Porous ice represents an emerging class of crystalline ice phases characterized by extensive nano-cavities and/or nano-channels within their hydrogen-bonded water frameworks. The prediction of ultralow-density porous ices is of particular interest, as their high surface-to-volume ratio could significantly expand their practical applications. In this work, we assembled two series of ultralow-density porous ices from polyhedral water cages and ice nanotubes, designated as SODₙ and LTAₙ, respectively. Their density decreases progressively with the increasing length of the constituent ice nanotubes. The SODₙ structures were predicted to be stable under negative pressure by first-principles calculations using the vdW-DF2 functional. By evaluating the mechanical stability of these porous ices, we reconstructed a new water phase diagram under negative pressure. Furthermore, the guest-assisted growth of the SOD framework and the formation of SODₙ (n = 1-4) were demonstrated by extensive molecular dynamics simulations. Notably, SOD₅, with a remarkably low density of 0. 2 g/cm3, exhibits promising gas storage performance at 100 bar and 77 K. Its predicted capacities are 36. 29 wt. % (105. 88 g/l) for H2 and 0. 65 g/g (489 cm3 STP/cm3) for CH4. These results demonstrate the potential of ultralow-density porous ice as a novel medium for gas storage.
Sun et al. (Thu,) studied this question.