Hydrogen Storage Properties of Graphite-Modified Mg-Ni-Ce Composites Prepared by Mechanical Milling Followed by Microwave Sintering

The Mg₁₇Ni_1.5Ce_0.5 hydrogen storage composites with different contents of graphite were prepared by a new method of mechanical milling and subsequent microwave sintering. The small particle size (~25 ??m) and the low echo ratio of power indicate that graphite plays an important role not only as a lubricant during mechanical milling but also as a supplementary heating material during microwave sintering. As a catalyst in the hydriding/dehydriding (H/D) reaction, graphite also improved the hydrogen storage properties of the composites. The hydrogen absorption and desorption capacities of Mg₁₇Ni_1.5Ce_0.5 with 5 wt pct graphite were 5.34 and 5.30 wt pct H₂ at 573 K (300 °C), its onset temperature of dehydriding reaction was 511 K (238 °C), and its activation energies of H/D reaction were 40.9 and 54.5 kJ/mol H₂, respectively. The kinetic mechanisms of the H/D reaction are also discussed.