Physical solutions for hydrogen storage: Technological challenges, safety assessments, and environmental aspects

Hydrogen is a crucial energy vector for sustainable and low-carbon systems; however, storage and safety challenges limit its broader adoption. The paper comprehensively reviews the physical hydrogen storage technologies, focusing on safety features and environmental impacts as research gaps. It critically examines pressure- and temperature-based storage, material-based storage, and Underground Hydrogen Storage (UHS), evaluating their safety concerns, scientific challenges, and technological advancements. Pressure- and temperature-controlled methods involve storing hydrogen in compressed gas, liquid, or cryo-compressed forms. A novel classification of material-based storage is introduced, encompassing hydrate-based hydrogen storage, Hollow Glass Microspheres (HGMs), and adsorption methods. Large-scale seasonal hydrogen storage in subsurface geological formations, such as salt caverns, depleted hydrocarbon reservoirs, aquifers, and hard rock caverns, is also explored. Challenges and future directions of each storage method are analyzed to guide research toward safer and more efficient hydrogen storage solutions. The study also combines a systematic safety risk assessment with Life Cycle Assessment (LCA). Material-based storage shows promising safety but remains at an early development, whereas pressure- and temperature-based storage dominates the industry despite higher risks. UHS offers large-scale and long-term potential but faces geological and environmental challenges. LCA results indicate that compressed hydrogen has modest energy and emissions, whereas liquefied and cryo-compressed options impose the highest burdens. Material-based approaches show high energy demand and a wide uncertainty. UHS yields the lowest operational energy use, though construction and cushion gas dominate their life-cycle impacts. However, no single technology is universally optimal for all applications, necessitating further research to enhance efficiency and feasibility.