A New Supercritical Phase and Fast Transport of Water in Two-Dimensions

Water structure and dynamics in confinement systems differ significantly from those in the bulk phase. Here, we report a new supercritical (SC) phase of water found in a 0.65 nm Au nanoslit. In this SC water, two metastable phases coexist, one shows solid-like (SL) behavior and the other is liquid-like (LL). Through calculating the isotherms in the "pressure-volume" plane, the critical point is determined to be at (T_c/K, P_c/MPa) = (262 ± 2, 14 ± 2). Under biased pressure, the LL domain can form a quick flow in the hydrophilic Au nanoslit, challenging the conventional wisdom that fast water transport can only occur in a hydrophobic environment. Instead, our results suggest that undercoordination is the key factor for efficient water transport. These findings contribute to a better understanding of the complicated water phase diagram and could find industrial potential for water treatment.