Branched titania nanotubes through anodization voltage control

Titania nanotubes are attractive for many applications such as energy generation, storage and delivery, gas sensing, and water purification. Here, we demonstrate branched titania nanotube formation during potentiostatic anodization of titanium films or foils in a single electrochemical bath by stepping down the anodization voltage Vanod below a threshold value. The linear dependence on the titanium nanotube diameter with Vanod and the lack of nanotube formation for Vanod < 20 V constrains homogeneous branching to occur only V2≤V12−V0, where V1 and V2 are the initial and final anodization voltages and V0 is a voltage offset dependent on the anodization bath chemistry. Our technique circumvents the constraints of multi-bath and multi-temperature methods for branching, and provides a versatile means for creating hierarchically sized and/or interconnected titania nanotubes for applications.