Single step fabrication of CuO–MnO–2TiO2 composite thin films with improved photoelectrochemical response

Abstract

Novel trimetallic composite oxide CuO–MnO–2TiO₂ thin films have been deposited on glass substrates, which were coated with fluorine-doped tin oxide (FTO), by aerosol-assisted chemical vapor deposition (AACVD) using a 1 : 1 : 2 non aqueous mixture of copper(II) acetate monohydrate (Cu(CH₃COO)₂·H₂O), anhydrous manganese(II) acetate (Mn(CH₃COO)₂) and titanium(IV) butoxide (Ti(O(CH₂)₃CH₃)₄) in the presence of trifluoroacetic acid (TFA). Thin films were characterized by Fourier transform infrared spectroscopy (FT-IR), Raman, X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), energy dispersive spectroscopy (EDX) and X-ray photoelectron spectroscopy (XPS), suggesting the formation of a crystalline mixture of CuO–MnO–2TiO₂ composite with well defined and evenly distributed particles. The direct band gap energy of 1.95 eV was estimated by UV-Vis spectroscopy. From its current–voltage characterization, it is evident that the nanostructured CuO–MnO–2TiO₂ photoelectrode deposited at 550 °C for 45 minutes displayed enhanced photocatalytic activity in photoelectrochemical (PEC) water splitting and yielded a photocurrent of 2.21 mA cm⁻² at +0.7 V vs. Ag/AgCl/3 M KCl using a 0.5 M Na₂SO₄ electrolyte under AM 1.5 G illumination (100 mW cm⁻²). The charge transfer dynamics of the thin film were also explored using an electrochemical impedance spectroscopy (EIS) technique.