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

Abstract

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 N3− 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.