Effects of additive Pd on the structures and electrochemical hydrogen storage properties of Mg sub(67)Co sub(33)-based composites or alloys with BCC phase

Mg sub(67)Co sub(33) and Mg sub(67)Co sub(33)-Pd composites/alloys prepared by ball milling for 120 h possess nano-crystalline with body-centered cubic (BCC) structure, which was verified by high resolution transmission electron microscopy (HRTEM) and selected area electron diffraction (SAED) analyses. The introduced 5.0 at.% Pd significantly lifts the initial discharge capacity from 10 mAh g super(-1) of Mg sub(67)Co sub(33) to maximum 530 mAh g super(-1) Pd also drives the Mg sub(67)Co sub(33)-Pd composite forming a full BCC alloy during ball milling. The distribution of Pd gradually becomes homogeneous with the augmentation of the ball milling time according to the analyses by scanning electron microscopy-energy dispersive spectrometer (SEM-EDS). Exchange current density increased with the milling time and can be ascribed to the homogeneously dispersion of Pd over the surface. The introduced Pd also enhances the hydrogen diffusion coefficient of the Mg sub(67)Co sub(33)-Pd composites/alloys.