Uniform FexNiy nanospheres were synthesized via a simple solvothermal method and used as electrocatalysts for Li–O2 batteries. Fe7Ni3 nanospheres exhibited relatively high catalytic activities in the electrochemical tests. They delivered a reversible capacity of more than 7000 mAh/gKB and gave a discharge–charge voltage gap reduction of 250 mV compared with Ketjen Black.Topics: Batteries; Catalysts; Electric transport processes and properties; Electrochemical analysis; Nanostructures; Phase; Spectra;

Single crystal CoO nanobelts with thicknesses of several nanometers and widths of 30−100 nm and polycrystalline CoO submicrometer spheres self-assembled by nanoparticles with diameters ranging from 20 to 40 nm were synthesized via a microemulsion method under solvothermal conditions. The shape and size of CoO nanostuctures can be well controlled by H2O/surfactant molar ratio and other solvothermal parameters. Apart from structural and morpholoical characterizations of the submicrometer spheres and the nanobelts, powder X-ray diffraction, electron microscopy techniques, and microwave absorption properties of typical samples have also been investigated. The results indicate that the microwave absorption of nanobelts is stronger than that of submicrometer spheres.

•Monodispersed FeNi3 alloy nanocrystals have been successfully assembled on 2D graphene via a one-pot strategy.•The process ensures different crystal phase and controlled morphology and size in the monodispersed particles.•The nanocomposites exhibit excellent microwave absorbability, which is stronger than the corresponding alloy monomer.FeNi3 nanocrystals as an ideal candidate for EM-wave-absorption material have a great advantage due to their excellent magnetic properties. However, its large permittivity and poor chemical stability confine its application. A strategy to improve electromagnetic performance of FeNi3via phase-controlled synthesis of FeNi3 nanostructures grown on graphene networks has been employed in this work. The phases, structures, sizes and morphologies of FeNi3 nanocomposites were in-depth characterized by using scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), powder X-ray diffraction (XRD), Fourier transform infrared spectra (FT-IR), and Raman spectroscopy. The results of electromagnetic performance tests for the as-synthesized FeNi3 nanocomposites showed excellent microwave absorbability in comparison with the corresponding FeNi3 nanocrystals, especially in the low (2–6 GHz) and middle (6–12 GHz) frequencies. The one-pot method we utilized is simple and effective, and because of its versatility, it may be extended to prepare some magnetic metal or alloy materials via this route.

Face-centered cubic α-LiFeO2 and spinel β-LiFe5O8 with uniform size and high dispersion have been successfully assembled on 2D graphene sheets via a facile one-pot strategy under different reaction conditions. The reduction of GO by this method is effective and comparable to conventional methods, which was confirmed by X-ray diffraction (XRD), Fourier transform infrared (FT-IR), Raman spectroscopy and X-ray photoelectron spectroscopy (XPS). The structure of the products can be easily controlled by changing the solvent and reaction temperature. It was shown that the as-formed β-LiFe5O8 and α-LiFeO2 nanocrystals with a diameter of ca. 5 nm and 7 nm, respectively, were densely and uniformly anchored on the graphene sheets, and as a result, the aggregation of the nanoparticles was effectively prevented. The investigation of the microwave absorbability reveals that the α-LiFeO2–GN and β-LiFe5O8–GN nanocomposites exhibit excellent microwave absorbability, which is stronger than that of the corresponding α-LiFeO2 and β-LiFe5O8 nanostructures, respectively.

Cobalt is a promising soft metallic magnetic material used for important applications in the field of absorbing stealth technology, especially for absorbing centimeter waves. However, it frequently presents a weak dielectric property because of its instability, aggregation, and crystallographic form. A method for enhancing the electromagnetic property of metal Co via phase-controlled synthesis of Co nanostructures grown on graphene (GN) networks has been developed. Hexagonal close-packed cobalt (α-Co) nanocrystals and face-centered cubic cobalt (β-Co) nanospheres with uniform size and high dispersion have been successfully assembled on GN nanosheets via a facile one-step solution-phase strategy under different reaction conditions in which the exfoliated graphite oxide (graphene oxide, GO) nanosheets were reduced along with the formation of Co nanocrystals. The as-synthesized Co/GN nanocomposites showed excellent microwave absorbability in comparison with the corresponding Co nanocrystals or GN, especially for the nanocomposites of GN and α-Co nanocrystals (the reflection loss is −47.5 dB at 11.9 GHz), which was probably because of the special electrical properties of the cross-linked GN nanosheets and the perfect electromagnetic match in their microstructure as well as the small particle size of Co nanocrystals. The approach is convenient and effective. Some magnetic metal or alloy materials can also be prepared via this route because of its versatility.Keywords: cobalt; electromagnetic performance; graphene; microwave absorbability; nanostructures;

Hexagonal close-packed Ni (h-Ni) nanocrystals and face-centered cubic Ni (c-Ni) nanoflowers with uniform size and high dispersion have been successfully assembled on graphene nanosheets (GN) via a facile one-step solution-phase strategy under different reaction conditions, where the reduction process of graphite oxide (GO) sheets into GN was accompanied by the generation of Ni nanocrystals. The reduction of GO by this method is effective, which was confirmed by X-ray diffraction (XRD), Fourier transform infrared (FTIR) and Raman spectroscopy and is comparable to conventional methods. The phase and morphology of nickel can be easily tuned by varying the reaction temperature and solvent. It was shown that the as-formed h-Ni nanocrystals with a diameter as small as 3 nm are grown densely and uniformly on the graphene sheets, and as a result the aggregation of the h-Ni nanocrystals was effectively prevented. In addition, c-Ni nanospheres assembled by c-Ni nanocrystals with a size of 15 nm were also uniformly deposited on the graphene sheets. The investigation of the microwave absorbability reveals that the three Ni/GN nanocomposites exhibit excellent microwave absorbability, which is stronger than the corresponding Ni nanostructures.

Iron-based microstructured or nanostructured materials, including Fe, γ-Fe2O3, and Fe3O4, are highly desirable for magnetic applications because of their high magnetization and a wide range of magnetic anisotropy. An important application of these materials is use as an electromagnetic wave absorber to absorb radar waves in the centimeter wave (2−18 GHz). Dendrite-like microstructures were achieved with the phase transformation from dendritic α-Fe2O3 to Fe3O4, Fe by partial and full reduction, and γ-Fe2O3 by a reduction−oxidation process, while still preserving the dendritic morphology. The investigation of the magnetic properties and microwave absorbability reveals that the three hierarchical microstructures are typical ferromagnets and exhibit excellent microwave absorbability. In addition, this also confirms that the microwave absorption properties are ascribed to the dielectric loss for Fe and the combination of dielectric loss and magnetic loss for Fe3O4 and γ-Fe2O3.Keywords (keywords): dendrite-like; magnetic materials; microstructure; microwave-absorbing materials; nanostructure;

Novel hierarchical cobalt phosphate (α- and β-Co2P2O7) and cobalt hydrogen phosphate hydroxide [Co11(HPO3)8(OH)6] three-dimensional (3D) architectures with different morphologies were synthesized under a solvothemal condition. The form and shape of cobalt phosphate can be readily tuned by adjusting experimental parameters of the reaction system. The novel hierarchical α-Co2P2O7 microcrystals with basketry-like microstructures were obtained with a molar ratio of Co2+/H3PO4/CH3NH2/HO(CH2)2OH of 1:1.2:1:108, the reaction temperature of 180 °C, and the reaction time of 5 days; dumbbell-like β-Co2P2O7 microspheres were formed with the same reaction temperature and time but the molar ratio of 1:1.2:1:54, and Co11(HPO3)8(OH)6 with peony-like nanostructures was prepared with the same molar ratio and reaction time as β-Co2P2O7 but the reaction temperature of 120 °C. The samples were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), Fourier transform infrared spectra (FT-IR) technologies, a Quantum Design superconducting quantum interference device (SQUID) magnetometer, and a network analyzer. The formation mechanism of cobalt phosphate microstructures was investigated in detail.

Face-centered cubic α-LiFeO2 and spinel β-LiFe5O8 with uniform size and high dispersion have been successfully assembled on 2D graphene sheets via a facile one-pot strategy under different reaction conditions. The reduction of GO by this method is effective and comparable to conventional methods, which was confirmed by X-ray diffraction (XRD), Fourier transform infrared (FT-IR), Raman spectroscopy and X-ray photoelectron spectroscopy (XPS). The structure of the products can be easily controlled by changing the solvent and reaction temperature. It was shown that the as-formed β-LiFe5O8 and α-LiFeO2 nanocrystals with a diameter of ca. 5 nm and 7 nm, respectively, were densely and uniformly anchored on the graphene sheets, and as a result, the aggregation of the nanoparticles was effectively prevented. The investigation of the microwave absorbability reveals that the α-LiFeO2–GN and β-LiFe5O8–GN nanocomposites exhibit excellent microwave absorbability, which is stronger than that of the corresponding α-LiFeO2 and β-LiFe5O8 nanostructures, respectively.

Hexagonal close-packed Ni (h-Ni) nanocrystals and face-centered cubic Ni (c-Ni) nanoflowers with uniform size and high dispersion have been successfully assembled on graphene nanosheets (GN) via a facile one-step solution-phase strategy under different reaction conditions, where the reduction process of graphite oxide (GO) sheets into GN was accompanied by the generation of Ni nanocrystals. The reduction of GO by this method is effective, which was confirmed by X-ray diffraction (XRD), Fourier transform infrared (FTIR) and Raman spectroscopy and is comparable to conventional methods. The phase and morphology of nickel can be easily tuned by varying the reaction temperature and solvent. It was shown that the as-formed h-Ni nanocrystals with a diameter as small as 3 nm are grown densely and uniformly on the graphene sheets, and as a result the aggregation of the h-Ni nanocrystals was effectively prevented. In addition, c-Ni nanospheres assembled by c-Ni nanocrystals with a size of 15 nm were also uniformly deposited on the graphene sheets. The investigation of the microwave absorbability reveals that the three Ni/GN nanocomposites exhibit excellent microwave absorbability, which is stronger than the corresponding Ni nanostructures.