Enhanced photoelectrocatalytic hydrogen evolution using off-stoichiometry La0.43FeOy films

Abstract In this work, the influence of the stoichiometry of LaxFeOy films on their activity for H2 production by photoelectrochemical (PEC) water splitting was investigated. Thin LaxFeOy films were deposited on electrodes by magnetron co-sputtering and their composition was controlled by adjusting the power applied on metallic iron and lanthanum targets. The highest photoactivity was observed for La0.43FeOy films. The crystallization of these films and their photocatalytic activity were further improved by oxidation in an external furnace at 650°C for 2 h. Transmission electron microscopy (TEM) analyses confirm the formation of LaFeO3 crystallites in the film and show a thin continuous polycrystalline Fe2O3 layer at the surface. The presence of Fe2O3 at the upper surface originates from an exsolution mechanism typically observed for non-stoichiometric perovskites. The improvement of the photocatalytic properties by adjusting the stoichiometry, the oxidation temperature and the film thickness was confirmed by H2 production measurements performed by mass spectrometry. We observe a large increase in H2 production rate (103%) by comparison with a stoichiometric LaFeO3 thin film. The improvement in catalytic performances for these non-stoichiometric films composed of earth abundant, low-cost and non-toxic elements, make them of high interest materials for photoelectrodes in PEC water splitting systems.