Photoinduced and dark underpotential deposition of lead on selenium

The processes of the dark and photoinduced underpotential deposition (upd) of Pb ad-atoms on p-type Se electrodes have been studied. Under illumination with light absorbed by Se, the photoinduced upd of Pb ad-atoms (approximately a monolayer) onto the Se electrode occurs. The upd shift is about 800 mV. The Pb ad-atoms modify the Se surface and form electronic surface states in the Se bandgap, which promotes an efficient electron exchange between the valence band and redox species in solution. The surface states act as effective recombination centers for the photogenerated charge carriers and give rise to the subbandgap photocurrent enhancement. In the dark, the Pb upd occurs only on the electrode surface on which PbSe clusters were deposited. These clusters are formed both as a result of the chemical interaction of surface Se atoms with Pbbulk particles deposited at the cathodic polarization and due to the interaction of electrochemically generated H2Se with Pb2+ cations. The Pb ad-atoms deposited on the Se surface are electrochemically oxidized at more positive potentials (by ca. 150 mV) than those deposited on the surface of PbSe clusters.