Ordered Arrays of TiO2 Nanotubes and Nanorods

Several authors reported an occasional large water splitting photocurrent obtained with nanotube Ti02 array electrodes, which appears to be a complex function of the aforementioned geometrical features and should be critically affected by the crystallinity of the walls. This last point, in fact, plays an essential role in the separation of photogenerated charges and in the vectorial electron transport to the back contact. 

The latter example, as also apparently that of Ti02 nanotube array photoanodes, emphasizes the role played by the space charge layer in determining sizeable IPCEs for slow photo-oxidatiOTi reactions, in which intermediates or products able to act as scavengers for photogenerated electrons are formed. 

In view of the results reported to date, the Ti02 films doped with non-metallic elements offer rather poor prospects for application as effective sunlight-driven photoanodes for water splitting. As discussed earlier, the situation is quite different in the case of nitrogen- and especially carbon-doped titania powders which have been demonstrated to act as efficient visible-light active photocatalysts for the degradation of various organic pollutants. 

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