Reduced TiO2 nanotube arrays for photoelectrochemical water splitting

We report a facile one-step chemical method to synthesize partially reduced TiO2 nanotube arrays (NTAs). The NaBH4 treatment introduces oxygen vacancies on the surface and interior of TiO2. Oxygen vacancy extends the photocatalytic activity of TiO2 NTAs from the UV to visible light region, and enhances the electrical conductivity as well as charge transportation. Surface oxygen vacancies serve as charge carrier traps as well as adsorption sites where the charge transfer to adsorbed species inhibits the surface charge recombination, whereas bulk oxygen vacancies tend to act as charge carrier traps where e–h recombination occurs. The optimally reduced TiO2 NTAs yield a photocurrent density of 0.73 mA cm−2 at…