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.