Control of metal oxides' electronic conductivity through visual intercalation chemical reactions

Cation intercalation is an effective method to optimize the electronic structures of metal oxides, but tuning intercalation structure and conductivity by manipulating ion movement is difficult. Here, we report a visual topochemical synthesis strategy to control intercalation pathways and structures and realize the rapid synthesis of flexible conductive metal oxide films in one minute at room temperature. Using flexible TiO₂ nanofiber films as the prototype, we design three charge-driven models to intercalate preset Li⁺-ions into the TiO₂ lattice slowly (µm/s), rapidly (mm/s), or ultrafast (cm/s). The Li⁺-intercalation causes real-time color changes of the TiO₂ films from white to blue and then black, corresponding to the structures of Li_xTiO₂ and Li_xTiO_2-δ, and the enhanced conductivity from 0 to 1 and 40 S/m. This work realizes large-scale and rapid synthesis of flexible TiO₂ nanofiber films with tunable conductivity and is expected to extend the synthesis to other conductive metal oxide films.