Titania nanofibers as a photo-antenna for dye-sensitized solar hydrogen

Directionally grown TiO2 nano-architectures can serve as effective platforms for photogenerated charges to flow vectorially through the architecture framework, promising an unexpectedly high efficiency. This study demonstrates that directionally aligned TiO2 nanofibers (TNF) obtained via a simple rearrangement of randomly scattered TiO2 nanoparticles (TNP) exhibit significantly enhanced activity in terms of hydrogen production from water under visible light (λ > 420 nm). It has been found that Eosin Y (EY)-sensitized hydrogen production with TNF is greater than those with TNP and commercial TiO2 samples (Degussa P25 and Hombikat UV-100) by a factor of 7 and >140, respectively, in the presence of triethanolamine (TEOA) as an electron donor. The annealing of TNF at elevated temperatures reduces the amount of H2 produced and changes various physicochemical properties. Attempts have been made to find correlation factors between hydrogen production and reaction parameters (e.g., pH-dependent EY adsorption, surface area, pore size, particle size, and anatase-to-rutile ratio), none of which have provided an apparent correlation. It was suggested that the interparticle electron transfer is facilitated when TiO2 nanoparticles are physically interconnected, and TNF might work as a robust photo-antenna for efficiently collecting the photogenerated electrons. The photocurrent measurements in visible light-irradiated EY/TiO2 suspensions indicate that the photocurrent of TNF is 50% higher than that of TNP, supporting the photo-antenna mechanism of TNF.