Significantly enhanced hydrogen desorption properties of Mg(AlH4)2 nanoparticles synthesized using solvent free strategy

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 .