Photocatalytic evolution of H2 over visible-light active LaMO3 (M: Co, Mn, Fe) perovskite materials: Roles of oxygenated species in catalytic performance

Abstract In this study, LaMO3 (M: Co, Mn, Fe) perovskite-based photocatalysts were synthesized using sol–gel and solid state methods. The activities of the perovskites as catalysts in the generation of H2 by water splitting were tested under simulated solar irradiation without sacrificial agents. The perovskites synthesized via the sol–gel route exhibited superior activities compared with those produced by the solid state reaction. The highest activity was obtained by LaMnO3 synthesized via the sol–gel route (103 μmol g−1 h−1) and the lowest by LaFeO3 produced in the solid state reaction (17 μmol g−1 h−1). The superior performance of LaMnO3 synthesized by the sol–gel route was attributed to its high surface area, smaller particle size, and the major currents detected by cyclic voltammetry related to the redox transitions of Mn+n ions exposed over the surface, which generated partial charges on the surface of the material, thereby increasing the active sites and the adsorption of water molecules to facilitate the reduction of H+/H2. Fourier transform-infrared and X-ray photoelectron spectroscopy analyses demonstrated that the lanthanum-based perovskites exhibited a high affinity for the adsorption of several oxygenated species, which reduced the catalytic activity due to the competition with water molecules. Pretreatment of the photocatalyst by degasification in a vacuum at 300 °C was tested as an efficient alternative for reducing the adsorption of these species. Our results demonstrated that pretreatment of the LaMnO3 perovskites increased their activity by up to 1.4 times.