Limei Xu
International Centre for Quantum Materials and School of Physics, Peking University, Beijing, China
Ion hydration at interfaces is of great importance for an extremely wide range of applied fields and processes, including salt dissolution, corrosion, electrochemistry, biological ion channel, atmospheric aerosols and water desalination. One of the key issues is to uncover the microscopic factors that govern the transport of the interfacial hydrated ions, especially for the nanoconfined fluidic systems. In spite of massive experimental and theoretical efforts, the direct correlation between the atomic structure and the transport properties of the hydrated ions is still lacking. Combing experiment and simulations, we investigate the mobility of Na+ hydration clusters on a NaCl (001) surface in a well-controlled manner. We found that the Na+ hydrated with three water molecules diffuses orders of magnitude faster than other ion hydrates due to a peculiar collective rotation of three water molecules around the Na+ ion with an exceptionally small diffusion barrier. It suggests that there may exist a magic-number effect on the transport of interfacial hydrated ions, which is determined by the degree of symmetry match between the hydrates and the interface.