Hydrothermal fabrication and photocatalytic study of delafossite (CuFeO2) thin films on fluorine-doped tin oxide substrates

Highlights: • Hydrothermal fabrication of CuFeO₂ thin films on FTO substrates through CuFeO₂-powder-based seed layers. • Amounts of defective Cu²⁺_Cu+ (approximately 29%) and V_O²⁺ (approximately 9%) after hydrothermal reactions. • Energy band diagram of CuFeO₂ films supporting their applications in photodegradation and PEC water splitting. • 20-seed-layer-based samples exhibiting the highest photodecomposition of MB and RhB solutions and a reliable photocurrent. • Synergistic effect of excellent crystallinity, low PL emission signals, and high electrochemical surface areas. Delafossite (CuFeO₂) thin films were hydrothermally synthesized on fluorine-doped tin oxide substrates by using CuFeO₂-powder-based seed layers; the photocatalytic properties of these thin films were then investigated. Annealing at 300 °C before hydrothermal reactions yielded thermodynamically stable CuFeO₂ islands, which were crucial for strong adhesion of hydrothermal CuFeO₂ films. Pure hydrothermal CuFeO₂ films were obtained when more than 10 seed layers were used. The proportions of defective Cu²⁺_Cu+ and V_O²⁺ decreased greatly to approximately 29% and 9%, respectively, after hydrothermal reactions, indicating that the fabricated films were predominantly CuFeO₂. The energy band diagram of the CuFeO₂ films supported their potential for application in photodegradation and photoelectrochemical water splitting. Samples fabricated using 20 seed layers exhibited the highest photodecomposition of methylene blue and Rhodamine B solutions under visible light irradiation. The maximum applied bias photon-to-current conversion efficiency was observed at a bias of −0.5 V, and a cycling study revealed a reliable photocurrent. These photocatalytic properties were attributable to excellent crystallinity, low photoluminescence emission signals, and high electrochemical surface area, all of which contributed to the smooth transport of photoinduced electron−hole pairs to the sample surfaces, thus effectively inducing photocatalysis.