Tingkai Zhao

Electromagnetic wave absorbing properties of amorphous carbon nanotubes.

Amorphous carbon nanotubes (ACNTs) with diameters in the range of 7–50 nm were used as absorber materials for electromagnetic waves. The electromagnetic wave absorbing composite films were prepared by a dip-coating method using a uniform mixture of rare earth lanthanum nitrate doped ACNTs and polyvinyl chloride (PVC). The microstructures of ACNTs and ACNT/PVC composites were characterized using transmission electron microscope and X-ray diffraction, and their electromagnetic wave absorbing properties were measured using a vector-network analyzer. The experimental results indicated that the electromagnetic wave absorbing properties of ACNTs are superior to multi-walled CNTs, and greatly improved by doping 6 wt% lanthanum nitrate. The reflection loss (R) value of a lanthanum nitrate doped ACNT/PVC composite was −25.02 dB at 14.44 GHz, and the frequency bandwidth corresponding to the reflector loss at −10 dB was up to 5.8 GHz within the frequency range of 2–18 GHz.

A three-dimensional MnO2/graphene hybrid as a binder-free supercapacitor electrode

Highly aligned manganese dioxide (MnO2) nanowall arrays electrodeposited onto Ti sheets are used as substrates to grow graphene (GR) through chemical vapor deposition (CVD), thus forming a three-dimensional (3D) MnO2/GR hybrid composite. Furthermore, a 3D MnO2/GR hybrid with different structures and properties has been prepared at different temperatures. The as-prepared hybrid materials could be directly used as supercapacitor electrodes without any binder and conductive additive, and fully maintain the high conductivity and high specific area of GR, and large pseudocapacitance of MnO2 nanowall arrays. In aqueous electrolytes, the hybrids show a high specific capacitance of ∼326.33 F g−1 with good cycling stability at the scan rate of 200 mV s−1 and high energy density of 23.68 W h kg−1 while maintaining high power density of 7270 W kg−1. The preparation method provides a novel method to fabricate 3D graphene-based composite materials, and the as obtained hybrid electrode demonstrates its potential applications in supercapacitors.

Microwave absorption properties of rare metal-doped multi-walled carbon nanotube/polyvinyl chloride composites

Using rare metal nitrate-doped multi-walled carbon nanotubes as the absorber and polyvinyl chloride as the matrix, the microwave electromagnetic and absorbing properties of multi-walled carbon nanotube/polyvinyl chloride composites were studied. The complex permittivity of the composites doped with different rare metal nitrate decreased in the frequency region of 8.2–12.4 GHz. The minimum reflection loss of rare metal nitrate-doped multi-walled carbon nanotube/polyvinyl chloride composites decreased and shifted slightly to the higher frequency region, and the absorption bandwidth (<−10 dB or >90%) increased in the frequency range of 8–18 GHz compared to multi-walled carbon nanotube/polyvinyl chloride composites. The reflection loss (<−10 dB) of 0.2 wt% La(NO3)3-doped multi-walled carbon nanotube/polyvinyl chloride composites is the widest from the absorption bandwidth (maximum is 5.12 GHz).

Expanded graphite embedded with aluminum nanoparticles as superior thermal conductivity anodes for high-performance lithium-ion batteries

The development of high capacity and long-life lithium-ion batteries is a long-term pursuing and under a close scrutiny. Most of the researches have been focused on exploring electrode materials and structures with high store capability of lithium ions and at the same time with a good electrical conductivity. Thermal conductivity of an electrode material will also have significant impacts on boosting battery capacity and prolonging battery lifetime, which is, however, underestimated. Here, we present the development of an expanded graphite embedded with Al metal nanoparticles (EG-MNPs-Al) synthesized by an oxidation-expansion process. The synthesized EG-MNPs-Al material exhibited a typical hierarchical structure with embedded Al metal nanoparticles into the interspaces of expanded graphite. The parallel thermal conductivity was up to 11.6 W·m−1·K−1 with a bulk density of 453 kg·m−3 at room temperature, a 150% improvement compared to expanded graphite (4.6 W·m−1·K−1) owing to the existence of Al metal nanoparticles. The first reversible capacity of EG-MNPs-Al as anode material for lithium ion battery was 480 mAh·g−1 at a current density of 100 mA·g−1, and retained 84% capacity after 300 cycles. The improved cycling stability and system security of lithium ion batteries is attributed to the excellent thermal conductivity of the EG-MNPs-Al anodes.

Three-Dimensional Graphene/MnO2 Nanowalls Hybrid for High-Efficiency Electrochemical Supercapacitors

In this paper, a facile method is designed to fabricate three-dimensional (3D) graphene (GR)/manganese dioxide (MnO2) nanowall electrode material. The 3D GR/MnO2 hybrid is prepared by a combination...

Hydrogen Storage Behavior of Amorphous Carbon Nanotubes at Low Pressure and Room Temperature

Amorphous carbon nanotubes (ACNTs) were produced by a temperature-controlled arc discharging furnace with a mixture powders of Co-Ni (1:1wt%) alloy as catalyst and hydrogen as buffer gas. As-grown and treated ACNTs with a mean diameter of about 14nm for hydrogen storage and release experiments were studied in this paper. The test experiments of hydrogen uptake and release were carried out by a volumetric gas-adsorption measurement system. The results indicated that the hydrogen storage capacity of ACNTs was 1.1wt% at the pressure of 2.45MPa and room temperature. Around 50% of the adsorbed hydrogen gas of ACNTs could be released under a standard pressure and at room temperature.

Hydrogen storage capacity of single-walled carbon nanotube prepared by a modified arc discharge

ABSTRACT Single-walled carbon nanotubes (SWCNTs, the mean diameter of 1.35 nm) were produced by a modified arc discharging furnace using a mixture powder of KCl and Co-Ni alloy as catalyst at 600°C. The hydrogen storage capacity of SWCNTs was enhanced by the mechanism of atom hydrogen spillover from the supported catalyst. The temperature effect on the hydrogen storage capacity of as-grown SWCNTs was investigated. The relative experiments of SWCNT hydrogen uptake and release were carried out by a high-pressure volumetric gas-adsorption measurement system. The experimental results indicated that the hydrogen storage capacity of SWCNTs increased with the environmental temperatures decreasing. The hydrogen storage capacity of SWCNTs was up to 1.73 wt% at 77 K for 2 hours under the pressure of 10 MPa, and the corresponding releasing hydrogen capacity is about 1.23 wt% under ambient pressure.

Preparations and Properties of Porous Copper Materials for Lithium-Ion Battery Applications

Because of its special porous structure and novel physical and mechanical properties, porous copper is widely studied in many fields, especially in high-performance lithium-ion batteries. It is quite necessary for researchers to understand the recent progress of porous copper. Herein, we review the preparations, properties, and lithium-ion battery (LIB) applications of porous copper. Its main research direction and development trend are also pointed.

Electrochemical Property of Multi-Walled Carbon Nanotubes/Chitosan Composites by Electrostatic Interactions

Biocompatible multi-walled carbon nanotubes (MWCNTs)/chitosan(CS) composites were synthesized by electrostatic interactions between positively charged CS and negatively charged MWCNTs colloid solution functionalized with nitric and sulfate acid. The effect of pH value on the viscosity of MWCNTs/CS colloid could be controlled by adjusting the pH value, which was determined by the charge type and potential strength. The electrochemical properties of MWCNTs/CS composites were also studied by CHI650C electrochemical workstation. The MWCNTs/CS composites were characterized by using Fourier transform infrared spectrometer (FT-IR), High-Resolution Transmission Electron Microscope (HRTEM) and thermal gravimetric analysis (TGA). The experimental results showed that the stable and homogeneous MWCNTs/CS composites were obtained at pH 5 owing to existing strong electrostatic attraction. The weight ratio of CS polymer attached on the surface of MWCNTs was around 45wt%, and the thickness of CS grafted on the surface of MWCNTs was about 4nm. The electrocatalytic activity of nitrite (NO2 −) decorated with MWCNTs/CS composites glass-carbon electrode was tested, and the results indicated that the MWCNTs/CS modified electrode possess excellent electrocatalytic ability.

Physical model for the growth of amorphous carbon nanotubes

A physical model for the growth mechanism of amorphous carbon nanotubes (ACNTs) (namely, “open tips growth and carbon clusters (Cn,n>6) adding”) has been proposed in this letter. Based on Tersoff–Brenner [Phys. Rev. B 37, 6991 (1988) and Phys. Rev. B 42, 9458 (1990)] and Lennard-Jones potential energy functions, a mathematic relationship for the growth of ACNTs was established. The predicted diameters of ACNTs from this physical model were in the range of 5–25 nm. The predicted values were in agreement with the experimental measurements in the range of 7–20 nm.