Nanostructured ZnO, CuO, and CuO/ZnO composites: a comparative study of their photoelectrochemical performance

Abstract

In this study, a CuO/ZnO nanocomposite photoelectrode was effectively synthesized via a two-step process involving the hydrothermal growth of ZnO nanorods (ZNRs) followed by electrochemical cathodization for CuO nanoparticle deposition. The integration of CuO and ZnO influenced the complementary properties of both materials: CuO, with its narrow band gap, acted as a highly responsive visible-light absorber, while ZnO exhibited high electron mobility for efficient charge transport. XRD analysis confirmed the wurtzite crystal structure of ZnO and the monoclinic phase of CuO. FESEM images revealed vertically aligned ZnO nanorods with enhanced surface coverage after CuO deposition, while EDX confirmed the elemental composition of Zn, O, and Cu in the composite. Furthermore, UV-vis spectra exhibited a noticeable red shift with a band gap reduction from 3.26 eV (ZnO) to 1.65 eV (CuO/ZnO), thereby improving visible light absorption. This heterojunction structure could promote effective charge separation and enhance photoelectrochemical (PEC) performance. The successful construction of the CuO/ZnO composite was verified by structural and morphological analyses. Photoelectrochemical measurements revealed a remarkable enhancement in the photocurrent response, where the ZnO nanorod electrode coated with a CuO layer deposited for 2 minutes (CuO-2 min/ZnO) exhibited the highest PEC performance, delivering an anodic photocurrent density of 2.05 mA cm⁻² at 1.0 V vs. Ag/AgCl, compared to 0.116 mA cm⁻² for bare ZnO nanorods. This substantial improvement confirms the effectiveness of the construction method and highlights the potential of CuO/ZnO nanocomposites as efficient photoelectrodes for solar-driven applications such as water splitting (e.g., for hydrogen production) and environmental remediation.