Effect of multi-wall carbon nanotubes supported nano-nickel and TiF₃ addition on hydrogen storage properties of magnesium hydride

Multi-wall carbon nanotubes supported nano-nickel (Ni/MWCNTs) with superior catalytic effects was introduced to magnesium hydride by the process of hydriding combustion synthesis (HCS) and mechanical milling (MM). The effect of different Ni/MWCNTs contents (5 wt.%, 10 wt.%, 15 wt.%, 20 wt.%) on the hydrogenation and dehydrogenation properties of the composite was investigated systematically. It is revealed that Mg₈₅-(Ni/MWCNTs)₁₅ composite shows the best comprehensive hydrogen storage properties, which absorbs 5.68 wt.% hydrogen within 100 s at 373 K and releases 4.31 wt.% hydrogen within 1800 s at 523 K under initial hydrogen pressures of 3.0 and 0.005 MPa, respectively. The in situ formed nano-Mg₂Ni and MWCNTs have excellent catalytic effect on the hydrogenation and dehydrogenation performances of MgH₂. To further improve the hydrogen absorption/desorption properties, TiF₃ was added to the Mg–Ni/MWCNTs system. The result shows that TiF₃ addition has little influence on the thermodynamic performance, but affects greatly the kinetic properties. The Mg₈₅-(Ni/MWCNTs)₁₅-TiF₃ composite exhibits an appreciably enhanced hydrogen desorption performance at low temperature, and the hydrogen desorption capacity within 1800 s at 473 K for the TiF₃-added composite is approximately four times the capacity of Mg₈₅-(Ni/MWCNTs)₁₅ under the same condition. The catalytic effects during hydrogenation and dehydrogenation have been discussed in the study. - Highlights: • The nanosized Ni/MWCNTs catalyst was successfully prepared. • Ni/MWCNTs shows superior catalytic effect on H absorption/desorption of Mg. • Mg₈₅-(Ni/MWCNTs)₁₅ composite shows the best hydrogen storage properties. • Ni/MWCNTs coupling with TiF₃ improves the hydriding/dehydriding properties largely.