The effect of nanostructure dimensionality on the photoelectrochemical properties of derived TiO₂ films

Studying the effect of nanoscale morphology on the photoelectrochemical performance of semiconductor electrodes has been in the forefront of research for over a decade, there are still major inconsistencies and controversies in the literature. Here we aimed to resolve some of these issues, by the controlled preparation of TiO₂ photoelectrodes from nanoparticles, nanorods, and nanosheets, where the nano dimension of the 0D, 1D, and 2D structures was kept similar (about 10 nm). XRD, Raman spectroscopy, XPS and UPS were employed to confirm that the chemical nature of the nanostructures is nearly identical, they only differ in their morphology. Photoelectrodes were prepared keeping the loading amount, surface area, or the film thickness identical, to deconvolute all trivial effects, and only scrutinize the role of morphology. TiO₂ nanorod (NR) films exhibited the best photoelectrochemical performance in all comparisons, achieving ~4 mA cm⁻² at 0.2 V vs. Ag/AgCl (under 100 mW cm⁻², Xe-lamp illumination). In stark contrast, TiO₂ nanosheet (NS) film showed the lowest performance owing to the small amount of active sites on the basal plane of the NSs and the insufficient charge carrier transport through the film. Overall, we have demonstrated that under carefully controlled conditions, it is possible to compare the PEC behavior of TiO₂ photoelectrodes, and that the 1D nanostructures outperformed its 0D and 2D counterparts.