Hydrogenated TiO2 Nanotube Arrays for Supercapacitors

We report a new and general strategy for improving the capacitive properties of TiO2 materials for supercapacitors, involving the synthesis of hydrogenated TiO2 nanotube arrays (NTAs). The hydrogenated TiO2 (denoted as H-TiO2) were obtained by calcination of anodized TiO2 NTAs in hydrogen atmosphere in a range of temperatures between 300 to 600 degrees C. The H TiO2 NTAs prepared at 400 degrees C yields the largest specific capacitance of 3.24 mF cm(-2) at a scan rate of 100 mV s(-1), which is 40 times higher than thecapacitance obtained from air-annealed TiO2 NTAs at the same conditions. Importantly, H-TiO2 NTAs also show remarkable rate capability with 68% areal capacitance retained when the scan rate increase from 10 to 1000 mV s(-1), as well as outstanding long-term cycling stability with only 3.1% reduction of initial specific capacitance after 10 000 cycles. The prominent electrochemical capacitive properties of H-TiO2 are attributed to the enhanced carrier density and increased density of hydroxyl group on TiO2 surface, as a result of hydrogenation. Furthermore, we demonstrate that H-TiO2 NTAs is a good scaffold to support MnO2 nanoparticles. The capacitor electrodes made by electrochemical deposition of MnO2 nanoparticles on H-TiO2 NTAs achieve a remarkable specific capacitance of 912 F g(-1) at a scan rate of 10 mV s(-1) (based on the mass of MnO2). The ability to improve the capacitive properties of TiO2 electrode materials should open up new opportunities for high-performance supercapacitors.