Electrochemical investigation of traps in a nanostructured TiO2 film

Electron traps at the nanostructured TiO2 (anatase)/aqueous electrolyte interface have been studied by means of electrochemical methods. The transient current decays at different potentials positive of the flat band potential clearly illustrate the trap-filling process. The more negative the potential, the shorter the trap-filling period. It is found that most traps locate positive of -0.9 V vs Ag/AgCl at pH 13, or positive of -0.3 V vs Ag/AgCl at pH 4.7. It is proposed that the trap distribution as a function of potential is directly proportional to dQ/dU, i.e., to the current density in a linear sweep voltammetry experiment. The trap densities in aqueous electrolytes are estimated to be 4 x 10(11) cm(-2) (microscopic area) at pH 4.7 and 5 x 10(13) cm(-2) (microscopic area) at pH 13. The pH dependency of the trap density indicates that traps investigated are surface-related.