Investigation on Gaseous and Electrochemical Hydrogen Storage Kinetics of As-Quenched Nanocrystalline Mg2Ni-type Alloys

In order to improve the gaseous and electrochemical hydrogen storage kinetics of the Mg2Ni-type alloys, Ni in the alloy was partially substituted by element Cu. Rapid quenching technology was used for the preparation of the Mg2Ni1-xCux (x = 0, 0.1, 0.2, 0.3, 0.4) hydrogen storage alloys. The structures of the as-cast and quenched alloys were characterized by XRD, SEM and TEM. The gaseous hydrogen absorption and desorption kinetics of the alloys were measured by an automatically controlled Sieverts apparatus. The electrochemical hydrogen storage kinetics of the as-quenched alloys was tested by an automatic galvanostatic system. The results show that all the as-quenched alloys hold an entire nanocrystalline structure and are free of amorphous phase. The substitution of Cu, instead of changing the major phase Mg2Ni, leads to a visible refinement of the grains of the as-cast alloys. Furthermore, both the rapid quenching treatment and Cu substitution significantly improve the gaseous and electrochemical hydrogen storage kinetics of the alloys. As the quenching rate grows from 0 (as-cast is defined as quenching rate of 0 m/s) to 30 m/s, the hydrogen absorption saturation ratio in 5 min, for the Mg2Ni0.7Cu0.3 alloy, increases from 57.2% to 92.8%, the hydrogen desorption ratio in 20 min from 21.6% to 49.6%, the high rate discharge ability (HRD) from 40.6% to 73.1%, the hydrogen diffusion coefficient (D) from 1.02×10−11 to 4.08×10−11 cm2/s and the limiting current density (IL) from 113.0 to 715.3 mA/g.