Nanostructured ZnO, CuO, and CuO/ZnO Composites: A Comparative Study of Photoelectrochemical Performance

Abstract

In this study, a CuO/ZnO nanocomposite photoelectrode was effectively synthesized via a two-step process including the hydrothermal growth of ZnO nanorods (ZNRs) trailed by electrochemical cathodization for CuO nanoparticle deposition. The considered integration of CuO and ZnO influences the complementary properties of both materials, CuO, with its narrow band gap, performances as a highly responsive visible-light absorber, while ZnO proposals 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 is predictable to 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/cm² at 1.0 V vs. Ag/AgCl, compared to 0.116 mA/cm² 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 and environmental remediation, such as hydrogen production through water splitting.