Boosting Supercapacitor Performance of TiO2 Nanobelts by Efficient Nitrogen Doping

TiO2 has great potential in the application of biocompatible supercapacitors. Unfortunately, because of its semiconducting nature, TiO2 exhibits poor electrical conductivity and extremely low specific capacitance. Doping with other atoms is a facile way to enhance electrochemical activity of TiO2. However, the restricted solubility of substitutional dopants in bulk largely impaired the effectiveness of doping, resulting in quite limited capacitance improvement. To overcome this issue, we propose a two-step approach to efficiently dope TiO2 nanobelts with nitrogen. High-level nitrogen doping (6.1 at.%) was achieved in the distinct crystalline core/disordered shell structured TiO2, boosting the specific capacitance of TiO2 from 4 Fg(-1) to 216 Fg(-1). Employing compressible, light-weight three-dimensional graphene as current collector, the symmetrical cell exhibits a volumetric energy density of 9.6 mWh cm(-3), highly comparable with the supercapacitors based on conventional pseudocapacitive materials. These encouraging findings unambiguously smash the capacitance bottleneck of TiO2 and open the door towards the application of TiO2 in energy-storage systems.