Nanostructured Ti-catalyzed MgH_2 for hydrogen storage

摘要

Nanocrystalline Ti-catalyzed MgH_2 can be prepared by a homogeneously catalyzed synthesis method. Comprehensive characterization of this sample and measurements of hydrogen storage properties are discussed and compared to a commercial MgH_2 sample. The catalyzed MgH_2 nanocrystalline sample consists of two MgH_2 phases-a tetrahedral β-MgH_2 phase and an orthorhombic high-pressure modification γ-MgH_2. Transmission electron microscopy was used for the observation of the morphology of the samples and to confirm the nanostructure. N_2 adsorption measurement shows a BET surface area of 108m ~2g~(-1) of the nanostructured material. This sample exhibits a hydrogen desorption temperature more than 130 °C lower compared to commercial MgH_2. After desorption, the catalyzed nanocrystalline sample absorbs hydrogen 40 times faster than commercial MgH_2 at 300 °C. Both the Ti catalyst and the nanocrystalline structure with correspondingly high surface area are thought to play important roles in the improvement of hydrogen storage properties. The desorption enthalpy and entropy values of the catalyzed MgH_2 nanocrystalline sample are 77.7kJmol~(-1)H_2 and 138.3JK~(-1)mol ~(-1)H_2, respectively. Thermodynamic properties do not change with the nanostructure.