Interconnected 3D TiO₂ Nanoscaffolds from TiN Anodization Exhibiting Fast and Reversible Aqueous Cation Insertion

Titanium dioxide (TiO₂) nanoscaffold thin films consisting of interconnected 3D TiO₂ nano-structures with an ordered pore network are fabricated by anodization of titanium nitride (TiN) blanket layers in fluoride-less aqueous electrolytes. The cross-section of the nanoscaffold films resemble a layered TiO₂ structure supported by 2 nm wide vertical interconnections. The formation and subsequent release of N₂ gas from the oxidation of N^3- facilitates the formation of the ordered network of 2-10 nm wide pores, while the oxidation of Ti³⁺ creates the mesh-like TiO₂ structures around them. The TiO₂ interconnections give good electronic conductivity, and the connected pores allow access of the active sites in amorphous TiO₂ by electrolytes, resulting in a volumetric surface area enhancement of 540x per micron thickness of the film. The films exhibit high charge retention capacity in nonaqueous and even in aqueous electrolytes for a multitude of ions, as demonstrated during electron-coupled ion-insertion reactions for Li⁺, Na⁺, K^+, and Mg²⁺. The controlled and targeted growth of the oxide during anodization can further facilitate the formation of patterned structures on masked TiN substrates, making the material attractive for numerous electrochemical applications.