Short-Range Nanoreaction Effect on the Hydrogen Desorption Behaviors of the MgH 2 -Ni@C Composite.

Doping a catalyst can efficiently improve the hydrogen reaction kinetics of MgH. However, the hydrogen desorption behaviors are complicated in different MgH-catalyst systems. Here, a carbon-encapsulated nickel (Ni@C) core-shell catalyst is synthesized to improve the hydrogen storage properties of MgH. The complicated hydrogen desorption mechanism of the MgH-Ni@C composite is elucidated. The experimental and theoretical calculation results indicate a short-range nanoreaction effect on the hydrogen desorption behaviors of the MgH-Ni@C composite. The Ni@C catalysts and the adjacent MgH form nanoreaction sites along with preferential hydrogen desorption. The new interface between the in situ formed Mg and residual MgH contributes to the subsequent hydrogen desorption. With the nanoreaction sites increased via adding more catalyst, the short-range nanoreaction effect is more prominent; as a comparison, the interface effect becomes weaker or even disappears. In addition, the core-shell structure catalyst shows ultrahigh structural stability and catalytic activity, even after 50 hydrogen absorption and desorption cycles. Hence, this study provides new insights into the complicated hydrogen desorption behaviors and comes up with the short-range nanoreaction effect in the MgH-catalyst system.