Self-ordering dual-layered honeycomb nanotubular titania: Enhanced structural stability and energy storage capacity

Electrochemical energy storage of TiO2 anodic oxide with a novel honeycomb morphology was characterized and compared with that of standard TiO2 nanotubes. The new morphology consists of several smaller-diameter (∼20 nm) nanotubes stacked inside of each honeycomb like hemisphere. The honeycomb like hemispheres are 160-200 nm in diameter with inter-wall thicknesses of 20-50 nm grown onto a planar barrier layer. The dual-layered honeycomb oxide has a total thickness of about 350-500 nm and high surface area. Cyclic voltammetry and galvanostatic charge-discharge tests were carried out on these oxide samples in as-anodized and thermally annealed conditions using 0.1 M NaOH and 0.1 M LiCl + 0.1 M HCl electrolytes. The honeycomb arrays showed an areal capacitance of 56 mF cm−2 at 100 mV s−1 scan rate, and 0.75 mF cm−2 at a current density of 0.1 mA cm−2. The areal capacitance of the honeycomb structured samples were about 60% higher than that of the regular TiO2 nanotubes. The honeycomb structured TiO2 also showed 33% higher capacitance retention after 10,000 cycles than that of regular TiO2 nanotubes. The higher capacitance retention could be attributed to the enhanced structural stability of the honeycomb structures.