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.%.