An epitaxial La₂CuO₄ thin film photocathode for water splitting under visible light

A semiconductive oxide, La₂CuO₄ (LCO), was investigated as a potential material to compose photocathode for sunlight-driven hydrogen evolution by splitting water. LCO, despite involving partially filled Cu 3d orbitals, behaves as a semiconductor and absorbs visible light on the bandgap formed by significant Coulomb repulsion between the electronic orbitals. An epitaxial LCO film was grown on a SrRuO₃/SrTiO₃ (SRO/STO) single-crystal substrate by pulsed laser deposition to obtain a photocathodic specimen for water photo-splitting. An LCO photocathode dressed with a Pt cocatalyst for hydrogen evolution (Pt/LCO/SRO/STO) exhibited a cathodic photocurrent with a density of 0.4 mA cm⁻² at 0 V_RHE under simulated AM1.5 G sunlight. This photocathode responded to incident light up to 800 nm, which is one of the longest wavelengths so far reported for an oxide photoelectrode. Together with a counter-electrode for oxygen evolution, the Pt/LCO/SRO/STO photocathode generated hydrogen with the expected H₂ : O₂ = 2 : 1 stoichiometric ratio with a Faradaic efficiency of approximately 80%.