UiO-type metal - organic frameworks as a platform for hydrogen storage studies.

Hydrogen has attracted significant attention as a clean energy carrier due to its high gravimetric energy density and zero-carbon emissions at the point of use. However, its low volumetric energy density poses major challenges for safe and efficient storage. In this context, porous materials, particularly metal - organic frameworks (MOFs), have been extensively investigated as promising hydrogen-storage media because of their high surface areas, tunable pore environments, and structural diversity. Among them, Zr-based Universitetet i Oslo (UiO)-type MOFs have emerged as important platforms for hydrogen storage studies because of their exceptional framework stability, high synthetic versatility, and compatibility with the incorporation of functional species such as metal nanoparticles and hydrides. This review focuses on recent advances in hydrogen storage studies using UiO-type MOFs. First, the fundamental synthesis strategies and structural characteristics of UiO frameworks are outlined. Subsequently, key concepts of physisorption-based hydrogen storage, including adsorption mechanisms and evaluation metrics, are introduced. The hydrogen storage performance of pristine, functionalized, and densified UiO-type MOFs is then discussed, highlighting the influence of pore structure, linker functionality, and framework densification on hydrogen uptake. Beyond physisorption, chemisorption-related approaches, including spillover-assisted hydrogen storage and nanoconfinement of hydride species within UiO-type MOFs, are also highlighted. These studies demonstrate that UiO-type MOFs not only function as effective hydrogen adsorbents but also serve as versatile platforms for tuning hydrogen interactions. Finally, current challenges and future perspectives are discussed, providing insights into the development of next-generation hydrogen storage materials.