Morphological Modification of TiO₂ Thin Films as Highly Efficient Photoanodes for Photoelectrochemical Water Splitting

TiO2 films with modified morphology have been successfully synthesized via a facile spray-pyrolysis method in the presence of poly(ethylene glycol) (PEG) as a templating agent. The effects of the PEG concentration on the relevant properties of TiO2 films were investigated by means of scanning electron microscopy, X-ray diffraction, and UV-vis absorbance spectroscopy, while their photocatalytic properties were assessed by photoelectrochemical (PEC) water-splitting measurements. The introduction of 10 g·L(-1) PEG into the precursor solution leads to surface roughening with an exceptional improvement in PEC responses, revealing a photoconversion efficiency of 1.15% at -0.50 V vs HgO|Hg (in a 1 M NaOH electrolyte under broad-spectrum illumination), which is nearly triple that of the unmodified film (0.45% at -0.38 V vs HgO|Hg). Although the efficiency of the rough-surface photoanodes deteriorates upon increasing the PEG content, their PEC responses are still superior to those of smooth-surface films. Possible phenomena that might be responsible for the experimental observations are suggested and discussed accordingly.