Thermodynamic destabilization of the hydrides of Mg-based hydrogen storage materials: A critical review

Magnesium hydride is a promising candidate for lightweight hydrogen storage due to its high gravimetric and volumetric capacities. However, the significant enthalpy of hydride formation (∼75 kJ/mol) results in a low equilibrium pressure under standard conditions, and the slow kinetics further limit its practical applications. This review presents a critical analysis of the three primary strategies employed to modify the reaction enthalpy (ΔH) of Mg-based materials, with the goal of engineering the operational temperature: alloying, nanostructure/interfacial engineering, and the formation of reactive hydride composites (RHCs). Each strategy offers a distinct pathway to thermodynamic destabilization. Alloying with elements such as nickel or silicon creates new, less stable metal hydrides and changes the other properties. Nanostructuring leverages the significant contributions of surface and interface energy at the nanoscale, which can alter reaction thermodynamics without compromising intrinsic capacity. Finally, RHCs fundamentally alter the chemical reaction pathway by combining MgH₂ with other hydrides, yielding stable products upon dehydrogenation that provide a strong thermodynamic driving force for hydrogen release. This review synthesizes progress made and highlights the collective significance of these materials in advancing magnesium-based materials toward practical hydrogen-storage applications.