Electromagnetic Wave Absorption Property of Graphene with FeO4 Nanoparticles.

Nanomaterials consisting of various ratios of Fe3O4 and graphene (defined C-Fe3O4/GR) were pre- pared by an in situ coordination complex hydro-thermal synthesis method. The structure and morphology of the nanomaterials C-Fe3O4/GR obtained were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and transmission electron microscopy (TEM). It was found that the Fe3O4 nanoparticles distributed on the surfaces of graphene, and had a spinel structure and a uniform chemical phase when the weight ratios of Fe3O4 to graphene oxide (GO) were 9:1 or 9:2. It was suggested that GO had been successfully reduced to graphene and the Fe3O4 nanoparticles were chemically bonded to graphene. The SQUID vibrating sample magnetometer (SQUID-VSM) indicated that the maximum of the saturation magnetization was 83.6 emmicro g(-1) when the mass ratio of Fe3O4 to GO was 9:2. Electromagnetic wave absorption showed that the chemical compound of Fe3O4 and graphene had a better electromagnetic property than the mechanical blend of Fe3O4 and graphene (M-Fe3O4/GR). The C-Fe3O4/GR had a reflection loss larger than -10 dB in the frequency range 12.9-17.0 GHz for an absorber thickness of 3 mm, and a maximum reflection loss of -12.3 dB at 14.8 GHz and a maximum reflection loss of -31.2 dB at 10.5 GHz for an absorber thickness of 10 mm. Theoretical analysis showed that the electromagnetic wave absorption behavior obeyed the quarter-wave principles. These results showed that the C-Fe3O4/GR nanomaterials can meet the requirements for some engineering applications, showing great application potential in electromagnetic wave absorption.