Abstract
This paper reviews the critical role of material qualification in enabling the safe, efficient, and long-term underground storage of hydrogen. As the global energy landscape shifts toward decarbonization, underground hydrogen storage (UHS) emerges as a vital technology for balancing renewable energy supply and demand. However, hydrogen presents challenges for subsurface containment and infrastructure integrity. This article discusses the main geological options for UHS, such as salt caverns, depleted hydrocarbon reservoirs, saline aquifers, and engineered rock caverns, outlining their suitability and operational challenges. Special attention is given to the risks posed by impurities generated through biogeochemical interactions in underground environments, which can lead to corrosion, embrittlement, and failure of steels and alloys used in storage systems. The need for rigorous material qualification, including evaluation of mechanical properties under realistic environmental and loading conditions, is emphasized, alongside strategies for mitigating the effects of contaminants like water and hydrogen sulphide. The work underlines the importance of ongoing research to guide material selection, system design, and operational protocols for robust and sustainable UHS deployment.