Short-Range Nanoreaction Effect on the Hydrogen Desorption Behaviors of the MgH2-Ni@C Composite.

Doping a catalyst can efficiently improve the hydrogen reaction kinetics of MgH2. However, the hydrogen desorption behaviors are complicated in different MgH2-catalyst systems. Here, a carbon-encapsulated nickel (Ni@C) core-shell catalyst is synthesized to improve the hydrogen storage properties of MgH2. The complicated hydrogen desorption mechanism of the MgH2-Ni@C composite is elucidated. The experimental and theoretical calculation results indicate a short-range nanoreaction effect on the hydrogen desorption behaviors of the MgH2-Ni@C composite. The Ni@C catalysts and the adjacent MgH2 form nanoreaction sites along with preferential hydrogen desorption. The new interface between the in situ formed Mg and residual MgH2 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 MgH2-catalyst system.