Preparation and capacitance properties of Ni foam@graphene@Co_(3)O_(4)composite electrode materials

Graphene under high temperature was prepared and loaded on Ni foam.Then,cobalt tetroxide precursor was grown on Ni foam in situ by the hydrothermal method.Finally,the sample was burned at high temperature to obtain Co_(3)O_(4)+graphene@Ni.The hydrothermal method used in this paper is easy to operate,with low-risk factors and environmental protection.The prepared Co_(3)O_(4)+graphene@Ni electrode exhibits superior electrochemical performance than Co_(3)O_(4)@Ni electrode.At a current density of 1 A/g,the specific capacitance of the Co_(3)O_(4)+graphene@Ni electrode calculated by a charge-discharge test is 935 F/g,which is much larger than that of Co_(3)O_(4)@Ni electrode of 340 F/g.

Synthesis and characterization of Co_3O_4 prepared from atmospheric pressure acid leach liquors of nickel laterite ores

A chemical precipitation-thermal decomposition method was developed to synthesize Co3O4 nanoparticles using cobalt liquor obtained from the atmospheric pressure acid leaching process of nickel laterite ores. The effects of the precursor reaction temperature, the concentration of Co2＋, and the calcination temperature on the specific surface area, morphology, and the electrochemical behavior of the ob- tained Co304 particles were investigated. The precursor basic cobaltous carbonate and cobaltosic oxide products were characterized and ana- lyzed by Fourier transform infrared spectroscopy, thermogravimetric differential thermal analysis, X-ray diffraction, field-emission scanning electron microscopy, specific surface area analysis, and electrochemical analysis. The results indicate that the specific surface area of the Co3O4particles with a diameter of 30 rim, which were obtained under the optimum conditions of a precursor reaction temperature of 30℃, 0.25 mol/L Co2＋, and a calcination temperature of 350℃, was 48.89 m2/g. Electrodes fabricated using Co3O4 nanoparticles exhibited good electrochemical properties, with a specific capacitance of 216.3 F/g at a scan rate of 100 mV/s.

Investigation on the broadband electromagnetic wave absorption properties and mechanism of Co3O4- nanosheets/reduced-graphene-oxide composite

A cobaltosic-oxide-nanosheets/reduced-graphene-oxide composite （CoNSs@RGO） was successfully prepared as a light-weight broadband electromagnetic wave absorber. The effects of the sample thickness and amount of composite added to paraffin samples on the absorption properties were thoroughly investigated. Due to the nanosheet-like structure of Co3O4, the surface-to-volume ratio of the wave absorption material was very high, resulting in a large enhancement in the absorption properties. The maximum refection loss of the CoNSs@RGO composite was -45.15 dB for a thickness of 3.6 mm, and the best absorption bandwidth with a reflection loss below -10 dB was 7.14 GHz with a thickness of 2.9 mm. In addition, the peaks of microwave absorption shifted towards the low frequency region with increasing thickness of the absorbing coatings. The mechanism of electromagnetic wave absorption was attributed to impedance matching of CoNSs@RGO as well as the dielectric relaxation and polarization of RGO. Compared to previously reported absorbing materials, CoNSs@RGO showed better performance as a lightweight and highly efficient absorbing material for application in the high frequency band.

Novel porous starfish-like Co3O4@nitrogen-doped carbon as an advanced anode for lithium-ion batteries

A Co-based metal-organic framework （Co-MOF） with a unique three-dimensional starfish-like nanostructure was successfully synthesized using a simple ultrasonic method. After subsequent carbonization and oxidation, a nanocomposite of nitrogen-doped carbon with a Co3O4 coating （Co3O4@N-C） with a porous starfish-like nanostructure was obtained. The final hybrid exhibited excellent lithium storage performance when evaluated as an anode material in a lithiumion battery. A remarkable and stable discharge capacity of 795 mAh·g^-1 was maintained at 0.5 A·g^-1 after 300 cycles. Excellent rate capability was also obtained. In addition, a full Co3O4@N-C/LiFePO4 battery displayed stable capacity retention of 95% after 100 cycles. This excellent lithium storage performance is attributed to the unique porous starfish-like structure, which effectively buffers the volume expansion that occurs during Li^＋ insertion/deinsertion. Meanwhile, the nitrogendoped carbon coating enhances the electrical conductivity and provides a buffer layer to accommodate the volume change and accelerate the formation of a stable solid electrolyte interface layer.