Morphology-Tuned TiO2 Photoelectrodes and Their Charge Transfer Behaviour: From 0- to 2-Dimensional Nanostructure

Abstract

Anatase TiO2 photoelectrodes, consist of the different nanoparticle (sphere, sheet, rod) were synthesized using hydrothermal and spray coating method. The surface characterizations of TiO2 films were demonstrated by various analysis tool (TEM, XPS, XRD, DRS), and their photoelectrochemical activities were evaluated by controlling the film parameters (mass loading, surface area, thickness) under sulfite and sulfate solution. The particle size and oxidation state of Ti is nearly identical despite of shape difference; however, the band position estimation from the optical bandgap and valence band maximum (VBM) expects that TiO2 nanorod (TiO2 NR) leads to facilitate the separation of photogenerated electron-hole pair due to the lowest VBM position and narrow bandgap (Eg = 3.22 eV). TiO2 NR film exhibits superiority in the photocurrent generation, achieving ~4 mA cm-2 at 0.2 V vs. Ag/AgCl in all film parameter conditions. The IPCE of TiO2 NR achieved the highest values at 350 nm, and high APCE values indicate that restricted the charge recombination or charge carrier trapping on the surface. The fast charge transfer leads to the improvement of the photoelectrochemical performance of TiO2 NR film, which is demonstrated by Intensity-modulated photocurrent spectroscopy (IMPS) and charge injection efficiency. This study provides a significant insight between the morphology change and the charge transfer phenomena on the surface.