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The Effect of Ascorbic Acid as a Hole Scavenger on Electrochemical Responses of Photocatalysts

Photoexcitation of the semiconductor yields electron-hole pairs that rapidly recombine. However, this recombination can be prevented by the addition of hole scavengers which increases the survival probability of the electrons. Different organic hole scavengers have been employed to elucidate reaction mechanisms or to improve the reaction efficiency in heterogeneous photocatalysis and electrochemical photocatalysis (PEC) for more than 50 years. Nevertheless, their influence on the electrochemical response of photocatalysts has yet to be thoroughly researched. This work is focused on the study of ascorbic acid (AA) as a scavenger for photogenerated holes and its effect on the electrochemical response of photocatalysts. Considering that the formal potential of the AA redox couple is – 0.185 V (vs SCE) it can be easily oxidized by the photogenerated holes. For the purpose of this investigation photoelectrochemical characterization of TiO2 and TiO2/SnO2 electrodes was carried out in the presence of AA. The electrodes were prepared by the deposition of a commercial TiO2 and laboratory prepared TiO2/SnS2 onto FTO glass plates. All measurements were done in a phosphate buffer solution with or without the addition of AA and by using a three electrode system. Irradiation was carried out by UV or LED lamps. Open circuit potential (OCP) monitoring in chopped light irradiation indicated an increase in photocatalytic activity in the presence of AA. Moreover, linear sweep voltammetry (LSV) and electrochemical impedance spectroscopy (EIS) responses showed that by the addition of AA higher photocurrents and lower resistances, respectively, are obtained.

hole scavengers ; electrochemical photocatalysis ; ascorbic acid ; TiO2 ; TiO2/SnS2

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