Anodized ZnO nanostructures for photoelectrochemical water splitting

•ZnO nanostructures were synthesized by electrochemical anodic process.•The parameter of ZnO nanostructure was anodic potential.•The model of growth of ZnO nanostructure was investigated. Zinc oxide (ZnO) nanostructures were fabricated on the polished zinc foil by anodic deposition in an alkaline solution containing 1.0M NaOH and 0.25M Zn(NO3)2. Potentiostatic anodization was conducted at two potentials (−0.7V in the passive region and −1.0V in the active region vs. SCE) which are higher than the open circuit potential (−1.03V vs. SCE) and as-obtained ZnO nanostrcutures were investigated focusing on their structural, optical, electrical and photoelectrochemical (PEC) characteristics. All samples were confirmed ZnO by X-ray photoelectron spectroscopy and Raman spectra. Observations in the SEM images clearly showed that ZnO nanostructures prepared at −0.7V vs. SCE were composed of nanowires at while those obtained at −1.0V vs. SCE possessed nanosheets morphology. Result from transmission electron microscope and X-ray diffraction patterns suggested that the ZnO nanowires belonged to single crystalline with a preferred orientation of (002) whereas the ZnO nanosheets were polycrystalline. Following PEC experiments indicated that ZnO nanowires had higher photocurrent density of 0.32mA/cm2 at 0.5V vs. SCE under 100mW/cm2 illumination. This value was about 1.9 times higher than that of ZnO nanosheets. Observed higher photocurrent was likely due to the single crystalline, preferred (002) orientation, higher carrier concentration and lower charge transfer resistance.