Study On The Synthesis Of Nanoscale RE-Al And The Catalytic Efficiency For The Hydrogen Storage Of NaAlH₄

NaAlH4 is the representative material of the light metal complex hydride for hydrogen storage. However, the high de/re hydrogenation temperature as well as the sluggish kinetics need to be improved. Based on the research of sodium alanate, NaAlH4 is scelected as the subject in this paper. Different methods to synthesis nanoscale RE-A1 have been found and the catalyst was added into the sodium alanate system to improve its hydrogen storage properties, The X-Ray Diffraction, the Sivert Hydrogen Storage Properties Tester, the Scanning Electron Micropy(SEM), the synchronized Differential Scanning Calorimetry-Thermogravimetry(DSC/TG) were employed to characterize the catalytic efficiency of RE-Al to the NaAlH4 system.Nanoscale CeAl4 could both be synthesized by the thermal reaction and ion exchange reaction. Comparing their yield, purity, particle size and uniformity, we chose the thermal reaction method as the preparation method of catalysts for the following studies. The nano CeAl4-doped sodium alanate (NaAlH4) was synthesized by ball milling NaH/Al with 0.04CeAl4 under hydrogen atmosphereat room temperature, and the catalytic efficiency of nanoscale CeAl4 for hydrogen storage of NaAlH4 was systematically investigated.It shows that CeAl4 can effectively improve the dehydrogenation properties of sodium alanate system. The 0.04CeAl4-doped NaAlH4 system starts to release hydrogen below 80 ℃, completes dehydrogenation within 10 min at 170 ℃, and exhibits good cycling de/hydrogenation kinetics at relatively lower temperature.Apparent activation energy of the dehydrogenation of NaAlH4can be effectively reduced by addition of CeAl4,resulting in the decrease of desorption temperatures. Moreover, by analyzing the reaction kinetics of nano CeAl-4-doped NaAlH4 sample, both of the dehydrogenation steps are controlled by the two-dimension phase-boundary growth theory. The mechanistic investigations gained here can help to understand the de-/rehydrogenation behaviors of catalyzed complex metal hydride systems.A series of nanoscale RE-Al(La,Pr,Nd,Sm) have been synthesized by the heat treatment reaction. The nano RE-A1 doped sodium alanate (NaAlH4) was synthesized by ball milling NaH/Al with 0.04 RE-A1 under hydrogen atmosphereat room temperature, and the catalytic performance of nanoscale RE-Al for the hydrogen storage properties of NaAlH4 was systematically investigatedand contrast the hydrogen storage properties of doping NaAlH4 system. The catalytic activity of the La3Al11-doped NaAlH4 is similar with the CeAl4-doped NaAlH4 and better than thePrAl3. NdAl3 and SmAl3-doped system. The hydrogen storage properties of PrAl3, NdAl3-doped NaAlH4 is similar with SmAl3-doped system in the first dehydrogenation step but present better properties in the second step. The reason of the phenomenon is the intermediate Na3AlH6 has been Lattice expansion, which could promote the dehydrogenation performance.