Influence of Pd on the structure and electrochemical hydrogen storage properties of Mg50Ti50 alloy prepared by ball milling

High-energy ball milling was used to modify the physico-chemical and the electrochemical hydrogenation properties of Mg50Ti50 alloy via the addition of Pd. This was done by first ball milling Mg and Ti together for (20 − x) hours. 3.3 at.% Pd was then added and ball milling was resumed for x hours. X-ray diffraction and X-ray photoelectron spectroscopy analyses revealed that the alloying of Pd with pre-milled Mg50Ti50 was initiated after only a few minutes and was completed after 5 h of milling. The maximum discharge capacity of the Mg50Ti50–3.3 at.% Pd electrode increased significantly with the milling time (from 35 mAh g−1 for 5 min to 480 mAh g−1 for 20 h of milling). The exchange current density increased with the milling time and was directly related to the Pd surface concentration, suggesting that Pd plays a key role in facilitating the charge-transfer reaction. In contrast, the incorporation of Pd had a minor effect on the hydrogen diffusion coefficient. The electrochemical pressure-composition isotherms revealed a significant destabilization of the hydride as the milling time with Pd increased. No significant improvement in the hydrogen storage properties of Mg50Ti50–Pd electrodes was observed for Pd concentrations higher than 3.3 at.%.