Establishing self-organized spacing between TiO₂ nanotubes allows for highly conformal wall decoration – allowing for spatially defined hierarchical structures that can be adjusted to an optimized electrochemical performance.

In the present work we grow self-organized TiO₂ 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 TiO₂ decoration of the individual tubes, i.e. having not only a high control over the TiO₂ 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 H₂ generation, compared to any arrangement of conventional TiO₂ nanotubes or conventional TiO₂ 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 TiO₂ nanotubes with adjustable spacing will find even wider application, as they provide an unprecedented controllable combination of surface area and carrier transport.