Highly Conducting Spaced TiO2 Nanotubes Enable Defined Conformal Coating with Nanocrystalline Nb2O5 and High Performance Supercapacitor Applications
Abstract
In this work, we report on the electrochemical behavior of nitrided spaced TiO2 nanotubes conformally coated with a nanocrystalline Nb2O5 layer and find for these hierarchical structures an excellent supercapacitor performance. Highly aligned conductive 1D electrodes were obtained by a three step process: i) growth of self-organized nanotubes with defined and adjustable intertube spacing, ii) conformal Nb2O5 decoration in the tube interspace (while providing full electrolyte access to the entire active area), and iii) high temperature nitridation. Key is the growth of a nanotube array with regular tube-to-tube interspacing that enables an optimized decoration with secondary materials such as Nb2O5. We observe an increase in electrode capacitance from 158 μF cm-2 for bare TiO2 NTs, to 1536 μF cm-2 for TiO2/Nb2O5 NTs, to finally 37 mF cm-2 for Nb2O5 decorated and then nitrided nanotubes. This drastic increase can be ascribed firstly to the defined spacing established between the tube arrays that then allows for a conformal coating with a secondary active coating. Secondly, nitridation causes a drastic increase of the electron conductivity of the entire scaffold and thus reduces resistive losses.