Blue $TiO_2$ nanotube arrays as semimetallic materials with enhanced photoelectrochemical activity towards water splitting

Abstract

In the past years there has been a great interest in self-doped $TiO_2$nanotubes (blue $TiO_2$ nanotubes) compared to undoped ones owing to their high carrier density and conductivity. In this study, blue $TiO_2$ nanotubes are investigated as photoanode materials for photoelectrochemical water splitting. Blue $TiO_2$ nanotubes were fabricated with enhanced photoresponse behavior through electrochemical cathodic polarization on undoped and annealed $TiO_2$ nanotubes. The annealing temperature of undoped $TiO_2$ nanotubes was tuned before cathodic polarization, revealing that annealing at 500 °C improved the photoresponse of the nanotubes significantly. Further optimization of the blue $TiO_2$ nanotubes was achieved by adjusting the cathodic polarization parameters. Blue $TiO_2$ nanotubes obtained at the potential of –1.4 V (vs. SCE) with a duration of 10 min exhibited twice more photocurrent response (0.39 mA cm–2) compared to the undoped $TiO_2$ nanotube arrays (0.19 mA cm–2). Oxygen vacancies formed through the cathodic polarization decreased charge recombination and enhanced charge transfer rate; therefore, a high photoelectrochemical activity under visible light irradiation could be achieved.