RESUMO
An ultra rapid growth method for vertically aligned ZnO nanorod (NR) thin films on metal meshes was developed using a direct heating synthesis technique. A typical NR growth rate of 10 µm h-1 was achieved. The effects of the applied heating power and growth duration on the morphologies of ZnO nanostructures were examined. High density surface defects were formed on the ZnO NRs, which is responsible for slow charge recombination and high efficiency in the photoelectrochemical (PEC) water splitting process. The light absorption for a photoanode was significantly improved by light trapping using a 3D stacked metal mesh photoanode structure. With the internal reflection between the stacked photoanodes, the final light leakage is minimised. The light absorption in the stacked photoanode is improved without restricting the charge transportation. In comparison with a single mesh photoanode and a chemical bath deposition grown flat photoanode, the PEC water splitting efficiency from the stacked photoanode was increased by a factor of 2.6 and 6.1 respectively.
RESUMO
Understanding the mechanism for growing TiO(2) nanotubes is important for controlling the nanostructures. The hydroxide nano-islands on the Ti surface play a significant role at the initial stage of anodization by forming the very first nano-pores at the interface between hydroxide islands and substrate and eliminating the H(2)O electrolysis. A quantitative time dependent SEM study has revealed a nanotube growth process with an initial linear increase of pore diameter, film thickness and number of pores. During the anodization of titanium, different current transient curves are observed for Ti samples with or without hydroxide on the surface. The transient current profile has been quantitatively analyzed by fitting several distinctive stages based on a growth mechanism supported by SEM observations. It is found that a saturated cubic dependent equation is appropriate to fit a short current upturn due to the increase of the surface area.