Synthesis, Characterization, and Hydrogen Storage Capacity of Magnesium Hydrides on Multi-walled Carbon Nanotubes
Multi-scale and/or multi-disciplinary approach to process-product innovation
Nanotechnology & Nanomanufacturing (T3-1)
Keywords: Magnesium hydride, Carbon nanotubes, Hydrogen storage, Nanocomposites
Magnesium hydride is one of the attractive and reversible hydrogen storage materials because it is directly formed from the reaction of bulk Mg with gaseous H2 and reaches a high theoretical H2 capacity of 7.6 wt.%. Such a storage system can store H2 safely at an energy density equivalent to almost 100 g/L. In addition, MgH2 is also an abundant, low cost, easy to handle, and environmentally kindly light-metal hydrides. However, the practical application of Mg as a H2 storage medium is greatly hindered by its high desorption temperature and slow absorption/desorption kinetics. Therefore, the microstructure and absorption/desorption characteristics of composite MgH2 and 2-6 wt.% as-prepared multi-walled carbon nanotubes (MWCNTs) were investigated. The synthetic mechanisms, fine structures, surface properties of MgH2/MWCNTs were also identified by EDS, XRPD, X-ray absorption near edge structure (XANES)/extended X-ray absorption fine structure (EXAFS) and TGA techniques. The MWCNTs were produced from the catalytic-assembly benzene-thermal routes by reduction of C6Cl6 with metallic K or Na in the presence of Co/Ni catalyst precursors at 503-623 K. MgH2/MWCNTs were obtained by a mechanically well-mixing or grinding route. The H2 storage capacity of MgH2 and MgH2/MWCNTs were conducted and measured by a TGA microbalance method. The experimental data indicate that the MgH2/MWCNTs samples exhibits faster absorption kinetics and relatively lower desorption temperature than pure MgH2 or MgH2/MWCNTs (purified) nanocomposites. Hydrogen storage capacities of 6.0, 4.2, and 3.5 wt.% for MgH2/MWCNTs were achieved in 1h at 423, 373, and 298 K, respectively. In addition, the different effects of MWCNTs and metallic nanocatalysts contained in the MWCNTs were studied and a hydrogenation mechanism was also postulated. It is suggested that the metallic nanoparticles may be mainly responsible for the improvement of the H2 absorption kinetics, and MWCNTs for the enhancement of H2 absorption capacity of light MgH2.
Presented Monday 17, 16:20 to 16:40, in session Nanotechnology & Nanomanufacturing (T3-1).
