  In this work we describe the synthesis and electrochemical properties of
nitridated hierarchical TiO$_2$ nanotubes as an electrode for supercapacitors.
The hierarchical TiO$_2$ nanostructures are formed by a controlled
layer-by-layer TiO2 nanoparticle decoration on self-organized spaced TiO$_2$
nanotubes. These structures are then annealed in NH$_3$ atmosphere at elevated
temperature to convert the material to a nitride structure -- this drastically
enhances their electron-transport properties. The areal capacitance of
hierarchical structures can be tuned by changing the number of decorated
TiO$_2$ nanoparticle layers. The capacitance enhancement of the hierarchical
structures reaches a maximum when the surface area through nanoparticle
deposition is highest and the conductivity via nitridation is optimized.
