Kinetics of hydrogen absorption and desorption of a mechanically milled MgH_2+ 5at percent V nanocomposite

摘要

The experimental data in the MgH_2-5at percent V composite was summarized and used to investigate the kinetic mechanism of hydrogen absorption and desorption using a new model. The research results indicate that a coincidence of the theoretical calculation values with the experimental data has been reached and the rate-limiting step is hydrogen diffusion through the hydride phase (beta phase) with the activation energy of 47.2 kJ per mole H_2 for absorption and the diffusion of hydrogen in the a solid solution (a phase) with that of 59.1 kJ per mole H_2 for desorption. In addition, the hydriding rate of the MgH_2-V composite is 2.9 times faster than that of MgH_2 powders when compared with their characteristic absorption time directly.