Black TiO₂ Nanotubes: Cocatalyst-Free Open-Circuit Hydrogen Generation

Here we report that TiO₂ nanotube (NT) arrays, converted by a high pressure H₂ treatment to anatase-like “black titania”, show a high open-circuit photocatalytic hydrogen production rate without the presence of a cocatalyst. Tubes converted to black titania using classic reduction treatments (e.g., atmospheric pressure H₂/Ar annealing) do not show this effect. The main difference caused by the high H₂ pressure annealing is the resulting room-temperature stable, isolated Ti³⁺ defect-structure created in the anatase nanotubes, as evident from electron spin resonance (ESR) investigations. This feature, absent for conventional reduction, seems thus to be responsible for activating intrinsic, cocatalytic centers that enable the observed high open-circuit hydrogen generation

“Black” TiO₂ Nanotubes Formed by High-Energy Proton Implantation Show Noble-Metal-<i>co</i>-Catalyst Free Photocatalytic H₂‑Evolution

We apply high-energy proton ion-implantation to modify TiO₂ nanotubes selectively at their tops. In the proton-implanted region, we observe the creation of intrinsic cocatalytic centers for photocatalytic H₂-evolution. We find proton implantation to induce specific defects and a characteristic modification of the electronic properties not only in nanotubes but also on anatase single crystal (001) surfaces. Nevertheless, for TiO₂ nanotubes a strong synergetic effect between implanted region (catalyst) and implant-free tube segment (absorber) can be obtained