Kirkendall approach to the fabrication of ultra-thin ZnO nanotubes with high resistive sensitivity to humidity.

Ultra-thin ZnO nanotubes with an inner diameter of ∼3 nm and an outer diameter of ∼13 nm have been prepared via Kirkendall effect for the first time. The synthetic process was started from ultra-thin Zn nanowires, which were subjected to direct oxidation to form Zn-ZnO core-shell tubular nanostructures with continuous expansion of Kirkendall voids, and finally evolve into the ZnO nanotubes. The ultra-thin ZnO nanotubes have shown unusually high sensitivity to humidity in a resistive sensor mode, which can be attributed to not only the high specific surface areas, but more importantly, the overlapped electric double layers in the nanoscale channels with a significantly enhanced proton conductivity. This new type of proton conductive nanomaterials has important implications in the development of membranes in modern fuel cells among others.