• YIFU ZHANG

Articles written in Bulletin of Materials Science

• 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 60–150 nm and thickness of about 5–10 nm, while the as-prepared VO2(B) nanobelts have a length of about 1.0–2.7 𝜇m, width, 80–140 nm and thickness, 2–8 nm. 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, energydispersive 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 1000 °C for 2 h. The specific surface area, average pore size and measured pore volume of VC@C were 135.46 m2/g, 4.443 nm and 0.180 cm3/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 thermogravimetric/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.

• Facile synthesis and characterization of rough surface V$_2$O$_5$ nanomaterials for pseudo-supercapacitor electrode material with high capacitance

V$_2$O$_5$ nanomaterials with rough surface were synthesized using commercial V$_2$O$_5$, ethanol (EtOH) and H$_2$O as the starting materials by a simple hydrothermal route and combination of calcination. The electrochemical properties ofV$_2$O$_5$ nanomaterials as electrodes in a supercapacitor device were measured using cyclic voltammetry (CV) and galvanostatic charge–discharge (GCD) method. V$_2$O$_5$ nanomaterials exhibit the specific capacitance of 423 F g$^{−1}$ at the current density of 0.5 A g$^{−1}$ and retain 327 F g$^{−1}$ even at the high current density of 10 A g$^{−1}$. The influence of the ratio of EtOH/H$_2$O, the calcined time and temperature on the morphology, purity and electrochemical property of the products is discussed in detail. The results revealed that the ratio of EtOH/H$_2$O $=$ 10/25 and calcination at 400$^{\circ}$C for 2–4 h are favourable for preparing V$_2$O$_5$ nanomaterials and they exhibited the best electrochemical property. The novel morphology and high specific surface area are the main factors that contribute to high electrochemical performance of V$_2$O$_5$ nanomaterials during the charge–discharge processes. It turns out that V$_2$O$_5$ nanomaterials with rough surface is an ideal material for supercapacitor electrode in the present work.

• Influence of the electrochemical properties of vanadium oxides on specific capacitance by molybdenum doping

Molybdenum (Mo)-doped vanadium dioxide (VO$_2$(B)) nanobelts were successfully synthesized using commercial vanadium pentoxide (V$_2$O$_5$) as the starting material and ammonium molybdate as the dopant by a simple hydrothermal route. Then, Mo-doped VO2(B) nanobelts were transformed to Mo-doped V$_2$O$_5$ nanobelts by calcination at 400$^{\circ}$C under an air atmosphere. The samples were characterized by X-ray powder diffraction,energy-dispersive X-ray spectrometer, elemental mapping, X-ray photoelectron spectroscopy, X-ray fluorescence and transmission electron microscopy techniques. The results showed that Mo-doped VO$_2$(B) and V$_2$O$_5$ solid solution with high purity were obtained. The electrochemical properties of Mo-doped VO$_2$(B) and V$_2$O$_5$ nanobelts as supercapacitor electrodes were measured using cyclic voltammetry (CV) and galvanostatic charge–discharge (GCD). The specific capacitance of VO$_2$(B) nanobelts slightly declines with Mo doping, however, the specific capacitance of V$_2$O$_5$ nanobelts greatly improves with Mo doping. Mo-doped V$_2$O$_5$ nanobelts exhibit the specific capacitance as high as 526 F g$^{−1}$ at the current density of 1 A g$^{−1}$. Both CV and GCD curves show that they have good rate capability and retain 464, 380, 324 and 273 F g$^{−1}$ even at a high-current density of 2, 5, 10 and 20 A g$^{−1}$, respectively. It turns out that Mo-dopedV$_2$O$_5$ nanobelts are ideal materials for supercapacitor electrodes in the present work.

• # Bulletin of Materials Science

Volume 45, 2022
All articles
Continuous Article Publishing mode

• # Dr Shanti Swarup Bhatnagar for Science and Technology

Posted on October 12, 2020

Prof. Subi Jacob George — Jawaharlal Nehru Centre for Advanced Scientific Research, Jakkur, Bengaluru
Chemical Sciences 2020