High-performance and renewable supercapacitors based on TiO2 nanotube array electrodes treated by an electrochemical doping approach

Although one-dimensional anodic TiO2 nanotube arrays have shown promise as supercapacitor electrode materials, their poor electronic conductivity embarrasses the practical applications. Here, we develop a simple electrochemical doping method to significantly improve the electronic conductivity and the electrochemical performances of TiO2 nanotube electrodes. These TiO2 nanotube electrodes treated by the electrochemical hydrogenation doping (TiO2-H) exhibit a very high average specific capacitance of 20.08 mF cm−2 at a current density of 0.05 mA cm−2, ∼20 times more than the pristine TiO2 nanotube electrodes. The improved electrochemical performances can be attributed to ultrahigh conductivity of TiO2-H due to the introduction of interstitial hydrogen ions and oxygen vacancies by the doping. The supercapacitor device assembled by the doped electrodes delivers a specific capacitance of 5.42 mF cm−2 and power density of 27.66 mW cm−2, on average, at the current density of 0.05 mA cm−2. The device also shows an outstanding rate capability with 60% specific capacitance retained when the current density increases from 0.05 to 4.00 mA cm−2. More interestingly, the electrochemical performances of the supercapacitor after cycling can be recovered by the same doping process. This strategy boosts the performances of the supercapacitor, especially cycling stability.