Remarkable hydrogen storage properties at low temperature of Mg-Ni composites prepared by hydriding combustion synthesis and mechanical milling

Mg_100-xNi_x (x = 0, 5, 10 and 20) composites with the main particle size below 400 nm were synthesized by hydriding combustion synthesis followed by mechanical milling (HCS + MM). XRD and TEM results of Mg_100-xNi_x revealed that the products had the phases of MgH₂, Mg₂NiH₄, Mg₂NiH_0.3 and Mg (Mg just for x = 0 and 5), with Mg-Ni hydrides distributing uniformly in the composites. DSC results of Mg_100-xNi_x composites demonstrated that the hydrogen desorption peak for MgH₂ in the Mg₈₀Ni₂₀ composite was decreased to 223.9/247.3°C. With 5 at% Ni added, the Mg₉₅Ni₅ reached its saturated hydrogen absorption capacity of 5.80 wt% within 100 s at 473 K. As for Mg₈₀Ni₂₀, a hydrogen absorption of 3.70 wt% at 313 K and a desorption capacity of 1.84 wt% at 473 K could be obtained. The Mg₂Ni distributing uniformly in Mg-Ni composites significantly facilitates hydrogen diffusion and improves the hydriding/dehydriding kinetics and hydrogen storage capacity at low temperature. The amount of Ni is related greatly to the hydriding/dehydriding properties of Mg_100-xNi_x, which makes the hydrogen storage capacity and hydriding/dehydriding kinetics remarkable. Besides, the excellent cycling stability was also obtained through the isothermal de/hydrogenation cycling kinetics measurement.