Titania Nanotubes by Electrochemical Anodization for Solar Energy Conversion

TiO 2 nanotube arrays (NTs) are a promising platform for the conversion of sunlight to electricity in photovoltaic systems or to fuels in photoelectrochemical solar cells. We overview the properties and functionality of the various components of TiO 2 NT-based devices, discuss their integration in the energy conversion system and summarize recent advances in the field. In particular, we discuss the electronic and charge transport properties of TiO 2 NTs that govern the device performance and efficiency. Since the main challenge for the practical use of TiO 2 is the inability to absorb visible light, particular attention is paid to available techniques for TiO 2 sensitization, extending absorption beyond the UV portion of the solar spectrum. These techniques include doping to alter the bandgap and pairing TiO 2 with dyes, inorganic narrow band-gap semiconductors, or metal nanoparticles that exhibit plasmonic behavior. Various catalysts have been successfully paired with TiO 2 to accelerate the photocatalytic reactions of interest; materials, synthesis methods and catalytic mechanisms will also be discussed. Finally, we give a prospective outlook on the future of TiO 2 nanotubes for photoelectrochemical applications and identify areas for future research.