Ar+-ion bombardment of TiO2 nanotubes creates co-catalytic effect for photocatalytic open circuit hydrogen evolution

In the present work, extended Argon ion bombardment was used to modify anatase TiO2 nanotube (NT) layers. In situ X-ray photoelectron spectroscopy revealed that a high content of sub-oxide was formed (Ti3 +, Ti2 + states) in the nanotube layers. These samples were tested for their ability to show open-circuit photocatalytic hydrogen evolution. We found for UV illumination (cw laser 325 nm) as well as for AM1.5 conditions, a strongly enhanced H2 evolution activity in the absence of the usual noble metal-nanoparticle decoration. We conclude therefore that these sub-oxide states can play an important role in the activation of TiO2 nanotubes - namely as a H2 evolution co-catalyst.