A review of enhanced hydrogen storage in MgH2: the role of high-energy reactive ball milling and catalysis

Due to its significant hydrogen capacity (7.6 wt%), availability, and reversibility, magnesium hydride (MgH2) is considered one of the most promising solid-state hydrogen storage materials, making it attractive for sustainable energy systems. The excellent thermodynamic stability and slow absorption/desorption kinetics, which require elevated operating temperatures, limit its practical application. This paper addresses the important issue of how advanced synthesis methods, specifically high-energy reactive ball milling and catalytic doping, can overcome inherent challenges and enable the practical use of MgH2 for hydrogen storage. The methodology adopted is a systematic and integrative review of state-of-the-art experimental and theoretical studies, focusing on thermodynamic and kinetic fundamentals, synthesis routes, catalytic additives, and nanostructuring strategies. Results indicate that high-energy ball milling significantly improves hydrogen diffusion by reducing particle sizes to the nanoscale and lowering the desorption onset temperature by approximately 45 °C. Catalysts such as 2 mol% Nb2O5 further reduce activation energy barriers, enabling rapid hydrogen release of 6.4 wt% in 114 s, while polymorphic transitions (γ-MgH2 formation) enhance structural stability. Despite these advances, challenges such as grain coarsening and cycling capacity loss remain, highlighting the importance of nanoencapsulation, alloying, and scalable fabrication techniques. In conclusion, the review provides a critical framework for understanding the synergistic role of ball milling and catalysis in tailoring MgH2 properties and outlines future research directions toward efficient, scalable, and application-ready hydrogen storage systems.