Orientation dependence of charge-transfer processes on TiO2 (anatase) single crystals

Electrochemical measurements in aqueous and aprotic media have been carried our on anatase single crystals with exposed (101) and (001) surfaces, respectively. Water reduction and photo-oxidation take place at more negative potentials for the (001) surface than for the (101) surface. This can be rationalized in terms of a more negative flatband potential (by cn. 0.06 V) for the (001) face, which is due to dissociative chemisorption of water molecules on this surface. Lithium insertion is favored on the (001) surface, as evidenced by a higher standard rats constant for charge transfer (10(-8) vs. 2 . 10(-9) cm/s) and a higher chemical diffusion coefficient for Lit insertion (4 . 10(-13) vs. 2 . 10(-13) cm(2)/s) for the propagation along the c axis. This can be explained by a more open structure of the anatase lattice in this direction. (C) 2000 The Electrochemical Society. S0013-4651(99)08-067-2. All rights reserved.