Synthesis and characterization of a coaxial carbon-TiO2 nanotube arrays film with spectral response from UV to NIR and its application in solar energy conversion

In this paper, a facile one-step vacuum annealing process has been developed to fabricate the coaxial carbon-TiO2 nanotube arrays (CC-TNAs) film. The obtained composite film is composed of TiO2 nanotubes self-doped by oxygen vacancies (V.os), and an ultrathin carbon layer covering on the outer wall of TiO2 nanotubes. This composite film exhibited high absorbency from UV to NIR wavelength region, high electric conductivity, and photothermal effect. As a photoanode for hydrogen generation, the film showed promising light response in Na2S/Na2SO3 aqueous solution under a broad wavelength range from UV to NIR wavelength region. The study of the working mechanism revealed that a unique non-stepped photocurrent was resulted from the photothermal effect of CC-TNAs film in the electrolyte environment. The performance of this photothermo-electrochemical (PTEC) process is determined by the co-existence of the V.os and the coaxial carbons of TNAs. This study provides new insight into the design, preparation, and correlation between the structure and performance for new semiconductor-carbon nanocomposites.