Investigation of the photoelectrochemical properties for typical ZnO nanostructures grown by using chemical vapor transport

Typically, three kinds of ZnO nanostructures, nanowires, nanosheets, and nanorods, are synthesized by changing the reactor pressure in the chemical vapor transport method. The photoelectrochemical (PEC) properties of ZnO nanostructures were investigated by using an ultraviolet lamp with a wavelength of 365 nm and a measured intensity of 0.4 mW/cm²2. Photocurrent densities of 0.61, 0.47, and 0.37 mA/cm² were obtained for nanowires, nanosheets, and nanorods, respectively. The photoconversion efficiencies of these ZnO nanostructures under ultraviolet illumination were calculated as 73.1, 57.3, and 41.8%, respectively. The different PEC results were explained by using the effects of dimension in the nanostructures. The separation of light-induced charge formed near the surface, leading to the transfer of electron holes toward the surface and electrons toward the bulk at the photo-anode, will be higher as the dimension is decreased. The difference in the optical absorption in the PEC process could be neglected because the absorption intensities were nearly the same for the three kinds of samples, independent of both the morphology and the density. Therefore, the different PEC efficiencies could be thought to be a result of the difference in the nanostructures with different dimensions, not the result of the density of the nanostructure.