Modification of large area Cu₂O/CuO photocathode with CuS non-noble catalyst for improved photocurrent and stability

In this work, a three-layered heterostructure Cu₂O/CuO/CuS was obtained through a low-cost and large-area fabrication route comprising electrodeposition, thermal oxidation, and reactive annealing in a sulfur atmosphere. Morphological, microstructural, and compositional analysis (AFM, SEM, XRD, EDS, XPS) were carried out to highlight the surface modification of cuprous oxide film after oxidation and subsequent sulfurization. Impedance, voltammetric, and amperometric photoelectrochemical tests were performed on Cu₂O, Cu₂O/CuO, and Cu₂O/CuO/CuS photocathodes in a sodium sulfate solution (pH 5), under 100 mW cm^-2 AM 1.5 G illumination. A progressive improvement in terms of photocurrent and stability was observed after oxidation and sulfurization treatments, reaching a maximum of - 1.38 mA cm^-2 at 0 V versus RHE for the CuS-modified Cu₂O/CuO electrode, corresponding to a ~ 30% improvement. The feasibility of the proposed method was demonstrated through the fabrication of a large area photoelectrode of 10 cm², showing no significant differences in characteristics if compared to a small area photoelectrode of 1 cm².