posted on 2011-05-25, 00:00authored byJung-Ho Yun, Yun Hau Ng, Changhui Ye, Attila J. Mozer, Gordon G. Wallace, Rose Amal
This work reports the use of sodium fluoride (in ethylene glycol
electrolyte) as the replacement of hydrofluoric acid and ammonium
fluoride to fabricate long and perpendicularly well-aligned TiO2 nanotube (TNT) (up to 21 μm) using anodization. Anodizing
duration, applied voltage and electrolyte composition influenced the
geometry and surface morphologies of TNT. The growth mechanism of
TNT is interpreted by analyzing the current transient profile and
the total charge density generated during anodization. The system
with low water content (2 wt %) yielded a membrane-like mesoporous
TiO2 film, whereas high anodizing voltage (70 V) resulted
in the unstable film of TNT arrays. An optimized condition using 5
wt % water content and 60 V of anodizing voltage gave a stable array
of nanotube with controllable length and pore diameter. Upon photoexcitation,
TNTs synthesized under this condition exhibited a slower charge recombination
rate as nanotube length increased. When made into cis-diisothiocyanato-bis(2,2̀-bipyridyl-4,4̀-dicarboxylato)
ruthenium(II) bis (tetrabutyl-ammonium)(N719) dye-sensitized solar
cells, good device efficiency at 3.33 % based on the optimized TNT
arrays was achieved with longer electron time compared with most mesoporous
TiO2 films.