Pulsed laser-induced photopotentials at the cobalt-photosensitized ZnO/electrolyte interface

Abstract

The time-resolved photoelectrochemical behavior of Co 2+-photosensitized ZnO electrodes is investigated in the 10 −8−10 −2 s time domain using the pulsed laser-induced photopotential technique. The influence of various parameters, such as the excitation wavelength (365 or 640 nm), the open-circuit prepolarization potential, the presence of hydroquinone as a reducing agent in the electrolyte, as well as the electrode surface pretreatment is analysed qualitatively. Although the Co 2+:3 d 7 ions extend the ZnO photoresponse to the whole visible range when they occupy the tetrahedral position inside the lattice, they are shown to induce e −- h + recombinations which develop within multiple successive time domains and originate from either the surface or the depletion region of the electrode. The similar kinetic behavior of the ZnO:Co/electrolyte interface when excited in the UV (band-to-band transitions) or the visible (Co 2+:3 d 7 intra-ionic transitions) range, suggests that the photocarriers are always under control of the ZnO structure.