Three types of carbon fibers, PAN-based HSCF, pitch-based HMCF with low graphitization degree, and pitch-based CF70 with high graphitization degree, were used to prepare unidirectional carbon fiber rein-forced SiC composites (CF/SiC) by multiple impregnation of polycarbosilane and subsequent pyrolysis at 1200°C for 5-9 times. The experimental results showed that pyrolytic product of polycarbosilane at 1200°C in N₂ consisted of β-SiC phase in a nearly amorphous state and impurity oxygen. The impregnation behavior of polycarbosilane for CF70/SiC was different from those of HSCF/SiC and HMCF/SiC. CF70/SiC showed a flexural strength of 700MPa, which was markedly higher than those of HSCF/SiC and HMCF/SiC. Moreover, CF70/SiC exhibited non-catastrophic fracture behavior, whereas HSCF/SiC and HMCF/SiC showed brittle fracture behavior. Scanning electron microscope (SEM) and transmission electron microscope (TEM) observation of these composites clarified that HSCF/SiC and HMCF/SiC had a strong fiber/matrix interface bonding, whereas CF70/SiC had a weak interface bonding. It was concluded that highly graphitized CF70 was the most suitable reinforcement for the CF/SiC composite.

Guobin Zheng;Hideaki Sano;Yasuo Uchiyama;Kazuo Kobayashi;Kunio Suzuki;会明 成

Journal of the Ceramic Society of Japan

1998-12

A series of carbon based noble-metal-free catalysts for oxygen reduction reaction (ORR) has been designed and constructed, with the purpose of developing highly efficient but low-cost catalysts for fuel cell or metal-air battery applications. Their behaviors have been evaluated from both compositional and structural point of view. These new catalysts show very good ORR performance, which is comparable with commercial Pt/C in many aspects. The application of these advanced carbon materials has been further extended to energy storage (i.e. a lithium sulfur battery). According to our DFT calculation results, the soluble lithium polysulfides can be strongly anchored at a multiple nitrogen doping site and thus effectively suppress the undesirable shuttle effect. To achieve this, surface modification of graphene has been conducted by using graphitic carbon nitride. The abundant multiple nitrogen sites on carbon nitride has resulted in significantly improved battery performance, in both capacity and cycling stability.

Ji Liang;Lichang Yin;会明 成;Shizhang Qiao

2017

The carbon nanotubes possess many unique mechanical and electrical properties, and have been appreciated as new advanced materials for nanocomposite structures, particularly for the development of nanocomposite films. Nanotubes may also be used as nano-reinforcements for matrix system for fibre-reinforced plastic structures in order to improve out-of-plane properties, thus increasing the delamination resistance. However, those properties are highly relied on the structural integrity and homogeneity of the nanotube composites. Unfortunately, only a little works have paid much attention on these issues recently. It has been obviously proved that the atomic architecture on the nanotube's surface may be affected after the nanotubes were chemically reacted with polymer matrix. The weak bonding force among the different Jayers (bonded by a weak Van Der Waals attractive force) of multiwalled nanotubes may also cause a discontinuous stress transfer from the outershell to the inner of the composites. This paper reports the micro-hardness and flexural properties of nanotube composites with different amounts of nanotubes content. Experimental measurements and microscopic observations of the nanotube-epoxy composites before and after the tests are discussed in detail. The results show that the hardness of the nanotube composites varied with different nanotube weight fractions. The flexural strength decreased by 10% for a nanotube composite beam with 2wt.% of nanotubes. The SEM images also revealed that all nanotubes were completely pulled out after the flexural strength test due to a weak-bonding strength between the nanotube and matrix.

Kin Tak Lau;San Qiang Shi;Li Min Zhou;会明 成

Journal of Composite Materials

2003

Triangle defect states of hexagonal boron nitride (h -BN) atomic layer were studied by a density functional theory calculation. N(B) triangle defect states of h -BN atomic layer with N(B) edge atoms have acceptor (donor) levels. A cohesive energy calculation indicates that the h -BN atomic layer with N triangle defects is more or less stable, respectively, than that with B triangle defects when it is negatively or positively charged, which is consistent with the recent experimental observation of N triangle defects in h -BN atomic layer. Charge population analysis shows that the edge N(B) atoms surrounding the N(B) triangle defect are negatively (positively) charged. Such a charged triangle defects in h -BN may serve as a potential nanolens for electron-beam focusing.

Li Chang Yin;会明 成;Riichiro Saito

Physical Review B - Condensed Matter and Materials Physics

2010-4-15

会明 成;S. Akiyama;A. Kitahara;K. Kobayashi;B. L. Zhou

Scripta Materialia

1991-8

Multiwalled carbon nanotubes (MWNTs) functionalized with a water-soluble conducting polymer, sulfonated polyaniline (SPAN), were prepared by in situ polymerization of aniline followed by sulfonation with chlorosulfonic acid in an inert solvent and by hydrolysis in water. Electron microscopy, laser Raman spectroscopy, X-ray photoelectron spectroscopy, and UV-vis absorption spectroscopy were employed to characterize the morphology and chemical structure of the resulting product. The results show that the quinonoid structure of SPAN preferentially interacts with the nanotubes and is stabilized by strong π-π interaction between two components. The structure of MWNTs was not perturbed by the incorporation of SPAN, since the π-π interaction between MWNTs and SPAN is much weaker in comparison to that of the carbon covalent bond. The SPAN functionalized MWNTs are highly dispersible in water, thus opening new possibilities for their prospective technological applications.

Hui Zhang;Hong X. Li;会明 成

Journal of Physical Chemistry B

2006-5-11

An ultrasonic liquid infiltration technique has been developed for the fabrication of carbon fibre reinforced aluminium (CF/Al) precursor wires. The principal effect of ultrasound on aluminium infiltration into carbon fibres is considered to be caused by cavitation. The acoustic power required to produce cavitation in the present experimental system has been approximately calculated to be about 150 W, which is much greater than the requirement, several tens of watts, for overcoming the capillary pressure among carbon fibres. The observations on the morphology of the CF/Al precursor wires show that there are generally four states of infiltration: totally non-infiltrated, non-infiltrated in the centre and in some local regions of the wires, and completely infiltrated. It is found that carbon fibres can be sufficiently impregnated by molten aluminium given the appropriate application of ultrasound. Furthermore, a single fibre tensile test shows that there is no strength degradation of carbon fibres after aluminium infiltration. The CF/Al precursor wires obtained have an average fibre volume fraction of 26%. The maximum longitudinal tensile strength of the CF/Al wires is 605 MN m⁻², which implies a fibre strength transfer efficiency of 0·76.

会明 成;Z. H. Lin;B. L. Zhou;Z. G. Zhen;K. Kobayashi;Y. Uchiyama

Materials Science and Technology

1993-7

Large-scale implementation of electrochemical water splitting for hydrogen evolution requires cheap and efficient catalysts to replace expensive platinum. However, catalysts that work well at high current densities with ultrafast intrinsic activities is still the central challenge for hydrogen evolution. An ideal case is to use single atoms on monolayer two-dimensional (2D) materials, which simplifies the system and in turn benefits the mechanism study, but is a grand challenge to synthesize. Here, we report a universal cold hydrogen plasma reduction method for synthesizing different single atoms sitting on 2D monolayers. In the case of molybdenum disulfide, we design and identify a type of active site, i.e., unsaturated Mo single atoms on cogenetic monolayer molybdenum disulfide. The catalyst shows exceptional intrinsic activity with a Tafel slope of 36.4 mV dec^-1 in 0.5 M H₂SO₄ and superior performance at a high current density of 400 mA cm^-2 with an overpotential of ∼260 mV, based on single flake microcell measurements. Theoretical studies indicate that coordinately unsaturated Mo single atoms sitting on molybdenum disulfide increase the bond strength between adsorbed hydrogen atoms and the substrates through hybridization, leading to fast hydrogen adsorption/desorption kinetics and superior hydrogen evolution activity. This work shines fresh light on preparing highly efficient electrocatalysts for water splitting and other electrochemical processes, as well as provides a general method to synthesize single atoms on two-dimensional monolayers.

Yuting Luo;Shuqing Zhang;Haiyang Pan;Shujie Xiao;Zenglong Guo;Lei Tang;Usman Khan;Bao Fu Ding;Meng Li;Zhengyang Cai;Yue Zhao;Wei Lv;Qingliang Feng;Xiaolong Zou;Junhao Lin;会明 成;Bilu Liu

ACS Nano

2020-1-28

Modulating electronic structure of monolayer transition metal dichalcogenides (TMDCs) is important for many applications, and doping is an effective way toward this goal, yet is challenging to control. Here, the in situ substitutional doping of niobium (Nb) into TMDCs with tunable concentrations during chemical vapor deposition is reported. Taking monolayer WS₂ as an example, doping Nb into its lattice leads to bandgap changes in the range of 1.98–1.65 eV. Noteworthy, electrical transport measurements and density functional theory calculations show that the 4d electron orbitals of the Nb dopants contribute to the density of states of Nb-doped WS₂ around the Fermi level, resulting in an n- to p-type conversion. Nb-doping also reduces the energy barrier of hydrogen absorption in WS₂, leading to an improved electrocatalytic hydrogen evolution performance. These results highlight the effectiveness of controlled doping in modulating the electronic structure of TMDCs and their use in electronic related applications.

Lei Tang;Runzhang Xu;Junyang Tan;Yuting Luo;Jingyun Zou;Zongteng Zhang;Rongjie Zhang;Yue Zhao;Junhao Lin;Xiaolong Zou;Bilu Liu;会明 成

Advanced Functional Materials

2020

Integrating a semiconducting light absorber with an appropriate co-catalyst appears almost indispensable for photocatalytic solar fuel generation. Although ferroelectric materials with spontaneous electrical polarization are considered promising light absorbers with the ability to induce oppositely directed transport of photogenerated electrons and holes in the bulk, their applications are intrinsically restricted by the large Schottky barrier at the interface of the ferroelectric material and the co-catalyst, which has a larger work function. Here, we demonstrate that, by selective chemical epitaxial growth of anatase TiO₂ islands on the positively poled (00-1) facet of PbTiO₃ single-crystal particles to form an atomically smooth interface with a small potential difference, the material shows significantly improved photocatalytic hydrogen and oxygen generation under both UV-visible and visible light, while the island-free PbTiO₃ is inactive in visible light. This strategy may be applicable to various ferroelectric materials to produce unusual asymmetric micro-nano structures for excellent performance. Photocatalysis is intrinsically dependent on the synergy of three distinct steps, namely, light absorption, separation and transfer of photogenerated charge carriers, and surface catalysis. Ferroelectric materials such as tetragonal PbTiO₃ with a spontaneous polar field as light absorbers have unique directional transport of photogenerated electrons and holes in the bulk along the ferroelectric field so that the electrons and holes can reach different surfaces. Prior to inducing a catalytic reaction, the effective transfer of charge carriers from the ferroelectric photocatalyst to a suitable co-catalyst such as Pt is indispensable but usually limited by the large Schottky barrier between them. In this study, the selective epitaxial growth of anatase TiO₂ nano-islands on the positively poled (001¯) facet of PbTiO₃ is demonstrated to be effective in fully addressing such a limitation and greatly improving the photocatalytic activity of ferroelectric photocatalysts. Selective chemical epitaxial growth of anatase TiO₂ islands on the positively poled (001¯) facet of the ferroelectric PbTiO₃ photocatalyst can significantly boost photocatalytic hydrogen and oxygen generation under both UV-visible light and visible light largely as a result of the greatly lowered Schottky barrier between PbTiO₃ and co-catalyst Pt, promoting the charge transfer process between them. This strategy might be applied to modify various ferroelectric photocatalysts to produce unusual asymmetric micro-nano structures for excellent performance.

Gang Liu;Li Ma;Li Chang Yin;Gedeng Wan;Huaze Zhu;Chao Zhen;Yongqiang Yang;Yan Liang;Jun Tan;会明 成

Joule

2018-6-20