Hydrogen storage technologies and materials: Progress, challenges, and paths towards a sustainable hydrogen economy

Hydrogen, with its high gravimetric energy density (≈120 MJ kg-1) and no carbon dioxide emissions from combustion or electrochemical oxidation, is a key element for decarbonization and the integration of renewable energy sources. However, its low volumetric density at ambient conditions (0.0899 kg m-3) requires efficient, safe, and economically acceptable storage solutions. This review paper synthesizes the latest methods for physical, solid-state, and geological hydrogen storage, drawing on advances in materials science and techno-economic assessment. Special emphasis is placed on the trade-offs among gravimetric/volumetric densities, efficiency, technology maturity, and scalability to guide technology selection for applications in transport, industry, and grid systems.