Enlarged capacitance of TiO₂ nanotube array electrodes treated by water soaking

Anodic TiO₂ (ATO) nanotube arrays have been considered as promising electrode materials for super capacitors. However, their specific capacitance value is still not comparable with conventional super capacitor materials. Here, we demonstrate a convenient method for improving the capacitive properties of ATO nanotube arrays for super capacitors, which can be realized simply by soaking the as-anodized ATO nanotube arrays in water at room temperature for a sufficiently long time. The nanotube wall for the soaked ATO nanotube arrays becomes rough, resulting in increased specific surface area. After an electrochemical hydrogenation doping process using potentiodynamic cycling for the ATO samples, the soaked ATO electrodes exhibit a very high average specific capacitance of 20.96 mF cm⁻² at a current density of 0.05 mA cm⁻², about a threefold improvement over those unsoaked ones that just treated by the electrochemical hydrogenation doping. The presented results demonstrate that the soaking treatment is a facile and cost-effective way to change the morphology of ATO nanotubes and increase specific capacitance, which would be of great industrial interest.