pH-driven tuning of n- to p-type conductivity transition and photocatalytic degradation of Methylene Blue in electrodeposited Cu₂O thin films

Abstract

Nanostructured Cu₂O thin films were electrodeposited under controlled pH conditions to investigate electrolyte pH effects on their structural, surface morphological, electrical, and photoelectrochemical properties. The study aimed to understand the pH-induced transition in conductivity type and to correlate it with microstructural evolution and photoelectrochemical and photocatalytic performance. Cyclic voltammetry was first performed to determine the optimal deposition potential, ensuring the selective formation of Cu₂O. The structural properties were analyzed by X-ray diffraction (XRD), confirming phase formation, crystallinity, and preferential orientation. Morphological investigations were carried out using scanning electron microscopy (SEM) and atomic force microscopy (AFM), revealing significant pH-dependent changes in grain size and surface roughness. Electrical properties were evaluated using Mott–Schottky analysis, demonstrating a clear transition from n-type to p-type conductivity with increasing pH. The photoelectrochemical behavior was further confirmed by photocurrent measurements, supporting the results obtained from electrochemical characterization. Finally, the optimized Cu₂O thin films were applied for the photocatalytic degradation of Methylene Blue under light irradiation, showing a moderate but well-defined, pseudo-first-order degradation of the dye under visible light. The results highlight the strong influence of pH on defect formation, carrier density, and overall performance, demonstrating that controlled electrodeposition is an effective strategy to tailor Cu₂O thin films for environmental applications, including photocatalytic pollutant degradation and photoelectrochemical energy conversion.