Elaboration and studies of physical and photo-electrochemical properties of La2NiO4 and its use with SnO2 in photo-evolution of hydrogen under visible light irradiation

Abstract

La2NiO4 elaborated by nitrate route gives a positive result when used as a catalyst for the hydrogen photo-evolution. The prepared oxide crystallizes in the tetragonal K2NiF4 structure I4/mmm. The BET method was used to determine the specific surface area (4.91 m2/g); such value could suggest an interesting catalytic activity. Optical, electrical and photo-electrochemical properties have been studied to elaborate the energy diagram, a preamble for the photocatalysis. The band gap (Eg) has been evaluated at 1.51 eV and the transition is directly allowed. La2NiO4 is p-type semiconductor assigned to O2− intercalation in the two-dimensional crystal lattice; activation energy of 0.13 eV in the heating direction from the Arrhenius type law. The flat band potential Efb (−0.45 VSCE) and the density of the holes NA (1.13 × 1021 cm-3) were computed from the capacitance measurement. The conduction band illustrated in the energetic diagram for La2NiO4 (−1.77 VSCE) offers the possibility of H2 generation upon visible light. The best performance occurs at pH 13 in the presence of S2O3-3 as a hole scavenger. The H2 generation of the hetero-system (La2NiO4/SnO2) is significantly improved compared to La2NiO4. The higher photoactivity is ascribed to the electrons injection from the conduction band (La2NiO4-CB = −1.77 V/SCE), acting as generator and electrons pump, to (SnO2-CB = 0.35 V/SCE) inducing a better water reduction. The H2 evolution rate reaches 15.1 μmol g−1 min−1.