Chengxu Zhang

Engineering stepped edge surface structures of MoS2 sheet stacks to accelerate the hydrogen evolution reaction

Two-dimensional molybdenum sulfide is an attractive noble-metal-free electrocatalyst for the hydrogen evolution reaction (HER). Significant efforts have been made to increase the number of exposed edge sites. However, little attention has been paid to devising edge surface structures of MoS2 sheet stacks to promote the HER kinetics. Herein we report the first demonstration of significantly enhanced HER kinetics by controllably fabricating a stepped MoS2 surface structure. Vertical arrays of MoS2 sheets terminated with such a stepped surface structure have proved to be an outstanding HER electrocatalyst with an overpotential of 104 mV at 10 mA cm−2, an exchange current density of 0.2 mA cm−2 and high stability. Experimental and theoretical results indicate that the enhanced electrocatalytic activity of the vertical MoS2 arrays is associated with the unique vertically terminated, highly exposed, stepped surface structure with a nearly thermoneutral H-adsorption energy. This work opens a new avenue to designing and developing layered materials for electrochemical energy applications.

Hydrogen evolution electrocatalysis with binary-nonmetal transition metal compounds

The growing concern about global warming, environmental pollution and energy security has increased the demand for clean energy resources in place of fossil fuel. Cost-efficient generation of hydrogen from water splitting through electrocatalysis holds tremendous promise for clean energy. Central to electrocatalysis are efficient and robust electrocatalysts composed of earth-abundant elements, which are urgently needed for realizing low-cost and high-performance energy conversion devices. Transition metal compounds (TMCs) are a group of attractive noble-metal-free electrocatalysts for the hydrogen evolution reaction (HER). The incorporation of foreign nonmetal atoms into TMCs is a way of controllable disorder engineering and modification of their electronic structure, and thus may realize the synergistic modulations of both activity and conductivity for efficient HER performance. In the last few years, the interest in binary-nonmetal TMCs as an efficient HER electrocatalyst has grown exponentially owing to their fascinating electronic structure and chemical properties. Here, we sum up the recent developments of binary-nonmetal TMCs in HER electrocatalysis from the viewpoint of their tunable physicochemical properties. In addition, we identify major challenges ahead in this area and refine viable strategies and future research directions that will effectively address the said challenges.

Enhanced Pt performance with H2O plasma modified carbon nanofiber support

The insufficient durability and catalytic activity in low loading of platinum (Pt) are main obstacles to the development of low-temperature fuel cells. Our study demonstrated an efficient way to simultaneously improve the durability and electro-catalytic activity of Pt catalysts on carbon supports by water vapor (H2O) plasma functionalization. We report the finding that H2O plasma modification can introduce hydroxyl groups on carbon nanofiber (CNF) surface, and at the same time, highly preserve the microstructure of carbon support. Pt/CNF-H2O electrode possesses ultra-low Pt loading and superior electro-catalytic activity, poisoning-resistance ability and stability, suggesting a good candidate for fuel cell applications.

Local environment of Er3+ in Er-doped Si nanoclusters embedded in SiO2 films

The local environment of Er3+ in heavily Er-doped (Er, 2.5 at. %) Si nanoclusters embedded in SiO2 films annealed at various temperatures was investigated by using the fluorescence-extended x-ray absorption fine structure spectroscopy. The results show that annealing caused a large effect on the local environment of Er3+ surrounded by O atoms and the 1.54 mu m photoluminescence intensity. The correlation between the local environment around Er3+ and the corresponding 1.54 mu m photoluminescence was discussed. (c) 2006 American Institute of Physics.

Preparation of high-performance hydroxide exchange membrane by a novel ablation restriction plasma polymerization approach

A novel approach of ablation restriction plasma polymerization has been successfully demonstrated for the first time in hydroxide exchange membrane synthesis. The membrane possesses high hydroxide conductivity, alkaline stability, and the ability of fully encompassing catalyst particles, without solubility in low boiling point water-soluble solvents.

Magnetic properties of Ho2Co17-xGax compounds

We have studied the magnetic properties of Ho2Co17-xGax compounds (x less than or equal to 7) by means of magnetic measurements and X-ray diffraction on magnetically aligned powders. The Curie temperature and the spontaneous moment decrease strongly with increasing Ga concentration. The compounds that are magnetically ordered at roam temperature have an easy magnetisation direction at room temperature which is perpendicular to the c-direction

Structural and magnetic properties of R2(Fe,Si)17 compounds with R=Tb and Er

The structural and magnetic properties of R2F17-xSix compounds have been investigated by means of X-ray diffraction and magnetization measurements. Substitution of Si for Fe leads to a clear reduction of the unit-cell volume. With increasing Si content, a phase transition from the Th2Ni17- to the Th2Zn17-type of structure has been observed for R=Tb, while all compounds crystallize in the Th2Ni17-type of structure for R=Er. A clear decrease of the saturation moment and an increase of the Curie temperature have been found upon Si substitution. The exchange-interaction constant J(TbFe) between the Tb and the Fe moments has been obtained from a mean-field analysis of the Curie temperature T-c. The X-ray diffraction patterns of magnetically-aligned powder samples show that the easy magnetization direction is in the plane for all compounds investigated

Magnetic properties of YCo10Mo2−xMx compounds (M=Si or V)

Abstract YCo 10 Mo 2− x M x compounds (M=Si or V and x =0, 0.5, 1.0, 1.5, 2.0) with the ThMn 12 structure have been prepared by means of arc-melting and subsequent annealing. The magnetic properties have been investigated by X-ray diffraction on magnetically aligned powders, by a.c. susceptibility and by magnetization measurements. The lattice constants of the YCo 10 Mo 2− x M x compounds decrease linearly with increasing x , according to Vegards law. The magnetic properties of both series are different. Deviations of the spontaneous moment and the Curie temperature from a linear x dependence are observed, occurring in opposite directions in the two series investigated. This behaviour is discussed in terms of preferred Co-site occupation in the materials.

Plasma Discharge Process in a Pulsed Diaphragm Discharge System

As one of the most important steps in wastewater treatment, limited study on plasma discharge process is a key challenge in the development of plasma applications. In this study, we focus on the plasma discharge process of a pulsed diaphragm discharge system. According to the analysis, the pulsed diaphragm discharge proceeds in seven stages: (1) Joule heating and heat exchange stage; (2) nucleated site formation; (3) plasma generation (initiation of the breakdown stage); (4) avalanche growth and plasma expansion; (5) plasma contraction; (6) termination of the plasma discharge; and (7) heat exchange stage. From this analysis, a critical voltage criterion for breakdown is obtained. We anticipate this finding will provide guidance for a better application of plasma discharges, especially diaphragm plasma discharges.