Ice floating on liquid water represents one of the anomalies of water. Although solids are typically denser than their liquids, ice is less dense than liquid water due to its intrinsic porosity that arises from the regular cavities of the water lattice. Such molecular porosity of ice holds great promise for trapping gas molecules as an efficient means of energy storage and CO 2 sequestration. Gas encapsulated in the water lattice presents a paradox. This is because nonpolar gases do not mix with liquid water, but they can incorporate massively into the solid lattice of water, yielding intriguing gascarrying water structures called gas hydrates with the gas density up to ~5 wt% for hydrogen, ~15 wt% for methane, and 30 wt% for CO 2 . In nature, methane-bearing water structures, known as natural gas hydrates, occur abundantly in subsea and permafrost sediments and lock multi-trillion tons of solidified methane. Natural gas hydrates showcase the unparalleled potential of gas-carrying water structures for large-scale energy storage and CO 2 sequestration, taking the advantages of water as a sustainable feedstock (Fig .