The photoelectrochem. properties of ZnO electrodes were studied in the near-UV region. Studies were carried out on electrodes with different morphologies, porosities, and film thicknesses to probe the influence of these parameters on the photoelectrochem. characteristics. The highest incident photon-to-current conversion efficiencies of 90 and 30% for illumination through the conducting substrate and directly on the ZnO, resp., were obtained with a 8 μm thick ZnO film consisting of 150 nm spherical particles. For this system, no significant decrease in the photocurrent due to addn. of iodine or oxygen to the electrolyte was found. The electron losses from the conduction band of the ZnO electrodes are restricted to the zone of charge-carrier generation.