Synthesis, Characterization of KNb0.99Eu0.01O3 and improved Photo-catalytic H2-Production on Ag/La2NiO4/ KNb0.99Eu0.01O3 hetero-junction

Abstract

The perovskite KNb_0.99Eu_0.01O₃ prepared by nitrate combustion is applied as a hydrogen photocathode in heterojunction with La₂NiO₄ under visible light. The XRD pattern confirms the formation of KNb_0.99Eu_0.01O₃ structure with orthorhombic single phase. The SEM images present grains between 0.2 and 0.4 µm while the optical band gap (3.14 eV) is calculated from the diffuse reflectance. Under illumination, the cyclic voltammetry (CV) and the capacitance measurements in Na₂SO₄ electrolyte show an increased current below ∼ -0.7 V vs. Ag/AgCl and p-type behavior with a conduction band (CB = −1.95 V) cathodically positioned with respect to H₂ level, thus leading to H₂ photo-production. The hetero-system La₂NiO₄/KNb_0.99Eu_0.01O₃ shows a much higher activity than KNb_0.99Eu_0.01O₃ where efficient H₂-photoevolution occurs with concomitant oxidation of S₂O₃²⁻, as reducing agent. So, the co-junction of La₂NiO₄ with KNb_0.99Eu_0.01O₃ facilitates the charge transfer and increases the reaction efficiency. At neutral pH, the H₂ evolution rate for the photocatalysts KNb_0.99Eu_0.01O₃ and La₂NiO₄/ KNb_0.99Eu_0.01O₃ are 11.15 and 57 µmol g⁻¹ min⁻¹; respectively. Further enhancement is observed with Ag-loaded La₂NiO₄/KNb_0.99Eu_0.01O₃, reaching a maximum hydrogen production rate of 67 µmol g⁻¹ min⁻¹, attributed to the lower overpotential introduced by Ag. These findings highlight the potential of the ternary system Ag/La₂NiO /KNb_0.99Eu_0.01O₃ as an efficient photocathode for H₂ generation.