The ultrafine pure Mg and Mg-Ti particles were prepared through a direct current （DC） arc plasma method. The X-ray diffraction （XRD）, transmission electron microscopy （TEM）, pressure-composition-temperature （PCT） method and TG/DTA techniques were used to study the phase components, microstructure and hydrogen sorption properties of the powders before and after hydrogen absorption. It is revealed that most of the ultrafine Mg and Mg-Ti particles are hexagonal in shape with particle size in the range of 50-700 nm. According to the Van’t Hoff equation, the hydrogenation enthalpy of Mg-Ti powders is determined to be about -67 kJ/mol H2 based on the PCT curves of hydrogen absorption plateau pressures. This value is much higher than -78.6 kJ/mol H2 for pure Mg powders. TG/DTA analyses show that the onset dehydriding temperature of hydrogenated Mg-Ti powders is 386 °C, which is significantly lower than that of the hydrogenated Mg （423 °C）. The results prove that the addition of Ti into Mg through arc evaporation method can improve the thermodynamic properties of Mg for hydrogen storage.
