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Abstract

Nanocrystalline Ti-catalyzed MgH₂ 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 MgH₂ sample. The catalyzed MgH₂ nanocrystalline sample consists of two MgH₂ phases—a tetrahedral β-MgH₂ phase and an orthorhombic high-pressure modification γ-MgH₂. Transmission electron microscopy was used for the observation of the morphology of the samples and to confirm the nanostructure. N₂ adsorption measurement shows a BET surface area of 108 m² g⁻¹ of the nanostructured material. This sample exhibits a hydrogen desorption temperature more than 130 °C lower compared to commercial MgH₂. After desorption, the catalyzed nanocrystalline sample absorbs hydrogen 40 times faster than commercial MgH₂ 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 MgH₂ nanocrystalline sample are 77.7 kJ mol⁻¹ H₂ and 138.3 J K⁻¹ mol⁻¹ H₂, respectively. Thermodynamic properties do not change with the nanostructure.