Water-photolysis properties of micron-length highly-ordered titania nanotube-arrays

We report the water photoelectrolysis and photoelectrochemical properties of the titania nanotube arrays as a function of nanotube crystallinity, length (up to 6.4 mu m), and pore size. Most noteworthy of our results, under 320-400 nm illumination (98 mW/cm(2)) the titania nanotube-array photoanodes (area 1 cm(2)), pore size 110 nm, wall thickness 20 nm, and 6 Am length, generate hydrogen by water photoelectrolysis at a rate of 7.6 mL/hr, with a photoconversion efficiency of 12.25%. The energy-time normalized hydrogen evolution rate is 80 mL/hrW, the largest reported hydrogen photoelectrolysis generation rate for any material system by a factor of four, The highly-ordered nanotubular architecture appears to allow for superior charge separation and charge transport, with a calculated quantum efficiency of over 80% for incident photons with energies larger than the titania bandgap.