Zhoucheng Wang

Fabrication of ceramic composite coatings using electrophoretic deposition, reaction bonding and low temperature sintering

We have developed a novel combination of electrophoretic deposition (EPD), reaction bonding and low temperature sintering techniques for the fabrication of yttria stablised zirconia (YSZ)/alumina composite coatings on Fecralloys. A mixture of ethanol and acetylacetone solvent was found to be an effective medium for YSZ and aluminium particle suspension. With the particle size of YSZ and aluminium being significantly reduced during ball milling. By using the EPD process, uniform green form coatings containing YSZ and aluminium particles were produced on Fecralloys. After oxidation of aluminium at 500°C and sintering at 1200°C, a dense and adherent YSZ/Al2O3 coating was produced. The presence of aluminium in the green form coatings not only contribute to the bonding between the coating and the metal substrate, but also compensate for the volume shrinkage of the coatings during sintering by the volume expansion arising from oxidation of aluminium to alumina.

Vinyl ethylene sulfite as a new additive in propylene carbonate-based electrolyte for lithium ion batteries

Vinyl ethylene sulfite (VES) is studied as a new additive in propylene carbonate (PC)-based electrolyte for lithium ion batteries. The electrochemical results show that the artificial graphite material exhibits excellent electrochemical performance in a PC-based electrolyte with the addition of the proper amount of VES. According to our spectroscopic results, VES is reduced to ROSO2Li (R=C4H6), Li2SO3 and butadiene (C4H6) through an electrochemical process which precedes the decomposition of PC. Furthermore, some of the Li2SO3 could be further reduced to Li2S and Li2O. All of these products are proven to be components of the solid electrolyte interface (SEI) layer.

MOF-derived Co-doped nickel selenide/C electrocatalysts supported on Ni foam for overall water splitting

It is of prime importance to develop dual-functional electrocatalysts with good activity for overall water splitting, which remains a great challenge. Herein, we report the synthesis of a Co-doped nickel selenide (a mixture of NiSe2 and Ni3Se4)/C hybrid nanostructure supported on Ni foam using a metal–organic framework as the precursor. The resulting catalyst exhibits excellent catalytic activity toward the oxygen evolution reaction (OER), which only requires an overpotential of 275 mV to drive a current density of 30 mA cm−2. This overpotential is much lower than those reported for precious metal free OER catalysts. The hybrid is also capable of catalyzing the hydrogen evolution reaction (HER) efficiently. A current density of −10 mA cm−2 can be achieved at 90 mV. In addition, such a hybrid nanostructure can achieve 10 and 30 mA cm−2 at potentials of 1.6 and 1.71 V, respectively, along with good durability when functioning as both the cathode and the anode for overall water splitting in basic media.

Efficient Overall Water‐Splitting Electrocatalysis Using Lepidocrocite VOOH Hollow Nanospheres

Herein we report the control synthesis of lepidocrocite VOOH hollow nanospheres and further their applications in electrocatalytic water splitting for the first time. By tuning the surface area of the nanospheres, the optimal performance can be achieved with low overpotentials of 270 mV for the oxygen evolution reaction (OER) and 164 mV for the hydrogen evolution reaction (HER) at 10 mA cm-2 in 1 m KOH, respectively. Furthermore, when used as both the anode and cathode for overall water splitting, a low cell voltage of 1.62 V is required to reach the current density of 10 mA cm-2 , making the VOOH hollow nanospheres an efficient alternative to water splitting.

Fabrication of composite coatings using a combination of electrochemical methods and reaction bonding process

The major difficulty in fabricating ceramic coatings on metal substrates using the electrophoretic deposition process (EPD) is problems caused by the volume shrinkage during the sintering of the green form ceramic coatings produced by EPD. Numerous cracks normally form in the EPD coating during sintering. In this work, we have developed the reaction bonding process to fabricate crack-free and dense ceramic coatings, where the volume shrinkage is compensated by the volume expansion due to the oxidation of aluminium in the green form coatings during sintering in air. Both EPD and electroplating were used here to produce green form coatings which contain aluminium particles and, in some cases, an intermediate nickel layer. During the subsequent heat treatment, melting and oxidation of the metals in the green form coating promote densification during sintering. By these means, relatively dense composite coatings have been fabricated on metal substrates.

High performance Na-doped lithium zinc titanate as anode material for Li-ion batteries

A series of Li2−xNaxZnTi3O8 (x = 0, 0.05, 0.10, 0.15, 0.20) are prepared for the first time by a simple solid state method. Upon Na-doping, Rietveld refinement reveals that Na+ takes the 8c tetrahedral sites shared with Li+ and Zn2+ in the structure. Due to the larger ionic radius of Na+ than that of Li+, an increased disorder degree of ion locations in the structure is induced by Na doping. Furthermore, the lithium ion diffusion tunnel is also expanded after Na doping. Thus, higher lithium ion diffusion coefficient can be observed for all the Na-doped Li2ZnTi3O8 samples. However, phase analysis shows that high Na-doping content can result in the formation of impurity in the as-obtained titanates. Besides, the existence of too many Na ions in the spinel also decreases the structural stability. Therefore, Na-doping with low dose is beneficial to improve the electrochemical performance of Li2ZnTi3O8. Electrochemical evaluations show that Li1.95Na0.05ZnTi3O8 has the best lithium storage property among all the Li2−xNaxZnTi3O8. It can be found that Li1.95Na0.05ZnTi3O8 can deliver a reversible capacity of 267.3 mA h g−1 after 50 cycles. This finding can provide an experimental support to synthesize high performance Ti-based materials by Na doping.

Synthesis of 2D hollow hematite microplatelets with tuneable porosity and their comparative photocatalytic activities

α-Fe2O3 2D hollow microplatelets were synthesized by a facile one-pot template-free solvothermal method. The effect of synthetic parameters on the morphology and structure of the product was systematically studied. And the possible formation mechanism was proposed. Interestingly, by simply varying the concentration of NH4F, α-Fe2O3 hollow microstructures with similar platelet-like shapes but different porosities can be readily obtained. Their comparative photocatalytic activities were also investigated.

Facile synthesis of hematite nanostructures with controlled hollowness and porosity and their comparative photocatalytic activities

Hematite nanostructures with similar spindle-like shapes but different hollowness and porosities have been prepared by a facile hydrothermal method. The comparative photocatalytic activities of these samples were investigated and the results might be helpful to further understand the beneficial effects of hollow and porous structures.

Fluoroethylene Carbonate as an Electrolyte Additive for Improving the Performance of Mesocarbon Microbead Electrode

Conference Name:Symposium on Rechargeable Lithium and Lithium Ion Batteries Held During the 220th Meeting of the Electrochemical-Society (ECS). Conference Address: Boston, MA. Time:OCT 09-14, 2011.

CrN thin films prepared by reactive DC magnetron sputtering for symmetric supercapacitors

Supercapacitors have been becoming indispensable energy storage devices in micro-electromechanical systems and have been widely studied over the past few decades. Transition metal nitrides with excellent electrical conductivity and superior cycling stability are promising candidates as supercapacitor electrode materials. In this work, we report the fabrication of CrN thin films using reactive DC magnetron sputtering and further their applications for symmetric supercapacitors for the first time. The CrN thin film electrodes fabricated under the deposition pressure of 3.5 Pa show an areal specific capacitance of 12.8 mF cm−2 at 1.0 mA cm−2 and high cycling stability with 92.1% capacitance retention after 20 000 cycles in a 0.5 M H2SO4 electrolyte. Furthermore, our developed CrN//CrN symmetric supercapacitor can deliver a high energy density of 8.2 mW h cm−3 at the power density of 0.7 W cm−3 along with outstanding cycling stability. Thus, the CrN thin films have great potential for application in supercapacitors and other energy storage systems.