Photoelectrochemical Properties of Annealed Anodic TiO2 Layers Covered with CuOx

In this work, we present a systematic study on the influence of Cu²⁺ ion concentration in the impregnation solution on the morphology, structure, optical, semiconducting, and photoelectrochemical properties of anodic CuO_x-TiO₂ materials. Studied materials were prepared by immersion in solutions with different concentrations of (CH₃COO)₂Cu and subjected to air-annealing at 400 °C, 500 °C, or 600 °C for 2 h. The complex characterization of all studied samples was performed using scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), reflectance measurements, Mott–Schottky analyses, and photocurrent measurements. It was found that band gap engineering based on coupling CuO with TiO₂ (E_g~3.3 eV) is an effective strategy to increase the absorption in visible light due to band gap narrowing (CuO_x-TiO₂ materials had E_g~2.4 eV). Although the photoactivity of CuO-TiO₂ materials decreased in the UV range due to the deposition of CuO on the TiO₂ surface, in the Vis range increased up to 600 nm at the same time.