Photoelectrochemical performance of graphene-modified TiO₂ photoanodes in the presence of glycerol as a hole scavenger

Graphene-modified TiO₂ (G-TiO₂) photoanode films were successfully prepared by a simple, versatile, and low-cost spray pyrolysis deposition method. The effects of graphene incorporation on the relevant properties of TiO₂ films were investigated by means of XRD, SEM, UV-vis absorbance spectroscopy, and photoelectrochemistry-related measurements. Bias-dependant efficiency calculated from linear-sweep voltammograms shows that the presence of graphene within the film networks, despite its low content, could promote a substantial improvement in maximum photoconversion efficiency from 0.39% (at-0.27 V vs HgO|Hg) to 0.65% (at-0.35 V vs HgO|Hg). This improvement is attributable to the enhancement of the electron-transferring ability upon the insertion of graphene, as confirmed by transient photocurrent analysis and Electrochemical Impedance Spectroscopy (EIS). The effectiveness of the photoelectrochemical cell employing G-TiO₂ as an excellent photoanode was further examined by running it in the presence of glycerol as a hole scavenger. Glycerol plays an important role as an effective sink for the photogenerated holes so that the surface charge recombination can be significantly suppressed and, subsequently, the photocurrent is enhanced. The additional photocurrent due to glycerol introduction into the cell depends upon the initial concentration of glycerol according to a model resembling a Langmuir-Hinshelwood isotherm. Based upon the results of the present study, further improvements in terms of graphene content, surface morphology modification or the use of other organic wastes as hole scavengers may be important for future investigation.