Lessons from Nature’s Freeze Crystallization-Perennial Sea Ice as a Model for Efficient Salt Rejection in Desalination

Desalination remains essential for combating global water scarcity, yet conventional thermal and membrane methods are fundamentally constrained by excessive energy demands, operational complexity, and environmental trade-offs. Inspired by natural salt expulsion in perennial sea ice, this work revolutionizes freeze-melt desalination (FMD) by establishing nano/micron-scale ice crystallization kinetics as the critical determinant of ultrapure water yield. We demonstrate that a quasi-comb-shaped columnar saltwater ice (qCSCSI) microstructure, featuring orthogonally aligned brine channels within horizonal c-axis monocrystalline ice, drives spontaneous solute rejection via curvature-dominated interfacial thermodynamics. Submicron ice-front control (r < 1 μm) minimizes brine trapping through synergistic Gibbs–Thomson confinement (Γ ≈ 29.7 K μm), ultralow interfacial viscosity (ηeff ≪ 1 mPa s), and kinetic supercooling dynamics (ΔT > −0.014 K), synergistically optimizing growth velocities (vn < 263 μm/s) for maximal salt rejection. Resolving FMD's energy bottleneck, ambient cold harvesting transforms system energetics: polar qCSCSI-FMD leverages cryospheric cycles (specific consumption ≈ 20.06 kWh/m3), while nonpolar designs exploit radiative/convective cooling inspired by cave ice formations. This dual innovation, bioinspired crystallization control coupled with passive cryogenic energy utilization, eliminates energy-intensive refrigeration and mechanical separation requirements, establishing qCSCSI-FMD as a scalable, low-carbon solution closing the water-energy nexus for sustainable security.