Research On Preparation,Characterization And Electrochemical Properties Of Tungsten Oxide Hydrate And Tungsten Carbide

Tungsten-based nanomaterials have great potential in energy,chemical industry,alloy,catalysis and so on,which is due to their high melting point and structural stability.In recent years,low temperature combustion synthesis(LCS)is emerging as a new wet-chemical method for the preparation of nanopowders.This process is time-and energy-efficiency,simple and low-cost.In this paper,LCS methord was used to prepare tungsten-based nanomaterials.The main research work of the paper focus on several aspects as follows:(1)Nano-sized hexagonal WO3·0.33H2O/C is prepared by the solution combustion synthesis&hydrothermal method.This material has been used as the anode for high performance lithium-ion batteries for the first time.Carbon layer is uniformly coated on hexagonal WO3·0.33H2O nanoparticles.Prepared WO3·0.33H2O/C electrode shows high and reversible capacity of 768 mAh·g-1 after 200 cycles at 100 mA·g-1,which is higher than the reported orthorhombic WO3·0.33H2O/C.The specific structure can provide efficient channels for transporting Li+ swiftly.Therefore,hexagonal WO3·0.33H2O/C shows a great potential as the anode material for lithium-ion batteries.(2)Low temperature combustion route is developed for the synthesis of WO3·0.33H2O with different amounts of carbon as a composite anode for lithium ion batteries(LIBs).The electrochemical tests demonstrate that the lithium storage capacity of WO3·0.33H2O@C anode has been greatly improved by an appropriate amount of carbon coating,which could maintain a reversible discharge capacity of 816 mAh·g-1 after 200 cycles at 100 mA·g-1.Its long cycle stability and excellent rate capability are attributed to high electronic conductivity of the appropriate amorphous carbon layer and the unique hexagonal structure of the nanocomposite.(3)Tungsten carbide powder,which is used as the catalyst for a gas diffusion electrode,has been prepared by low-temperature combustion synthesis for the first time.The average particle size of the prepared tungsten carbide is 200 nm.The effects of the carbon/tungsten(C/W)molar ratio on the formation of tungsten carbide and carbon content on the complete carbonization temperature are discussed.The optimal synthesis temperature is 1100 ?,and the optimal C/W molar ratio is 19/3.Afer the oxygen reduction reaction test,the current density of the tungsten carbide-based gas diffusion electrode is as high as 350 mA·cm-2 at 0.4 V versus Hg/HgO.It is demonstrated that the tungsten carbide catalyst exhibits excellent electrocatalytic performance,comparable with that of Pt.(4)Different free carbon content of tungsten carbide can be obtained by changing the total carbonization temperature,and the content of free carbon in WC also increases gradually with temperature.The electrochemical properties of tungsten carbide prepared at different temperature for the oxygen reduction reaction are tested.The results show that the presence of the 0.98 wt%amorphous carbon is beneficial for improving the conductivity and dispersibility of tungsten carbide catalyst,and more active centers can be provided by the catalyst.(5)The Pt catalyst is reduced to the tungsten carbide surface by chemical reduction method.The prepared sample has a relatively fine and uniform size distribution.Since the amorphous carbon coating on the surface of prepared products,which plays a significant role in the microstructure of Pt/WC catalyst,improving the synergy of WC and Pt.The activity and mechanism for hydrogen evolution reaction(HER)are evaluated.While as compared with the WC catalyst and commercial Pt/C catalyst,Pt/WC catalyst shows the highest activity towards HER in acidic solution.This study indicates that the existence of free carbon could enhance the synergetic effect with the Pt/WC catalyst,leading to the increase of catalytic activity.(6)For the precious metal complex catalyst,the loading capacity and the fixed stability of Pt are still the main problems to be faced with.We demonstrate a strategy which can be used for mass-production for preparing a thickness-controllable double core-shell WC@C@Pt structure,based on a half combustion synthesis-carbonation method.By adjusting the carbon content of the precursors,the thickness of carbon layer covering the surface of tungsten carbide and the insertion depth of Pt particles into the carbon layer are controllable during the carbonation process.The carbon layer can fix the platinum particles as well as improve the electrical conductivity.This unique structure maintains a highly efficient and stable catalytic process,leading to its excellent performance for HER with low overpotentials and small Tafel slopes in acidic/alkaline solution.