Yifu Zhang

Controlled synthesis and electrochemical properties of vanadium oxides with different nanostructures

Vanadium oxides (V3O7·H2O and VO2) with different morphologies have been selectively synthesized by a facile hydrothermal approach using glucose as the reducing and structure-directing reagent. The as-obtained V3O7·H2O nanobelts have a length up to several tens of micrometers, width of about 60–150xa0nm and thickness of about 5–10xa0nm, while the as-prepared VO2(B) nanobelts have a length of about 1·0–2·7xa0μm, width, 80–140xa0nm and thickness, 2–8xa0nm. It was found that the quantity of glucose, the reaction temperature and the reaction time had significant influence on the compositions and morphologies of final products. Vanadium oxides with different morphologies were easily synthesized by controlling the concentration of glucose. The formation mechanism was also briefly discussed, indicating that glucose played different roles in synthesizing various vanadium oxides. The phase transition from VO2(B) to VO2(M) were investigated and the phase transition temperature of the VO2(M) appeared at around 68 °C. Furthermore, the electrochemical properties of V3O7·H2O nanobelts, VO2(B) nanobelts and VO2(B) nanosheets were investigated and they exhibited a high initial discharge capacity of 296, 247 and 227 mAh/g, respectively.

Exploring a novel approach to fabricate vanadium carbide encapsulated into carbon nanotube (VC@C) with large specific surface area

A novel approach to the fabrication of vanadium carbide encapsulated into carbon nanotube (VC@C) core-shell structured composite by thermal treatment with the precursor V3O7·H2O@C was developed for the first time. The as-obtained VC@C were characterized by X-ray powder diffraction (XRD), Raman spectrum, energy-dispersive X-ray spectrometer (EDX), elemental analysis (EA), Fourier transform infrared spectroscopy (FT)–(IR), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Brunauer–Emmett–Teller (BET). The results showed that VC@C with core-shell structures could be successfully synthesized at 1000xa0°C for 2xa0h. The specific surface area, average pore size and measured pore volume of VC@C were 135·46xa0m2/g, 4·443xa0nm and 0·180xa0cm3/g, respectively indicating that the as-obtained VC@C composite could be used as a mesoporous material. Furthermore, thermal behaviour of the as-obtained VC@C composite in air was investigated by thermo-gravimetric/differential thermal analyser (TG/DTA). The experimental result revealed that the carbon coated on the surface of VC has high activity with O2 in air atmosphere.

Designed synthesis of tunable amorphous carbon nanotubes (a-CNTs) by a novel route and their oxidation resistance properties

Tunable amorphous carbon nanotubes (a-CNTs) were successfully synthesized using V3O7·H2O and glucose solution as the starting materials by a novel route for the first time. The as-obtained samples were separately characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray powder diffraction (XRD), energy-dispersive spectrometer (EDS), elemental analysis (EA), Fourier transform infrared spectroscopy (FT-IR) and Raman spectrum. The results showed that the as-obtained a-CNTs had uniform diameters with outer diameter ranging from 140 to 250 nm and inner diameter about 28 nm on an average, and their length was up to several micrometres. No VOx residues remaining in a-CNTs showed the as-obtained a-CNTs with high purity. The as-prepared a-CNTs were a kind of hydrogenated a-CNTs containing both the sp3- and sp2-type carbons. Furthermore, the thermal stability of the as-obtained a-CNTs in the air atmosphere were investigated by thermo-gravimetric/differential thermal analyser (TG-DTA), revealing that the as-obtained a-CNTs had good thermal stability and oxidation resistance below 300 °C in air.