Abstract The photoelectrochemical behavior of a number of photoelectrodes prepared in polycrystalline form from 99.9% iron (Armco) under controlled thermal oxidation conditions is reported. The steady-state polarization curves show a complicated aspect corresponding to changes in the charge transfer kinetics. A strong influence of the surface oxide thickness ( d) on both the electrochemical characteristics and the photocurrent efficiency is found. Maximum photocurrents are measured on oxide covered electrodes with d < 10 4 Å. The long term stability of the electrodes covered with oxide layers of thickness less than 10 3 Å is unsatisfactory.