Peng-Xiang Hou

Low-Temperature Exfoliated Graphenes: Vacuum-Promoted Exfoliation and Electrochemical Energy Storage

A preheated high-temperature environment is believed to be critical for a chemical-exfoliation-based production of graphenes starting from graphite oxide, a belief that is based on not only experimental but also theoretical viewpoints. A novel exfoliation approach is reported in this study, and the exfoliation process is realized at a very low temperature, which is far below the proposed critical exfoliation temperature, by introducing a high vacuum to the exfoliation process. Owing to unique surface chemistry, low-temperature exfoliated graphenes demonstrate an excellent energy storage performance, and the electrochemical capacitance is much higher than that of the high-temperature exfoliated ones. The low-temperature exfoliation approach presents us with a possibility for a mass production of graphenes at low cost and great potentials in energy storage applications of graphene-based materials.

Multi-step purification of carbon nanotubes

An efficient purification procedure for multi-walled carbon nanotubes (MWNTs) synthesized by the floating catalyst method was discussed. The process involves ultra-sonication, heat treatment in hot water, bromination, oxidation and acid treatment. Most of amorphous carbon, multishell carbon nanocapsules as well as metal particles were successfully removed from the MWNT product. With this procedure, MWNTs with purity of more than 94% were obtained and the yield could approach 50%. It was found that bromination took an important role in the purification of MWNTs. Transmission electron microscopy, XPS and thermo-gravimetric analysis were used to evaluate the purification process of MWNTs. The mechanism of bromination on purification of the MWNTs was also discussed

3D Interconnected Electrode Materials with Ultrahigh Areal Sulfur Loading for Li–S Batteries

Sulfur electrodes based on a 3D integrated hollow carbon fiber foam (HCFF) are synthesized with high sulfur loadings of 6.2-21.2 mg cm(-2) . Benefiting from the high electrolyte absorbability of the HCFF and the multiple conductive channels, the obtained electrode demonstrates excellent cycling stability and a high areal capacity of 23.32 mAh cm(-2) , showing great promise in commercially viable Li-S batteries.

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.

Fabrication of nano-Al based composites reinforced by single-walled carbon nanotubes

Chinese Acad Sci, Met Res Inst, Shenyang Natl Lab Mat Sci, Shenyang 110016, Peoples R China.;Cong, HT (reprint author), Chinese Acad Sci, Met Res Inst, Shenyang Natl Lab Mat Sci, Shenyang 110016, Peoples R China;htcong@imr.ac.cn

Investigation of the ion storage/transfer behavior in an electrical double-layer capacitor by using ordered microporous carbons as model materials.

An ordered microporous carbon, which was prepared with zeolite as a template, was used as a model material to understand the ion storage/transfer behavior in electrical double-layer capacitor (EDLC). Several types of such zeolite-templated carbons (ZTCs) with different structures (framework regularity, particle size and pore diameter) were prepared and their EDLC performances were evaluated in an organic electrolyte solution (1 M Et(4)NBF(4)/propylene carbonate). Moreover, a simple method to evaluate a degree of wettability of microporous carbon with propylene carbonate was developed. It was found that the capacitance was almost proportional to the surface area and this linearity was retained even for the carbons with very high surface areas (>2000 m(2) g(-1)). It has often been pointed out that thin pore walls limit capacitance and this usually gives rise to the deviation from linearity, but such a limitation was not observed in ZTCs, despite their very thin pore walls (a single graphene, ca. 0.34 nm). The present study clearly indicates that three-dimensionally connected and regularly arranged micropores were very effective at reducing ion-transfer resistance. Despite relatively small pore diameter ZTCs (ca. 1.2 nm), their power density remained almost unchanged even though the particle size was increased up to several microns. However, when the pore diameter became smaller than 1.2 nm, the power density was decreased due to the difficulty of smooth ion-transfer in such small micropores.

A nanosized Fe2O3 decorated single-walled carbon nanotube membrane as a high-performance flexible anode for lithium ion batteries

An Fe2O3/single-walled carbon nanotube (Fe2O3/SWCNT) membrane with high Fe2O3 loading (88.0 wt%) is prepared by oxidizing a flow-assembled Fe/SWCNT membrane. The Fe2O3/SWCNT membrane can be used as a flexible, binder-free and current-collector-free anode in lithium ion batteries, which shows a high reversible capacity of 1243 mA h g−1 at a current density of 50 mA g−1 and an excellent cyclic stability over 90 cycles at 500 mA g−1. The superior electrochemical performance of the Fe2O3/SWCNT electrode can be attributed to the structural characteristics of the SWCNT network and the uniformly distributed Fe2O3 nanoparticles (5–10 nm). The nanosized Fe2O3 has a short lithium ion diffusion length and minimal volume change during lithiation–delithiation. The high loading ratio of Fe2O3 nanoparticles renders the high capacity. The highly conducting interwoven SWCNT network not only facilitates electron conduction but also buffers the strain applied to Fe2O3 nanoparticles during the lithiation and delithiation. These results demonstrate the great potential of this hybrid membrane anode for high-performance flexible lithium ion batteries.

Improved electrochemical performance of Fe2O3 nanoparticles confined in carbon nanotubes

A hybrid material of carbon nanotube (CNT)-encapsulated Fe2O3 nanoparticles was prepared by immersing CNTs with two open ends in a Fe(NO3)3 solution followed by thermal decomposition. It was found that the hollow core of the CNTs was filled with a homogeneous array of Fe2O3 nanoparticles with each nanoparticle being a single crystal. As an anode material of lithium-ion batteries, the Fe2O3-filled CNTs exhibited an improved electrochemical performance in terms of high reversible capacity, excellent cycling stability (811.4 mA h g−1 after 100 cycles), and high rate capability, compared to that of pure Fe2O3. We attribute this superior electrochemical performance of the Fe2O3-filled CNTs to the small size of the Fe2O3 nanoparticles, the confinement effect of CNTs, sound electrical contact between these two components, as well as the good electrical conductivity and unique porous structure of CNTs that improve the electron and lithium ion transport ability of the anode.

Bulk Synthesis of Large Diameter Semiconducting Single-Walled Carbon Nanotubes by Oxygen-Assisted Floating Catalyst Chemical Vapor Deposition

Semiconducting single-walled carbon nanotubes (s-SWCNTs) with a mean diameter of 1.6 nm were synthesized on a large scale by using oxygen-assisted floating catalyst chemical vapor deposition. The oxygen introduced can selectively etch metallic SWCNTs in situ, while the sulfur growth promoter functions in promoting the growth of SWCNTs with a large diameter. The electronic properties of the SWCNTs were characterized by laser Raman spectroscopy, absorption spectroscopy, and field effect transistor measurements. It was found that the content of s-SWCNTs in the samples was highly sensitive to the amount of oxygen introduced. Under optimum synthesis conditions, enriched s-SWCNTs can be obtained in milligram quantities per batch.

Toward More Reliable Lithium-Sulfur Batteries: An All-Graphene Cathode Structure.

Lithium-sulfur (Li-S) batteries are attracting increasing interest due to their high theoretical specific energy density, low cost, and eco-friendliness. However, most reports of the high gravimetric specific capacity and long cyclic life are not practically reliable because of their low areal specific capacity derived from the low areal sulfur loading and low sulfur content. Here, we fabricated a highly porous graphene with high pore volume of 3.51 cm(3) g(-1) as the sulfur host, enabling a high sulfur content of 80 wt %, and based on this, we further proposed an all-graphene structure for the sulfur cathode with highly conductive graphene as the current collector and partially oxygenated graphene as a polysulfide-adsorption layer. This cathode structural design enables a 5 mg cm(-2) sulfur-loaded cathode showing both high initial gravimetric specific capacity (1500 mAh g(-1)) and areal specific capacity (7.5 mAh cm(-2)), together with excellent cycling stability for 400 cycles, indicating great promise for more reliable lithium-sulfur batteries.