Well-aligned TiO2 nanotube arrays for energy-related applications under solar irradiation

Titania nanotube arrays have attracted significant scientific interests due to the interrelation of material functional properties with a controllable nanostructure. Superior properties of well-aligned TiO2 nanotube arrays, such as vectorial pathway of e− transport, suppressed e− recombination, high reaction site and enhanced light scattering render them as the most promising candidate for solar harvesting applications. Photoelectrochemical cells (PECs) and dye-sensitized solar cells (DSSCs) based on TiO2 photoanodes have attracted great interests due to their outstanding potential to convert solar energy into clean and renewable energy. Performance of PECs and DSSCs is greatly determined by the structural morphology of nanotube arrays. In this contribution, the fabrication, properties and energy-related applications of TiO2 nanotube arrays have been reviewed by focusing on synthesis by anodization in fluoride-containing electrolyte. The effect of anodization process parameters, such as applied potential, pH, exposure time, electrolyte type and composition on structural morphologies of TiO2 nanotube arrays has been comprehensively discussed. Several strategies for the electronic structure modification of TiO2 nanotube arrays to efficiently harvest visible-light irradiation, including noble metal loading, metal doping, nonmetal doping, semiconductor composite and sensitization have also been reviewed.