  Self-standing TiO$_2$ nanotube layers in the form of membranes are fabricated
by self-organizing anodization of Ti metal and a potential shock technique. The
membranes were then decorated by sputtering different Pt amounts i) only at the
top, ii) only at the bottom or iii) at both top and bottom of the tube layers.
The Pt-decorated membranes are transferred either in tube top up or in tube top
down configuration onto FTO slides and investigated after crystallization as
photocatalysts for H$_2$ generation using either front or back-side light
irradiation. Double-side Pt-decoration of the tube membranes leads to higher
H$_2$ generation rates (independent of tube and light irradiation
configuration) compared to membranes decorated at only one side with similar
overall Pt amounts. The results suggest that this effect is not ascribed to the
overall amount of Pt cocatalyst as such but rather to its distribution at both
tube extremities. This leads to optimized light absorption and electron
diffusion/transfer dynamics: the central part of the membranes act as light
harvesting zone and electrons therein generated can diffuse towards the
Pt/TiO$_2$ active zones (tube extremities) where they can react with the
environment and generate H$_2$ gas.
