Study On Action Mechanism Of Metal In Hydrogen Storage Material

Mg/C hydrogen storage materials were prepared by reactive mechanical grinding, which is researched in this paper. Metal activators, pretreated anthracite and magnesium were grinded at hydrogen atmosphere. By transmission electron microscope (TEM), selected area electron diffraction (SAED), powder X-ray diffraction (XRD), differential scanning calorimeter (DSC) as well as self-devised drainage, the effects of metals on grindability, material size, hydrogen storage capacity and hydriding-dehydriding properties are emphatically researched. Fe,Co,Ni were added in pretreatment process of anthracite and the effects of the added metals are researched, also, the action mechanism of metals is discussed on the basis of experimental results.By the research of different content of Mg in ball grinding process, it is found that materials will have the conglutination effects, and the effects will be strengthened as the increase of Mg content; by the test of hydrogen storage capacity, it is indicated that the hydrogen storage densities presented increase firstly then decrease, and when Mg content is 60%, the capacity arrives the peak with the hydrogen storage capacity 4.78wt% of 60Mg40C and 7.37wt% of 60Mg(36C4Fe).Analysis of TEM shows that the average size of 50Mg40C10Al reaches 30⁵0nm after ball grinding at H₂ atmosphere for 2h; analysis of SAED indicates that hydrogen storage materials 50Mg40C10Al and 60Mg30C10Al both formed nano-crystalline and noncrystalline structure, but the size of 85Mgl5C without Al was obviously big; also, analysis of XRD displays that hydrogen storage material 50Mg40C10Al produced new substance MgH₂.By researching the catalysis action of metals in hydrogen storage materials, it is found that metal activators accelerate hydriding-dehydrding velocity of hydrogen storage materials in the process of grinding, and they also reduce the dehydriding temperature, enhance the hydrogen storage capacity of materials, and hasten the formation of similar-graphite microcrystal in the process of pretreatment.The catalysis action of metal activators to Mg-H₂ system is that they reduce the chemical enthalpy of forming hydride and make hydrogen molecules dissociate to hydrogen atoms easily, and they also provide new diffusion channels for hydrogen atoms, such as interface and defects diffusion, which accelerate solid phase diffusion velocity of hydrogen atoms. Another action is that they enhance brittleness of hydrogen storage materials and new surface is continuously formed in the process of hydriding-dehydriding cycle, and also the specific surface area of hydrogen storage materials is enlarged.