Proton Transport through Ice Nanoribbons

Water in confined geometries exhibits unusual static and dynamic properties. Here, we revealed proton transport through water confined in distorted single-wall carbon nanotubes (SWCNTs) by means of molecular dynamics (MD) simulations. The proton transport properties of the confined water were found to be controlled by the distortion ratio of the SWCNTs, where the SWCNTs were uniaxially compressed in a direction perpendicular to the SWCNT axes. In the appropriately distorted SWCNTs, the confined water forms an ice nanoribbon with a finite width perpendicular to the tube axis. An excess proton was found to diffuse preferentially along the edge water molecules of the ice nanoribbon via the Grotthuss mechanism. The mobility of the excess proton sensitively depends on the structure, especially the O-O-O bond angle θ_OOO, of the edge water molecules in the ice nanoribbons, and it exhibits a maximum value when θ_OOO ∼ 146°. The mechanism of proton transport through the ice nanoribbons might have important implications for the development of novel proton exchange membranes for fuel cells, as well as for better understanding the mechanisms of proton transport through biological membranes.