Time- and Frequency-resolved Photoelectrochemical Investigations on Nano-honeycomb TiO<sub>2</sub> Electrodes

Time- and frequency-resolved photoelectrochemical studies have been performed on nano-honeycomb porous TiO2 electrode prepared by photoelectrochemical etching of single crystal TiO2, both for its bare surface and when sensitized by cis-di(thiocyanato)-N,N-bis(2,2’-bipyridyl-4,4’-dicalboxylate)ruthenium(II). Since the remaining wall in the porous layer become as thin as the double thickness of the space charge layer by photoetching, electron diffusion comes to play the main role in the charge transport rather than field-driven migration. Intensity modulated photocurrent spectroscopy revealed much faster electron diffusion in the honeycomb electrode than that in colloid based porous electrode, because of the smaller electron trap density in the nano-honeycomb structure owing to the nonexistence of grain boundaries.