Mg(AlH 4 ) 2 nanoparticles with a particle size less than 10 nm have been successfully synthesized by mechanochemical method using LiAlH 4 and MgCl 2 as raw materials together with LiCl buffering additive. In comparison to Mg(AlH 4 ) 2 microparticles, Mg(AlH 4 ) 2 nanoparticles exhibit a faster hydrogen desorption kinetics and lower desorption temperature. The hydrogen desorption temperatures of the first and second dehydrogenation steps are 80 and 220 °C for the Mg(AlH 4 ) 2 nanoparticles, which are about 65 and 60 °C, respectively, lower than those of Mg(AlH 4 ) 2 microparticles. The decomposition activation energy is reduced from 135 kJ/mol for Mg(AlH 4 ) 2 microparticles to 105.3 kJ/mol for Mg(AlH 4 ) 2 nanoparticles. It is proposed that the shortened diffusion distance and enhanced diffusivity of Mg(AlH 4 ) 2 /MgH 2 nanoparticles provide an energy destabilization for lowering the dehydrogenation temperature, and thus being the key factor for promoting the hydrogen desorption kinetics. More importantly, it is demonstrated that the dehydrided nano MgH 2 hydride with a particle size below 10 nm can be formed after rehydrogenation process, resulting in the good cycling hydrogen desorption performance of nano MgH 2 .
Yuepeng Pang,Yongfeng Liu,Xin Zhang,Qian Li,Mingxia Gao,Hongge Pan
Herein, an initial attempt to understand the relationships between hydrogen storage properties, reaction pathways, and material compositions in LiBH 4 – x Mg(AlH 4 ) 2 composites is demonstrated. The hydrogen storage properties and the reaction pathways for hydrogen release from LiBH 4 – x Mg(AlH 4 ) 2 composites with x =1/6, 1/4, and 1/2 were systematically investigated. All of the composites exhibit a four-step dehydrogenation event upon heating, but the pathways for hydrogen desorption/absorption are varied with decreasing LiBH 4 /Mg(AlH 4 ) 2 molar ratios. Thermodynamic and kinetic investigations reveal that different x values lead to different enthalpy changes for the third and fourth dehydrogenation steps and varied apparent activation energies for the first, second, and third dehydrogenation steps. Thermodynamic and kinetic destabilization caused by the presence of Mg(AlH 4 ) 2 is likely to be responsible for the different hydrogen desorption/absorption performances of the LiBH 4 – x Mg(AlH 4 ) 2 composites.
危险品化学品经营许可证（带存储）