| Tungsten carbide has been used as an alternative electrocatalyst due to its catalytic behavior is similar to that of platinum catalyst,its higher tolerance to CO?H2S poisoning,but its catalytic activity is much lower than that of platinum group noble metal.How to improve its catalytic activity is one of the difficult points and hot topics in recent years.Montmorillonite(MMT)is natural layered silicate with several excellent properties,such as electronegativity surface,huge specific surface area,strong adsorbability,and cation-exchage ability et al.Under the inspiration of these properties of nanoscale MMT piece,MMT nanolayer was obtained by exfoliated and used as a suitable support to tungsten carbide,WC/MMT nanocomposite was successfully prepared,in which WC nanopartiles with high specific surface area and small nanoscale loads on the surface of MMT nanolayer.And its electrocatalytic activity was tested by CHI620 elecrochemical work station mainly.Based on the above works,the following results and conclusions can be drawn:(1)Montmorillonite was exfoliated by an intercalated approach,using lithium chloride(LiCl),n-butyl lithium(n-BuLi)and glucose acid(GA)as reactants.The results show that after exfoliated by LiCl,the layer structure of montmorillonite preserves,the dispersion of the sample is well,and the diffraction peak of(001)plane left shifts 1.2°,corresponding to the increasing of the interplane distance of(001)plane for 0.27 nm,and some particles are of single layer,with a thickness of 5?10 nm and edge rolled;after exfoliated by n-BuLi,the diffraction peak of(001)plane of the sample disappears.This indicates that the layer structure of montmorillonite destroyed after exfoliated,and some nano-pieces with a thickness of 10?15 nm displays;after exfoliated by glucose acid,the disorder of montmorillonite structure is increased,and the particle stacked up obviously.Comparing these three exfoliated methods,it is obviously that the efficiency of montmorillonite structure exfoliated by LiCl and n-BuLi is better than that by glucose acid.(2)WC/MMT nanocoraposites were prepared through combination an impegnation approach with a reduction-carbonization method,using MMT exfoliated by LiCl as support.The formation mechanism and the effect of the preparing parameters on the microstructure of the composite were investigated,and the results show that when the molar ratio of tungsten to MMT is 2?4,carburizing time is 5h,and the temperature is 1073K,the crystal phase of the sample is composed of WC and WZC,with a diameter about 12nm,and WC particles disperse on the surface of MMT nanolayer.(3)The electrocatalytic activity for methanol electro-oxidation of the nanocomposite was measured by a micro-powder electrode.The results imply that WC/MMT is electrocatalytic active for methanol oxidation in acidic and alkaline solution,and the electrocatalytic property of the sample in alkaline solution is better than that in acidic solution.When the molar ratio of tungsten/MMT is 2?4,carburizing time is 5h,the electro-oxidation property of the sample is strongest,and there is a synergistic effect between tungsten carbide and montmorillonite.(4)The electrocatalytic activity for p-nitrophenol electro-reduction of the nanocomposite was measured by glassy carbon electrode.The results imply that electro-reduction property in acidic solution is stronger than that in neutral and alkaline solution.The process of the electrocatalytic reduction of WCfMMT for PNP is controlled by adsorption diffusion process and this process is chemical stability.When the crystal phase of the sample is composed of WC+W2C,its electrocatalytic property for PNP is the best,which implies that WC+W2C are more active than pure WC for PNP electroredution.Based on the above results,one conclusion can be drawn that tungsten carbide decorating on the outside surface of MMT is one of the efficacious ways to improve its electrocatalytic activity. |
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