Effect of electrodeposition temperature on the thin films of ZnO nanoparticles used for photocathodic protection of SS304

Films of ZnO nanoparticles were electrodeposited on indium-doped tin oxide (ITO) glass under different temperatures between 40 and 80 °C to study their photogenerated cathodic protection to stainless steel 304 (SS304). Morphology, crystallographic information and optical performance of the ZnO films were studied by scanning electron microscopy (SEM), X-ray diffraction (XRD), UV–vis spectroscopy and photoluminescence (PL) spectroscopy, respectively. The photocathodic protection of ZnO films on SS304 were evaluated by electrochemical methods. It was found that the ZnO films obtained at 40 °C is cauliflower-like in microstructure, while those obtained between 60 and 80 °C are hexagonal nanorods. The films prepared at 40 °C cause the most negative shift of the open circuit potential (OCP) of SS304 and produce photocurrent more than 10 times greater than those of the films obtained at higher temperatures. The excellent photocathodic performance of the ZnO nanoparticles prepared at 40 °C is attributed to the abundance of defects in its microstructure, which greatly reduces the electron-hole recombination rate upon UV illumination. The findings in this paper reveal that the defective ZnO nanoparticles obtained at low electrodeposition temperature display more efficient photocathodic protection and controlling the defects in semiconductor material may be a feasible way to improve its photoactivity.