Preparation, characterization and electronic properties of LaFeO3 perovskite as photocatalyst for hydrogen production

Abstract

Perovskite-type LaFeO3 was successfully used as photocatalyst for the H2 production. It was prepared by a conventional sol-gel technique via the nitrate route. X-Ray fluorescence/Energy Dispersive X-Ray fluorescence (XRF), X-Ray Diffraction (XRD), X-Ray photoelectron spectroscopy (XPS), UV–Visible diffuse reflectance, FTIR spectroscopy, Scanning Electron Microscopy (SEM/EDX) and specific surface area were deployed to characterize the synthetized material after heat-treated at 850 °C. LaFeO3 crystallizes in a cubic structure (Space Group: Pm3 m) with a crystallite size of 16 nm and BET surface area of 12 m2/g. Field-dependent magnetization was measured at 300 K in the region (±25 kOe) and the perovskite exhibits a high magnetism with a saturation magnetization (0.15 emu/g). Such result indicates that the Fe-3d are in localized high spin state. LaFeO3 has a narrow band gap of 2.08 eV determined by diffuse reflectance resulting to the crystal field splitting of 3d orbital of Fe3+ octahedrally coordinated with an internal d-d transition. Cyclic voltammetry showed the reduction of adsorbed H2O molecules to gaseous hydrogen at −0.7 VSCE, a potential less cathodic than the conduction band (−0.45 VSCE). The latter was determined from the capacitance measurements in alkaline electrolyte (NaOH 0.1 M) where the perovskite exhibits a stability with an exchange current density of ∼0.4 mA cm−2. The photocatalytic activity reveals an optimal H2 production of 99 μmol after 20 min at 50 °C in NaOH medium and a catalyst mass of 50 mg, under visible light irradiation (13 W) in the presence of thiosulfate S2O32− as hole scavenger.