Balancing Nanostructuring and Stability: How Ball-Milling Energy and Graphite Addition Control Hydrogen Storage and Air Resistance in MgH ₂

Solid-state hydrogen storage in magnesium hydride (MgH2) is limited by slow sorption kinetics, high desorption temperatures, and strong sensitivity to air exposure. Here, we systematically investigate how ball-milling energy, modulated through milling time, rotation speed, ball size, and graphite addition affect the microstructure, hydrogen storage performance, and oxidation resistance of MgH2-based materials. High-energy milling (300 rpm, 10 mm balls) promotes extensive crystallite refinement and large increases in surface area, not only resulting in the fast hydrogen uptake but also in strong susceptibility to air-driven degradation. Conversely, milder milling conditions (150 rpm, 3 mm balls) combined with 10 wt % graphite produced samples with a favorable balance between capacity (∼7 wt %), improved sorption kinetics, and markedly enhanced resistance to air exposure, with partial performance recovery after cycling even after one month in ambient atmosphere. The results reveal that optimizing ball-milling energy, not only through speed and time but also through ball mass, plays a critical role in achieving MgH2 materials that simultaneously exhibit high reactivity and environmental stability. These findings highlight a mechanochemical strategy for designing Mg-based hydrides with practical resistance to oxidation for hydrogen storage applications.