Effect of Substrates on the Photoelectrochemical Reduction of Water over Cathodically Electrodeposited p‑Type Cu₂O Thin Films

In this study, we demonstrate development of p-Cu₂O thin films through cathodic electrodeposition technique at constant current of 0.1 mA/cm² on Cu, Al, and indium tin oxide (ITO) substrates from basic CuSO₄ solution containing Triton X-100 as the surfactant at 30–35 °C. The optical and morphological characterizations of the semiconductors have been carried out using UV–vis spectroscopy, X-ray diffraction (XRD), scanning electron microscopy (SEM), and Raman spectroscopy. The band gap energy of ∼2.1 eV is recorded, whereas SEM reveals that the surface morphology is covered with Cu₂O semiconductors. XRD analyses confirm that with change in substrate, the size of Cu₂O “cubic” crystallites decreases from ITO to Al to Cu substrates. Photoelectrochemical characterizations under dark and illuminated conditions have been carried out through linear sweep voltammetry, chronoamperometry and electrochemical impedance spectroscopic analysis. The photoelectrochemical reduction of water (H₂O → H₂) in pH 4.9 aqueous solutions over the different substrates vary in the order of Cu > Al > ITO. The highest current of 4.6 mA/cm² has been recorded over the Cu substrate even at a low illumination of 35 mW/cm², which is significantly higher than the values (2.4 mA/cm² on Au coated FTO or 4.07 mA/cm² on Cu foil substrate at an illumination of 100 mW/cm²) reported in literature