Magnesium hydride (MgH2) has emerged as a promising candidate for reversible hydrogen storage due to its high theoretical hydrogen capacity of 7.6 wt%, abundance, and relatively low cost. However, its practical application has been hindered by slow kinetics, high desorption temperatures, and poor cycle life. Recent advances in catalyst doping, nanostructuring, and mechanical processing have addressed some of these challenges, making MgH2 composites a viable option for stationary hydrogen storage systems.

One of the most effective strategies to improve the hydrogenation and dehydrogenation kinetics of MgH2 is the incorporation of transition metal catalysts. Nickel (Ni) and titanium (Ti) have shown significant catalytic effects, reducing the activation energy required for hydrogen release. For example, doping MgH2 with 5 wt% Ni has been observed to lower the desorption temperature from approximately 300°C to 250°C while improving absorption rates. Similarly, Ti-based additives, such as TiCl3 or TiO2, enhance surface reactivity by creating nucleation sites for hydrogen dissociation and recombination. These catalysts disrupt the stable MgH2 lattice, facilitating faster hydrogen diffusion and lowering the energy barrier for reversible reactions.

Ball-milling is a widely used mechanical technique to refine the microstructure of MgH2 composites. By subjecting MgH2 and catalyst mixtures to high-energy impacts, particle size is reduced to the nanometer scale, increasing surface area and shortening hydrogen diffusion pathways. Prolonged ball-milling can also introduce lattice defects and strain, further improving hydrogen uptake and release kinetics. Studies indicate that ball-milled MgH2 with 10 wt% Nb2O5 achieves 80% of its hydrogen capacity within 5 minutes at 300°C, compared to untreated MgH2, which requires hours under the same conditions. However, excessive milling may lead to particle agglomeration or contamination, necessitating optimization of processing parameters.

Nanostructuring techniques, such as thin-film deposition or templated synthesis, offer additional control over material properties. Confining MgH2 within carbon scaffolds or mesoporous matrices prevents particle coalescence during cycling and enhances thermal conductivity. Graphene-supported MgH2 composites, for instance, demonstrate improved cyclic stability due to the mechanical reinforcement and conductive pathways provided by the carbon network. These nanostructured systems can achieve reversible hydrogen storage at moderate temperatures (200–250°C) with minimal degradation over dozens of cycles.

Despite these improvements, trade-offs remain between gravimetric capacity, reversibility, and energy input. While catalyst doping and nanostructuring enhance kinetics, they often reduce the overall hydrogen storage capacity due to the added weight of non-hydrogen-containing materials. For example, a composite with 10 wt% catalyst may see its effective capacity drop from 7.6 wt% to below 6 wt%. Additionally, the energy required to maintain elevated temperatures for hydrogen release remains a challenge, particularly for applications where low-grade waste heat is unavailable.

In contrast to reversible chemical hydrides like MgH2, non-reversible hydrides such as lithium borohydride (LiBH4) or sodium alanate (NaAlH4) release hydrogen through irreversible or multi-step reactions, requiring chemical reprocessing to regenerate the storage material. While these systems can achieve higher hydrogen densities, their complexity and energy-intensive regeneration processes limit their practicality for stationary storage. Reversible hydrides like MgH2 offer a more sustainable solution, provided cycle life and operational temperatures are further optimized.

Applications of MgH2 composites are particularly suited to stationary hydrogen storage, where weight is less critical than volume and long-term stability. Integrated with renewable energy systems, these materials can store excess electricity from wind or solar sources via electrolysis, releasing hydrogen on demand for fuel cells or industrial use. Pilot projects have demonstrated the feasibility of MgH2-based storage units for microgrids, though challenges in scaling up production and ensuring consistent performance remain.

Cycle life is a critical hurdle for MgH2 composites, as repeated hydrogenation and dehydrogenation induce mechanical stress and phase segregation. Over time, catalyst particles may coarsen or migrate, reducing their effectiveness. Advanced encapsulation techniques and self-healing materials are under investigation to mitigate these effects. Preliminary results suggest that hybrid systems combining MgH2 with small amounts of complex hydrides, such as LiNH2, can improve longevity by stabilizing the microstructure during cycling.

In summary, magnesium hydride composites represent a significant step forward in reversible hydrogen storage technology. Through strategic catalyst doping, ball-milling, and nanostructuring, their kinetics and operating conditions have been markedly improved. While trade-offs in capacity and energy requirements persist, ongoing research aims to refine these materials for broader adoption in stationary storage applications. Compared to non-reversible hydrides, MgH2 offers a more sustainable and practical pathway for integrating hydrogen into the energy economy, provided challenges in cycle life and system integration are addressed.