Hydrogenation properties of mechanically milled Mg_2Ni_(0.8)Cr_(0.2)-CoO/Al_2O3 composites

摘要

Mg_2Ni_(0.8)Cr_(0.2)-x wt.% CoO/Al_2O_3 (x=0.5, 1, 2 and 3) composites were prepared by mechanically milling sintered Mg_2Ni_(0.8)Cr_(0.2) alloy and CoO/Al_2O_3 compound for 45 h. The addition of CoO/Al_2O_3 compound resulted in the good kinetics properties of hydriding/dehydriding reaction of the composites. The composite with 1.0 wt.% CoO/Al_2O_3 catalyst could reach the maximum hydrogen absorption capacity (2.9 wt.%) within 5 min at 393 K under H_2 pressure of 4 MPa, and can desorb rapidly at 493K. The decomposition and synthesis of hydrogen molecule on Mg_2Ni_(0.8)Cr_(0.2)alloy surface was promoted by addition of CoO/Al_2O_3 catalyst. In addition, the formation of metallic Ni particles, strain and defects during the ball milling process also resulted in the improved hydrogenation performance of Mg_2Ni-based alloys.