Topotactic conversion route to ultrafine crystalline TiO2 nanotubes with optimizable electrochemical performance

Abstract

Anatase TiO₂ nanotubes have been successfully synthesized via a topotactic chemical transformation from H₂Ti₃O₇ nanotubes, in which the primary H₂Ti₃O₇ nanotube frameworks can be preserved. The TiO₂ nanotubes have an average outer diameter of around 8 nm and the inner diameter around 3–4 nm with 2 micrometers in length. Importantly, the nanotubes' shells are mainly formed by (113) planes perpendicular to the long axial of nanotubes, which is different from the structures found in the literature. The electrochemical properties are investigated by constant current discharge/charge measurements. There are potential plateaus at 1.75 and 1.93V in the process of Li insertion and extraction of the TiO₂ nanotubes, and the initial Li insertion/extraction capacity is 590 and 298 mA h g⁻¹ at 30 mA g⁻¹, respectively. In the charge–discharge capacities of TiO₂ nanotubes (calcination at 500 °C) at different current rates, the reversible capacity still remains at about 165 and 139 mA h g⁻¹ at current density of 480 and 960 mA g⁻¹, respectively with excellent coulombic efficiency of approximately 100%.