Shaoming Huang

Sulfur-Doped Graphene as an Efficient Metal-free Cathode Catalyst for Oxygen Reduction

Tailoring the electronic arrangement of graphene by doping is a practical strategy for producing significantly improved materials for the oxygen-reduction reaction (ORR) in fuel cells (FCs). Recent studies have proven that the carbon materials doped with the elements, which have the larger (N) or smaller (P, B) electronegative atoms than carbon such as N-doped carbon nanotubes (CNTs), P-doped graphite layers and B-doped CNTs, have also shown pronounced catalytic activity. Herein, we find that the graphenes doped with the elements, which have the similar electronegativity with carbon such as sulfur and selenium, can also exhibit better catalytic activity than the commercial Pt/C in alkaline media, indicating that these doped graphenes hold great potential for a substitute for Pt-based catalysts in FCs. The experimental results are believed to be significant because they not only give further insight into the ORR mechanism of these metal-free doped carbon materials, but also open a way to fabricate other new low-cost NPMCs with high electrocatalytic activity by a simple, economical, and scalable approach for real FC applications.

Band structure, phonon scattering, and the performance limit of single-walled carbon nanotube transistors.

Semiconducting single-walled carbon nanotubes are studied in the diffusive transport regime. The peak mobility is found to scale with the square of the nanotube diameter and inversely with temperature. The maximum conductance, corrected for the contacts, is linear in the diameter and inverse temperature. These results are in good agreement with theoretical predictions for acoustic phonon scattering in combination with the unusual band structure of nanotubes. These measurements set the upper bound for the performance of nanotube transistors operating in the diffusive regime.

A Lightweight TiO2/Graphene Interlayer, Applied as a Highly Effective Polysulfide Absorbent for Fast, Long‐Life Lithium–Sulfur Batteries

DOI: 10.1002/adma.201405637 using microporous carbon paper and achieved signifi cant improvements not only in the use of the active material but also in the capacity retention. [ 12 ] More recently, various free-standing carbon interlayers including carbonized paper, a carbonized eggshell membrane, and an acetylene black mesh have been developed for the interception of migrating PS ions. [ 13–15 ] Investigating different categories of carbon interlayers has become a major avenue of current research into the insertion of interlayers. Meanwhile, non-carbon interlayers also appeared on stage. A typical example is that the Li + selective permselective membrane based on a coating layer of Nafi on blocks the diffusion of PS anions across the membrane to the Li anode, which greatly suppresses the shuttling of PS. [ 16 ] Since the diffusion of PS was localized on the cathode side, the cycling stability of the Li–S battery can be dramatically improved. Although these carbon and non-carbon interlayers have shown that it is possible to suppress the diffusion of PS and to improve the cycle-ability, some crucial issues remain to be resolved: i) As for these carbon and non-carbon interlayers, the complexity of the processes required for the synthesis of unique interlayers hinders their large-scale application, furthermore, the unsatisfactory thickness/weight of the applied interlayer may lead to a sharp decrease in the overall energy density, which may offset the gains in cell performance; ii) when the carbon interlayer acts only as a physical barrier, its nonpolar nature leads to weak interaction with polar PS anions, greatly reducing their ability to bind and confi ne these species during cycling. Moreover, the Li + ion transfer may be impeded by the physical barrier; iii) with regard to the non-carbon interlayer, a lower initial discharge capacity compared to the counterpart cathode was arisen likely due to increasing the resistance to some extent. To address shuttling of PS issues, the adjustment of the interlayer components may be a desirable strategy; in theory, an ideal interlayer should be able to selectively control the shuttling of PS anions via strong chemical interactions between them, while not disturbing the Li + ion transfer. Developing a lightweight and chemically selective interlayer carbon is therefore seems to be urgent. Previous reports have demonstrated the successful coupling of mesoporous TiO 2 additives to a C–S composite to improve the cycle life and the capacity retention. [ 6,17 ] It was shown recently that Li–S batteries could achieve 1000 cycles when the sulfur was coated with TiO 2 to create yolk–shell structures. [ 18 ] These results indicated that the mesoporous TiO 2 used in the coating layers promoted the interaction between TiO 2 and S, which was believed to be an electrostatic attraction (S–Ti–O) [ 6,19 ] that improved the surface adsorption of PS on the TiO 2 . Inspired by these results, and after comprehensively considering the three The development of advanced electrode materials with high energy/power density for energy storage is critical for a sustainable society. [ 1,2 ] Among existing materials, lithium–sulfur (Li–S) batteries show great potential for next-generation electrical energy storage applications. Sulfur cathodes, as well as being cost-effective and environmental friendly, provide a high theoretical capacity of 1675 mA h g −1 , a value that is an order of magnitude greater than typical values for conventional lithiated cathodes. [ 3 ] Despite the great promise of Li–S batteries, two main technical challenges must be addressed before they can fi nd practical use. First, the intrinsically poor electronic conductivity of sulfur leads to low use of the active material. Second, the high solubility of the polysulfi de’s (PS) reaction intermediaries (Li 2 S x , 4 < x < 8), and the action of their notorious “shuttle” mechanism in organic electrolytes, produce a rapid decline in the capacity, and a short cycle life. [ 4 ] To facilitate the development of the Li–S system, it is therefore crucial to improve the conductivity of the sulfur cathode and maintain/ reuse the soluble PS within the cathode structure. [ 5 ]

INVESTIGATION OF HOMOLOGOUS SERIES AS PRECURSORY HYDROCARBONS FOR ALIGNED CARBON NANOTUBE FORMATION BY THE SPRAY PYROLYSIS METHOD

The precursory carbon source is one of the key parameters which govern the formation of carbon nanotubes (CNTs). In this work, by selecting four homologous series, namely n-pentane, n-hexane, n-heptane and n-octane, as investigated targets, we comparatively study the relationship between thermodynamic properties of the precursory carbon source and formation of aligned CNTs. We find that all of these alkanes are favored for the growth of aligned CNTs in a suitable growth environment. But only n-heptane can yield the aligned CNTs with relatively high quality, high yield and narrow diameter distribution. Furthermore, after considering the link between thermodynamic properties of the precursory carbon source and the morphology characteristic of the nanotube samples, we find that the Gibbs free energy and formation enthalpy of precursory carbon sources play critical roles in the nanotube formation. In additions some possible explanations are proposed to better understand these phenomena. These rules will be ve...

Structure and growth of aligned carbon nanotube films by pyrolysis

Transmission electron microscopic study on the aligned carbon nanotubes has demonstrated a growth mechanism which involves two sizes of iron nanoparticles. While the small particle is catalytically active for the nucleation of the nanotube, the large particle produces the carbon atomistic species required for the growth of the nanotubes. The aligned nanotubes are believed to be the result of a competition growth process along the normal direction of the substrate. The surface diffusion of carbon atoms on the large iron particle leads to the formation of the observed bamboo-like structure. q 2000 Elsevier Science B.V. All rights reserved.

Sulfur–nitrogen co-doped three-dimensional carbon foams with hierarchical pore structures as efficient metal-free electrocatalysts for oxygen reduction reactions

Despite the good progress in developing doped carbon catalysts for oxygen-reduction reaction (ORR), the current metal-free carbon catalysts are still far from satisfactory for large-scale applications of fuel cell. Developing new metal free doped carbon materials with abundance active sites as well as excellent electron transfer and reactant transport rate towards ORR may be a potential solution. Herein, we develop a novel three-dimensional (3D) sulfur-nitrogen co-doped carbon foams (S-N-CF) with hierarchical pore structures, using a convenient, economical, and scalable method. The experimental results have demonstrated that the obtained 3D S-N-CF exhibited better catalytic activity, longer-term stability and higher methanol tolerance than a commercial Pt/C catalyst. Such excellent performances may be attributed to the synergistic effect, which includes high catalytic sites for ORR provided by high S-N heteroatom loading, excellent reactant transport caused by hierarchical pore structures and high electron transfer rate provided by 3D continuous networks. Our results not only develop a new type of catalysts with excellent electrocatalytic performance by a commercially valid route, but also provide useful information for further clarification of the relationship between the microstructures of metal-free carbon materials and catalyst properties for ORR. More importantly, the idea to design hierarchical pore structures could be applied to other catalytic materials and serve as a general strategy for improving the activity of various ORR catalysts.

From Hollow Olive-Shaped BiVO4 to n−p Core−Shell BiVO4@Bi2O3 Microspheres: Controlled Synthesis and Enhanced Visible-Light-Responsive Photocatalytic Properties

In this study, hollow olive-shaped BiVO(4) and n-p core-shell BiVO(4)@Bi(2)O(3) microspheres were synthesized by a novel sodium bis(2-ethylhexyl)sulfosuccinate (AOT)-assisted mixed solvothermal route and a thermal solution of NaOH etching process under hydrothermal conditions for the first time, respectively. The as-obtained products were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy, Brunauer-Emmett-Teller surface area, and UV-vis diffuse-reflectance spectroscopy in detail. The influence of AOT and solvent ratios on the final products was studied. On the basis of SEM observations and XRD analyses of the samples synthesized at different reaction stages, the formation mechanism of hollow olive-shaped BiVO(4) microspheres was proposed. The photocatalytic activities of hollow olive-shaped BiVO(4) and core-shell BiVO(4)@Bi(2)O(3) microspheres were evaluated on the degradation of rhodamine B under visible-light irradiation (λ > 400 nm). The results indicated that core-shell BiVO(4)@Bi(2)O(3) exhibited much higher photocatalytic activities than pure olive-shaped BiVO(4). The mechanism of enhanced photocatalytic activity of core-shell BiVO(4)@Bi(2)O(3) microspheres was discussed on the basis of the calculated energy band positions as well. The present study provides a new strategy to enhancing the photocatalytic activity of visible-light-responsive Bi-based photocatalysts by p-n heterojunction.

One-pot synthesis of N-doped carbon dots with tunable luminescence properties

N-Doped carbon dots synthesized by a one-pot solvothermal route displayed tunable luminescence due to different N contents. They could be directly applied in the imaging of peritoneal macrophages of mice. This study provides a new method to tune the luminescence of carbon-based materials through non-metal doping.

Metal-Catalyst-Free Growth of Single-Walled Carbon Nanotubes on Substrates

In this communication, we have demonstrated that SiO(2) nanoparticles can be generated by simply scratching the quartz or silicon wafer with a SiO(2) layer and confirmed it to be active for the growth of SWNTs for the first time. Furthermore, the SWNTs from SiO(2) has a much narrower size distribution. This may open a way to control the diameter of the SWNTs. More importantly, our work has found a series of oxides including Al(2)O(3), TiO(2), and rare earth oxides to be active for SWNT growth as well. These findings not only provide an alternative new type of catalysts for the growth of SWNTs but also give more insight into the role of the catalysts and a deeper understanding of the growth mechanism of SWNTs. The effective catalysts and catalytic activity for SWNT growth seem to be more size-dependent than the catalysts. Long oriented SWNTs generated from these catalysts enable us to rule out the relationship between the catalysts and the structures of the SWNTs. Thus controlled growth of SWNTs including the diameter and chirality is expected to be eventually realized.

Nonenzymatic electrochemical detection of glucose using well-distributed nickel nanoparticles on straight multi-walled carbon nanotubes

A nonenzymatic electrochemical sensor device was fabricated for glucose detection based on nickel nanoparticles (NiNPs)/straight multi-walled carbon nanotubes (SMWNTs) nanohybrids, which were synthesized through in situ precipitation procedure. SMWNTs can be easily dispersed in solution after mild sonication pretreatment, which facilitates the precursor of NiNPs binding to their surface and results in the homogeneous distribution of NiNPs on the surface of SMWNTs. The morphology and component of the nanohybrids were characterized by scanning electron microscopy (SEM) and X-ray powder diffraction (XRD), respectively. Cyclic voltammetry (CV) and amperometry were used to evaluate the catalytic activity of the NiNPs/SMWNTs nanohybrids modified electrode towards glucose. It was found that the nanohybrids modified electrode showed remarkably enhanced electrocatalytic activity towards the oxidation of glucose in alkaline solution compared to that of the bare glass carbon electrode (GCE), the NiNPs and the SMWNTs modified electrode, attributing to the synergistic effect of SMWNTs and Ni(2+)/Ni(3+) redox couple. Under the optimal detection conditions, the as-prepared sensors exhibited linear behavior in the concentration range from 1 μM to 1 mM for the quantification of glucose with a limit of detection of 500 nM (3σ). Moreover, the NiNPs/SMWNTs modified electrode was also relatively insensitive to commonly interfering species such as ascorbic acid (AA), uric acid (UA), dopamine (DA), galactose (GA), and xylose (XY). The robust selectivities, sensitivities, and stabilities determined experimentally indicated the great potential of NiNPs/SMWNTs nanohybrids for construction of a variety of electrochemical sensors.