Perspectives and prospects of underground hydrogen storage and natural hydrogen

Hydrogen is considered the fuel of the future due to its cleaner nature compared to methane and gasoline. Therefore, renewable hydrogen production technologies and long-term, affordable, and safe storage have recently attracted significant research interest. However, natural underground hydrogen production and storage have received scant attention in the literature despite its great potential. As such, the associated formation mechanisms, geological locations and future applications remain relatively under-explored, thereby requiring further investigation. In this review, the global natural hydrogen formation along with reaction mechanisms (i.e., metamorphic processes, pyritization and serpentinization reactions) as well as the suitable geological locations (i.e., ophiolites, organic-rich sediments, fault zones, igneous rocks, crystalline basements, salt bearing strata, and hydrocarbon-bearing basins) are discussed. Moreover, the underground hydrogen storage mechanisms are detailed and compared with underground natural gas and CO2 storage. Techno-economic analyses of large-scale underground hydrogen storage are presented along with the current challenges and future directions.