Facile Sol-Gel-Derived Amorphous TiO2 Coating on Cu2O Photocathods for Photoelectrochemical Hydrogen Evolution

E. Mohammadi¹, D. Piccirilli¹, V. Ricci¹, V. Paolucci¹, C. Cantalini ¹

¹ Department of Industrial Engineering, University of L’Aquila, L’Aquila, Italy

ehsan.mohammadi@graduate.univaq.it

Cuprous oxide (Cu₂O) is a promising photocathode material for solar-driven hydrogen production because of its visible-light absorption, favorable band structure and elemental abundance¹. Nevertheless, its photoelectrochemical performance is limited by charge-carrier recombination, sluggish interfacial kinetics and susceptibility to photocorrosion². Here, electrodeposited Cu₂O films were coated with a sol–gel-derived amorphous TiO₂ (a-TiO₂) overlayer to investigate its influence on photoelectrochemical water-reduction performance.

Cu₂O was electrodeposited on fluorine-doped tin oxide substrates at ambient temperature, followed by spin coating of a TiO₂ precursor and mild thermal treatment at 80 °C. X-ray diffraction confirmed the formation of crystalline Cu₂O, while no detectable reflections attributable to crystalline TiO₂ were observed, consistent with the formation of a thin amorphous overlayer. Electron microscopy revealed homogeneous surface coverage following a-TiO₂ deposition. Diffuse-reflectance spectroscopy showed increased visible-light absorption intensity for Cu₂O/a-TiO₂ compared with bare Cu₂O. Tauc analysis yielded apparent optical band gaps of 3.30, 2.16 and 2.34 eV for a-TiO₂, Cu₂O and Cu₂O/a-TiO₂, respectively.

Photoelectrochemical measurements under dark and simulated-solar illumination demonstrated a clear cathodic photoresponse from both electrodes. Compared with bare Cu₂O, the Cu₂O/a-TiO₂ heterostructure exhibited an enhanced and reproducible photocurrent, with an approximately twofold increase under simulated sunlight, by obtaining -0.3 mA/cm². Measurements under red, green, purple-blue and simulated-solar illumination confirmed the wavelength-dependent photoactivity of the heterostructure across the visible region. Chopped-light chronoamperometry at 0 V versus RHE exhibited rapid and repeatable light–dark switching. Furthermore, a-TiO₂ deposition substantially suppressed the transient photocurrent spikes observed under chopped monochromatic illumination. Electrochemical impedance spectroscopy indicated a lower interfacial charge-transfer resistance for Cu₂O/a-TiO₂, supporting improved charge-transfer kinetics at the photocathode–electrolyte interface.

These results demonstrate that facile, low-temperature sol–gel processing provides a viable and accessible route for integrating amorphous TiO₂ coatings with Cu₂O photocathodes and improving their photoelectrochemical interfacial performance.