Skin supersolidity matters the performance and functionality of water droplets.

Even more fascinating than its bulk parent, a water droplet possesses extraordinary catalytic and hydro‐voltaic capability, elastic adaptivity, hydrophobicity, sensitivity, thermal stability, etc., but the underlying mechanism is still elusive. We emphasize herewith that the H‒O bond follows the universal bond order‒length‒strength correlation and nonbonding electron polarization regulation and the hydrogen bond cooperativity and polarizability notion regulates the performance of the coupling hydrogen bond (O:H‒O). Computational and spectrometric evidence consistently shows that molecular undercoordination shortens the intramolecular H‒O bond by up to 10% while lengthening the intermolecular O:H nonbond by 20% cooperatively with an association of electron polarization, making the 0.3‐nm thick droplet skin of a supersolid phase of self‐electrification. The supersolid skin dictates the performance and functionality of the droplet in chemical, dielectric, electrical, mechanical, optical, and thermal properties as well as the transport dynamics of electrons and phonons. The amplification of these findings could deepen our insight into the undercoordinated aqueous systems, including bubbles and molecular clusters, and promote deep engineering of water and ice. [ABSTRACT FROM AUTHOR]