Electrochemical tuning of heterojunctions in TiO 2 nanotubes for efficient solar water splitting

• Published in: Catalysis science & technology 2019-10, Vol.9 (19), p.5425-5432
• Main Authors: Preethi, L. K., Mathews, Tom
• Format: Article
• Language: English
• ISSN: 2044-4753; 2044-4761
• DOI: 10.1039/C9CY01216H

Biphase ↔ triphase switching in TiO 2 nanotubes is observed with the change in electrolyte concentration using the rapid breakdown anodization technique. The phase composition of TiO 2 nanotubes switches from anatase–rutile–brookite to anatase–brookite and vice versa . The tubular morphology of the samples is revealed from the SEM and TEM micrographs. All the phases are found to be present in a single nanotube, forming heterojunctions. The photocatalytic hydrogen generation efficiencies of TiO 2 nanotubes with anatase–rutile–brookite heterojunctions are compared with those of nanotubes having anatase–brookite (obtained by tuning the electrolyte concentration) and anatase–rutile heterojunctions (obtained from the same technique reported elsewhere). The higher water splitting efficiencies of triphasic heterojunctions compared to those of biphasic junctions are attributed to effective charge separation because of cascaded charge transfer through sequential heterojunctions. This leads to the accumulation of electrons and holes in the lowest conduction band and highest valence band levels, respectively, among the phases. The present study supports the theory that a triphasic system is more efficient in photocatalysis compared to two-phase systems. In addition, this study also reports that anatase–brookite biphasic TiO 2 is more efficient compared to the widely studied anatase–rutile biphasic TiO 2 for the first time.