Controllable Preparation And Performance Study Of Transition Metal Compounds Nanomaterials

In recent years, transition metal compounds nanomaterials have been widely used in catalysis, sensor, photoelectric conversion, data storage,coating and abrasive materials due to their rich and excellent physical and chemical properties. Expecially for two typical photo- or electro-chemistry reactions in the fields of environment and energy: photocatalytic degradation and oxygen reduction reaction (ORR) electrocatalysis, the representative transition metal oxides, carbides, nitrides and oxynitrides nanomaterials photo- or electro-catalysts also show certain catalytic activity, high stability and excellent ability of resistance to poisoning. At the same time, novel multifunctional nanocomposites developed by introducing one or more nanostructures into another nanomaterials uaually exhibit enhanced or new physical and chemical properties owing to the synergistic effect between different componements. Herein, we carry out the research of supporters or co-catalysts loaded transition metal compounds composites catalysts successfully in order to achieve enhanced photo-degradation or ORR electro-catalytic performance, the main content includes the following three aspects:(1) Synthesis and catalytic performance of reduced graphene oxide(RGO) supported transition metal oxides nanostructures (ZnO nanorods,CeO2 nanocubes, ZnGa2O4 nanoparticles and Li3VO4/LiV3O8 nanobelts)composites. Experiments results show that such composits materials can be effective prepared due to the interaction between the surface oxygen-containing groups on graphene oxide (GO) sheets and transition metal ions or oxides as well as the further reduction of GO sheets. Moreover, the introduction of RGO sheets in composits can also enhance photo-degradation or ORR catalytic performance. For example, ZnO nanorods composites exhibit a 6.8 times enhanced photocatalytic activity of the degration of RhB dyes, CeO2 nanocubes composites also show a 30%higher photocatalytic acticity towards the degration of MB dyes, and the phtocatalytic activities of ZnGa2O4 nanoparticles composities for the the degration of RhB and MB dyes advance 2.2 times and 2.5 times respectively, comparing with pure metal oxides nanostructures catalysts.The onset potential values, current densities, Tafel slopes, number of transferred electrons and electrochemical stabilities for Li3VO4/LiV3O8 nanobelts based composites during ORR also improve to a certain degree.(2) Synthesis and electrocatalytic performance of graphite carbon supported transition metal (V, Nb, W and Mo) carbides and nitrides nanoparticles composites. The measurements prove that vanadium nitride nanoparticles based composite material with a morphology similar to the graphene-metal oxides nanoparticles composites exhibits the most excellent oxygen reduction catalytic activity (the diffusion-limited current density of VN/C electrode is 4.12 mA cm-2 at 1600 rpm, almost 80 percent of that of Pt/C electrode), stability and ability to resist methanol poisoning.(3) Synthesis and electrocatalytic performance of carbon nanotubes(CNTs) supported porous vanadium oxynitride nanoribbons (VOxNy NRs)composites. The electrochemical tests results show that this composite material as a suitable non-noble metal oxygen reduction electrocatalyst candidate has excellent oxygen reduction catalytic activity (the diffusion-limited current density is about 0.4 mA cm-2 larger), stability and ability to resist methanol poisoning, can be further used as a suitable non-noble metal oxygen reduction electrocatalyst candidate.To summarize, the relative innovations in this context chiefly cover the developmet of new preparation methods and technology and the elaboration of catalytic performance enhancement mechanism. First, this text presents a green single or two step hydrothermal (solvothermal)process as well as intercalation assembly method to prepare nanocomposites of reduced graphene oxide (RGO) supported transition metal oxides. And RGO sheets in the composites can inhibit the recombination of photo-generated electron and hole pairs on the surface of transition metal oxides nanostructures and increase the transfer of charge as well as the diffusion of related process materials, so as to advance the photo- or electro- catalytic performance. Then, a single step temperature-programmed heating method under inert atmosphere to prepare graphite carbon supported transition metal carbides or nitrides nanoparticles composites is further developed. The unique structural features of surface metal oxides and capped carbon layers can lead to a certain catalytic activity, superior stability and methanol tolerance. A typical topotactic reaction during the temperature-programmed process under ammonia condition is finally put forward to synthesize VOxNy-CNTs composites.The porous structure contributes to the well contact among the electrolyte,the surface of electrocatalyst and oxygen, and the introduction of carbon nanotubes with surface carbon-nitrogen bonds can further improve the electrical conductivity and decrease the overpotential of ORR process.