Magnesium-Based Hydrides and High-Entropy Alloys: A Review of Advancements and Pathways for Next-Generation Hydrogen Storage Materials

The increase in global emissions, primarily from the burning of fossil fuels, has created an urgent need for green energy solutions. Hydrogen holds significant promise as a clean energy alternative, due to its potential to reduce greenhouse gas emissions. However, hydrogen storage faces a major hurdle, impeding its widespread use. This is because traditional high-pressure gas or cryogenic liquid storage methods are inefficient, bulky, and pose safety risks. Solid-state hydrogen storage using metal hydrides offers a safer and more compact alternative by chemically bonding hydrogen within the solid material. This allows for higher storage density at lower pressures and moderate temperatures. However, challenges with solid-state storage persist due to difficulty in achieving onboard storage capacity and meeting practical requirements. Magnesium hydride (MgH 2 ) remains one of the most promising solid-state hydrogen storage materials, offering 7.6 wt.% gravimetric capacity. However, its high thermodynamic stability and slow sorption kinetics restrict practical application. This review presents a comprehensive and critically integrated analysis of strategies to overcome these limitations: alloying, catalytic doping, nanostructuring, metastable phase engineering, and destabilization with complex hydrides. Mg-containing complex concentrated alloys (CCAs) and high-entropy alloys (HEAs) are examined as an emerging design paradigm that leverages configurational entropy to tune thermodynamic and kinetic properties. The roles of CALPHAD, density functional theory, and machine learning in accelerating alloy design are critically assessed. This review identifies both compositional and computational as concrete pathways toward next-generation Mg-based hydrogen storage materials capable of meeting practical requirements.