Underground energy storage: Key scientific challenges and frontier directions in the energy transition

The intermittency and volatility of renewable energy sources critically constrain their large-scale grid integration, positioning underground energy storage as an indispensable solution for the energy transition. This editorial provides a comprehensive overview of major underground energy storage technologies-including salt cavern compressed air energy storage, depleted gas reservoir storage, underground hydrogen storage, geological CO₂ sequestration, and underground thermal energy storage. For each modality, we identify key challenges such as multi-physics coupling, caprock integrity, geochemical reactivity, and long-term reservoir stability. We further highlight cross-cutting frontiers including digital rock physics, artificial intelligence-driven characterization, and digital twin technologies. Finally, we issue a formal call for contributions that bridge fundamental mechanisms with field-scale engineering practice, reaffirming the commitment of Advances in Geo-Energy Research to advancing geo-energy science for a sustainable future.