Cryogenic stabilization of molecular hydrogen in dense cubic ice
Hydrogen is widely regarded as a cornerstone of future low-carbon energy technologies, yet the lack of safe, efficient, and reversible solid-state storage materials remains a major barrier to its large-scale deployment. Although porous frameworks and metal hydrides have been extensively explored, far less is known about the ability of dense molecular solids to stabilize hydrogen at near-ambient pressure. Here we show that fully crystalline cubic ice, despite its non-porous nature, can retain molecular hydrogen as an interstitial guest following controlled decompression from a high-pressure hydrogen hydrate precursor. Using synchrotron X-ray diffraction, neutron diffraction, and Raman spectroscopy, we demonstrate that hydrogen is retained within the ice structure up to about 130 K, producing reproducible lattice expansion and distinct spectroscopic signatures. We further show that pure cubic ice can be partially refilled with hydrogen at 0.18 GPa and 130 K, while fully hydrogen-filled cubic structure can be preserved at the same pressure up to 90 K. The retained hydrogen content reaches several percent of the parent hydrate composition, corresponding to gravimetric and volumetric storage densities comparable to those of interstitial hydrogen in metals. These results reveal an unexpected ability of a dense hydrogen-bonded crystal structure to host molecular hydrogen without permanent porosity or chemical bonding, establishing cubic ice as a minimal model for hydrogen-lattice interactions. More broadly, our findings identify dense hydrogen-bonded solids as an unexplored class of materials for hydrogen storage physics, with implications extending from energy materials to planetary and astrophysical ice environments.