TiO Nanotubes with Laterally Spaced Ordering Enable Optimized Hierarchical Structures with Significantly Enhanced Photocatalytic H Generation

In the present work we grow self-organized TiO nanotube arrays with a defined and controlled regular spacing between individual nanotubes. These defined intertube gaps allow one to build up hierarchical 1D-branched structures, conformally coated on the nanotube walls using a layer by layer nanoparticle TiO decoration of the individual tubes, i.e. having not only a high control over the TiO nanotube host structure but also on the harvesting layers. After optimizing the intertube spacing, we build host-guest arrays that show a drastically enhanced performance in photocatalytic H generation, compared to any arrangement of conventional TiO nanotubes or conventional TiO nanoparticle layers. We show this beneficial effect to be due to a combination of an increased large surface area (mainly provided by the nanoparticle layers) with a fast transport of the harvested charge within the passivated 1D nanotubes. We anticipate that this type of hierarchical structures based on TiO nanotubes with adjustable spacing will find even wider application, as they provide an unprecedented controllable combination of surface area and carrier transport.