Photocatalytic generation of hydrogen under visible light on La₂CuO₄

Abstract

The semiconducting properties of La₂CuO₄ prepared by a chemical route are investigated for the first time by the photo-electrochemical technique. The optical gap is found to be 1.27 eV and the transition is directly allowed. p-Type conductivity is demonstrated from the Mott–Schottky plot in alkaline KOH solution (0.1 M), extrapolation of the linear region to the potential axis gives a flat band potential of −0.41 V_SCE, a holes density of 1.75 × 10¹⁹ cm⁻³ and a space-charge region of 18 nm. The electrochemical impedance spectroscopy, measured over the frequency range (1 mHz–10⁵ Hz), reveals the predominance of the bulk contribution with a constant phase element. The energy diagram shows the feasibility of La₂CuO₄ for the H₂ evolution under visible light. The best performance occurs at pH 12.5 in the presence of S$_{\mathbf {2}}\textit {O}_{\mathbf {3}}^{\mathbf {2-}}$ as holes scavenger. A liberation rate of 20.6 μmol mn⁻¹ (g catalyst)⁻¹ is obtained under full light (29 mW cm⁻²).