A high-performance TiO2 nanotube supercapacitor by tuning heating rate during H2 thermal annealing

TiO2 nanotube is a promising material for supercapacitor electrodes. Thermal annealing has been proved as an effective way enhancing the performance of TiO2 nanotube supercapacitors. However, heating rate, as an important parameter in the thermal annealing, has been overlooked as a factor that can influence the electrochemical performance of TiO2 nanotube supercapacitors. In this paper, we demonstrate that the electrochemical performance of TiO2 nanotube supercapacitors fabricated by anodization process can be significantly improved by tuning heating rate during hydrogen thermal annealing. At the optimal condition, the areal capacitance of TiO2 nanotube supercapacitors increased from 27.36 to 52.40 mF cm(-2) with a scan rate of 100 mV s(-1), while maintaining a high capacitance retention of 65.9% when the scan rate increased from 10 to 1000 mV s(-1). Moreover, outstanding long-term cycling stability with only 4.8% capacitance reduction after 5000 charge-discharge cycles is observed. It is found that the electronic carrier densities, surface hydroxyl group density, as well as crystallite size in TiO2 are maximized at the optimal annealing condition, all of which are accounted for the enhancement of the electrochemical performance.