{001} Faceted Anatase Titanium Dioxide Crystals Photoanode for Solar Cells and Photocatalysis

Abstract

Performance of nanocrystal photocatalysts depends on not only their size, shape, composition, crystal phase, but also crystal facets. For anatase TiO2 crystals, the {001} faceted crystal surface possesses superior photocatalytic activity, highly attractive for degradation of organic pollutants, solar fuel production and solar energy conversion applications. A considerable research interest has arisen over recent years primarily driven by the demand for synthetic methods capable of producing anatase TiO2 crystals with high percentage of exposed {001} facets. However, the growth of anatase TiO2 crystals with exposed {001} facets dominated surface has been regarded as thermodynamically unfavourable due to its high surface energy (0.90 J/m2) relative to other anatase crystal facets such as {100} and {101} facets. A recently reported breakthrough [1] demonstrated that surface fluorination can dramatically reduce the {001} faceted surface energy to a level lower than that of the {101} faceted surface, producing anatase TiO2 single crystals with 47% exposed {001} facets. This concept has now been widely applied to obtain TiO2 crystals with higher percentages of exposed {001} facets. Herein, we report a series of facile liquid [2-4] and vapour [5-7] phase hydrothermal methods to control growth anatase TiO2 crystals with exposed {001} facets. The mechanisms of control growth {001} facets under liquid and vapour phases are investigated in details. The resultant {001} faceted anatase TiO2 crystals have been used as the photoanode for water oxidation and dye sensitised solar cells.