Abstract
Hydrogen is one of the most promising options for future energy storage. Specifically, hydrogen produced from renewable sources is expected to play a central role in driving the green transition and reducing the global climate impacts. However, transportation and storage remain the most critical hurdles for the hydrogen economy due to hydrogen's inherently low density (0.0883 kg/m3 STP). Developing efficient storage technologies is therefore essential to enable seasonal and long-duration energy storage, with profound implications for the future energy landscape. Adsorption-based hydrogen storage continues to be of substantial interest as a potentially safe and low-cost solution for storage and transport. This review highlights the requirements for adsorption-based hydrogen systems and the chemistries and processes that hold promise in advancing the field. Both physisorbed and chemisorbed materials are emphasized as key areas of development. The main challenges lie in overcoming fundamental barriers to deliver novel materials and processes that achieve high energy density while remaining scalable, compact, and safe. Recent advances point to the design of composite materials that combine strong physisorption with weak chemisorption mechanisms to optimize storage performance. For physisorbents, promising synthetic strategies include doping and functionalization with catalytic nanoparticles, exploiting spillover effects, introducing nanopump-assisted interlayer spacing, and tailoring pore sizes. For chemisorbents, ongoing progress continues to improve storage capacity, reversibility, kinetics, and safety, paving the way toward optimized hydrogen storage systems for practical applications.