Chen Qi-yuan

Synthesis and characterization of triclinic structural LiVPO4F as possible 4.2 V cathode materials for lithium ion batteries

AbstractA potential 4.2 V cathode material LiVPO4F for lithium batteries was prepared by two-step reaction method based on a carbon-thermal reduction (CTR) process. Firstly, V2O5, NH4H2PO4 and acetylene black are reacted under an Ar atmosphere to yield VPO4. The transition-metal reduction is facilitated by the CTR based on C→CO transition. These CTR conditions favor stabilization of the vanadium as V3+ as well as leaving residual carbon, which is useful in the subsequent electrode processing. Secondly, VPO4 reacts with LiF to yield LiVPO4F product. The property of the LiVPO4F was investigated by X-ray diffractometry (XRD), scanning electron microscopy (SEM) and electrochemical measurement. XRD studies show that LiVPO4F synthesized has triclinic structure(space group p % MathType!MTEF!2!1!+-% feaafiart1ev1aaatCvAUfKttLearuqr1ngBPrgarmWu51MyVXgatC% vAUfeBSjuyZL2yd9gzLbvyNv2CaeHbd9wDYLwzYbItLDharyavP1wz% ZbItLDhis9wBH5garqqtubsr4rNCHbGeaGqiVu0Je9sqqrpepC0xbb% L8F4rqqrFfpeea0xe9Lq-Jc9vqaqpepm0xbba9pwe9Q8fs0-yqaqpe% pae9pg0FirpepeKkFr0xfr-xfr-xb9adbaqaaeGaciGaaiaabeqaam% aaeaqbaaGcbaWaa0aaaeaacqaIXaqmaaaaaa!3BCC!

Determination of the standard enthalpy of formation of aqueous aluminum ion, Al3+(aq)

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A New Approach to the Electrochemical Decomposition of Aqueous Hydrogen Sulfide Solution into Sulfur and Hydrogen Gas

), isostructural with the naturally occurring mineral tavorite, LiFePO4·OH. SEM image exhibits that the particle size is about 2 μm together with homogenous distribution. Electrochemical test shows that the initial discharge capacity of LiVPO4F powder is 119 mA·h/g at the rate of 0.2C with an average discharge voltage of 4.2V (vs Li/Li+), and the capacity retains 89 mA·h/g after 30 cycles.

DSC studies on the kinetics of decomposition of manganese dioxide

Visible-light-responsive WO3 porous films were synthesized via step-voltage anodization in NH4F/(NH4)2SO4 solution and calcined at various temperatures.The crystalline phase and surface morphology were characterized using X-ray diffraction(XRD)and field emission scanning electron microscopy(FE-SEM).The as-anodized nanoporous films converted to a monoclinic phase with preferential orientation in the(020)planes,and the pore diameters of the films calcined below 450°C were estimated to be in the region of 50-100 nm.The photocatalytic activity was evaluated via photodegradation of methyl orange.The film calcined at 450°C showed the highest photocatalytic activity.Photoelectrochemical measurements showed that the incident photon-to-current conversion efficiency(IPCE)values of the film calcined at 450°C were 87.4%at 340 nm and 22.1%at 400 nm.Under visible light(λ≥400 nm),the photocurrent density in 0.5mo·lL-1 H2SO4 solution at 1.2V(vs Ag/AgCl(KCl saturated))was 5.11 mA·cm -2 . Electrochemical impedance spectroscopy(EIS)measurements showed that the film calcined at 450°C exhibited the smallest interface charge transfer resistance and optimal electroconductivity.Perfect crystallinity,high porosity and low resistance can therefore be obtained by controlling the calcination temperature.A large surface area and a porous structure are important factors in affecting photocatalytic activity.

Separation and Determination of Sulfur with Different Valance in Polysulfide Mixture

Abstract Heats of the reaction of aluminum with aqueous hydrochloric acid solution of different concentrations were calorimetrically measured. Combining with the thermodynamic properties of related substances, the standard enthalpy of formation of aqueous aluminum ion, Al 3+ (aq), was obtained as −538.25 ± 1.00 kJ · mol −1 .

Synthesis and Interfacial Electron Transfer of a Composite Film of Graphene and Tungsten Oxide

TiO2/Nb2O5 photocatalyst loaded with WO3 (WO3-TiO2/Nb2O5) was prepared by a modified hydrolysis process, and characterized by X-ray diffractometry, transmission electron microscopy, Raman spectra and UV-Vis diffuse refraction spectroscopy. The photocatalytic activity of WO3-TiO2/Nb2O5 was investigated by employing splitting of water for O2 evolution. The results indicate that WO3 loading can pronouncedly improve the photocatalytic activity of TiO2/Nb2O5 by using Fe3+ as an electron acceptor under UV irradiation. The optimum molar fraction of the loaded WO3 is 2%, and the largest speed of O2 evolution for 2% WO3-TiO2/Nb2O5 catalyst is 151.8 µmol/(L·h).

Effect of calcinationtemperature on the morphology and photoelectrochemical properties of anodizedWO3 nanoporous films

A new approach to the electrochemical decomposition of aqueous hydrogen sulfide solution into elemental sulfur and hydrogen gas has been proposed; this approach can be used to get rid of anode passivation caused by sulfur precipitated on the anode surface. After all sulfides, including S 2– , HS – and H2S in the anodic compartment, have been mostly converted into polysulfide ions, hydrogen sulfide gas is bubbled through the anolyte until the pH of the solution remains approximately constant. Sulfur is removed from the reaction mixture, which is then returned to the anode compartment where the unreacted sulfides and undecomposed lower polysulfide ions continue to undergo electrolysis into polysulfide ions, and then their decomposition by H2S gas again takes place. This cyclic process will lead to a high current efficiency with which aqueous H2S is electrochemically decomposed into sulfur and hydrogen gas without anode passivation. Results of both equilibrium calculations and experiments show the viability of this new approach.

Thermodynamic Analysis of Silicothermic Reduction Zinc Oxide in Vacuum

Abstract The kinetics of the thermal decomposition of manganese dioxide are studied with the DSC method. A non-isothermal reaction model consisting of two stages linked by the basic equation of interface reaction control is derived and the model agrees very well with the course of this decomposition reaction almost over the full range of reaction. Kinetic parameters for this reaction are calculated using this model and the methods of Kissinger, Duswalt and Ozawa.