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 m), and pore size. Most noteworthy of our results, under 320–400 nm illumination (98 mW/cm²) the titania nanotube-array photoanodes (area 1 cm²), pore size 110nm, wall thickness 20nm, and 6 m 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 80mL/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.