Activation and hydrogen storage properties of Mg-based composites synthesized by catalytic mechanochemical hydrogenation strategy

To ameliorate the activation performance and absorption/desorption properties, Mg-based composites are prepared via catalytic mechanochemical hydrogenation (CMCH) strategy by TiF3 or Nb2O5 or both. The results show that multiple H2 filling mechanochemical hydrogenation (MCH) way is in favour of the transformation from Mg to MgH2. The hydrogenation process and hydrogenation degree of Mg can be effectively accelerated via CMCH with TiF3 or Nb2O5 or both. The complete hydrogenation time for CMCH Mg–TiF3 and Mg–TiF3–Nb2O5 is compressed to 12 h, which is much shorter than those of CMCH Mg–Nb2O5 and Mg systems. The hydrogenation capacities at 3rd activation cycle of 12 h CMCH Mg–TiF3, Mg–Nb2O5 and Mg–TiF3–Nb2O5 are 5.87, 5.74 and 5.38 wt%, which corresponding to 81.3%, 79.5% and 74.5% activation rates. The hydrogenation capacities at 3rd activation cycle of 20 h CMCH Mg–TiF3, Mg–Nb2O5 and Mg–TiF3–Nb2O5 are 6.56, 7.08 and 7.18 wt% with 90.9%, 98.1% and 99.4% activation rates. The absorption capacities of CMCH Mg–TiF3, Mg–Nb2O5 and Mg–TiF3–Nb2O5 at 350 °C under 3 MPa pressure within 0.5 h are 5.75, 5.74 and 4.67 wt%. The dehydrogenation peak temperatures of γ-MgH2 reduce to 367.37 °C and 366.59 °C and the initial desorption temperatures are 355.77 °C and 351.39 °C of 12 h and 20 h CMCH Mg–TiF3–Nb2O5 at 5 °C/min heating rate. The lowest dehydrogenation peak temperatures of 391.73 °C and 389.81 °C are achieved by 12 h and 20 h CMCH Mg–TiF3–Nb2O5 samples. The catalytic mechanochemical hydrogenation has been proved to be a feasible and effective strategy for fast acquisition of Mg-based hydride composites with expected hydrogen storage performance.