Mao-Zhang Wang

Adsorption and capillarity of nitrogen in aggregated multi-walled carbon nanotubes

Abstract Pores in aggregated multi-walled carbon nanotubes (MWNTs) can be mainly divided into inner hollow cavities of smaller diameter (narrowly distributed, mainly 3.0–4.0 nm) and aggregated pores (widely distributed, 20–40 nm), formed by the interaction of isolated MWNTs. The two types of pores shall, respectively, determine nitrogen cryogenic capillarity process under different pressures. It is worth to note that ultra-strong nitrogen capillarity in the aggregated pores ( 590 mg N 2 / g ) contributes to the 78.5% of the total adsorption amount (up to 750 mg/g near to the ambient pressure), showing that the aggregated pores of the MWNTs are much more important than their inner cavities for adsorption and capillarity in some cases.

Macroporous ‘bubble’ graphene film via template-directed ordered-assembly for high rate supercapacitors

A three-dimensional bubble graphene film, with controllable and uniform macropores and tailorable microstructure, was fabricated by a facile hard templating strategy and exhibit extraordinary electrochemical capacitance with high rate capability (1.0 V s(-1)).

Chemically derived graphene-metal oxide hybrids as electrodes for electrochemical energy storage: pre-graphenization or post-graphenization?

The introduction of a secondary phase is an efficient and effective way to improve the electrochemical performance of graphene towards energy storage applications. Two fundamental strategies including pre-graphenization and post-graphenization were widely employed for graphene-based hybrids. However, there is still an open question of which way is better. In this contribution, we investigated the differences in the structure and electrochemical properties of pre- and post-graphenized graphene-SnO2 hybrids. The pre-graphenization is realized by synthesis of thermally reduced graphene and subsequent impregnation of SnO2, while the post-graphenization is realized by introducing a Sn-containing phase onto GO sheets followed by chemical reduction. The pre-graphenization process provides a large amount of pores for ion diffusion, which is of benefit for loading of SnO2, fast ion diffusion for supercapacitors, and higher capacity for Li-ion batteries, but poor stability, while the post-graphenization process offers compact graphene and good interaction between the SnO2 and graphene, which provides stable structure for long term stability for supercapacitor and Li-ion battery use.

Crumpled reduced graphene oxide by flame-induced reduction of graphite oxide for supercapacitive energy storage

A novel flame-induced synthesis approach was developed to prepare crumpled reduced graphene oxide (rGO) from graphite oxide (GO) powder with the assist of flammable polar solvents such as methanol, ethanol and acetone under ordinary conditions. The as-prepared methanol–rGO, ethanol–rGO and acetone–rGO exhibit a high surface area of 421, 500 and 384 m2 g−1, respectively. The method is highly attractive for the mass production of graphene due to its simplicity, high efficiency, energy saving property and cost-effectiveness. The thermal exfoliation and reduction of GO powder, as well as the morphology and surface chemistry of resulting rGO, were related to the volatility, infiltration and combustion heat of the solvents. The electrochemical properties of the rGO samples were further evaluated in a 6 M KOH aqueous electrolyte. In a three-electrode setup, the corresponding specific capacitance of methanol–rGO, ethanol–rGO and acetone–rGO was calculated to be 260, 221 and 200 F g−1 at a current density of 0.1 A g−1, respectively. Moreover, the flame-reduced methanol–rGO exhibited a maximum energy density of 68.85 W h kg−1 as tested in a two-electrode system. The excellent supercapacitive performance of the methanol–rGO and ethanol–rGO materials is attributable to the combination of high surface area, residual oxygen containing groups and wrinkled morphologies.

Preparation and characterization of silicon carbide fibers from activated carbon fibers

Silicon carbide fibers were prepared by the reaction between activated carbon fibers and silicon monoxide generated from a mixture of silicon and silicon dioxide at temperatures from 1200 to 1300°C in an inert atmosphere of argon. The reaction was completed at temperatures as low as 1200°C, which means that activated carbon fibers had a high reactivity. The resulting sample maintained the original morphology of the starting material, which was an advantage because of the difficulty in post shaping silicon carbide, and led to a silicon carbide fiber with high specific surface area. The resulting samples were characterized by powder X-ray diffraction, thermal gravimetric analysis, and by nitrogen adsorption measurements at 77.4 K to obtain surface area and pore size distributions. The morphology of the resulting sample was observed by scanning electron microscopy and the electronic structure was investigated by Fourier transformation infrared spectroscopy and X-ray photoelectron spectroscopy techniques.