Analysis of the transient photocurrent-time behaviour of a sintered n-SrTiO3 electrode in water photoelectrolysis

The transient photocurrent-time behaviour shown by a sintered n-SrTiO3 photanode during water photoelectrolysis has been studied. A model based on the existence of surface states in the bandgap region, generated by illumination, is supported by the experimental results. At sufficiently low band bending these surface states can be filled with conduction band electrons giving rise to a back-reaction opposed to the anodic photocurrent, which results in a photocurrent transient. Furthermore photogenerated holes can be trapped by intrinsic surface states, producing a decrease of the negative surface charge, and consequently a positive shift of the flat-band potential, which also decreases the photocurrent efficiency. The nature of the surface states involved in these photocurrent transients and their implication in the quantum efficiency of the system are discussed. The conclusions reached are applicable to n-TiO2 and probably to other semiconducting oxide photoanodes.