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Ascorbic Acid Influence on the Photoelectrochemical Response of TiO2 and SnS2

TiO2 is already a well-studied photocatalytic material because of its excellent properties such as chemical stability, low price, non-toxicity. However, the fact that its band gap (3, 2 eV) allows it to absorb only the UV light limits its use. On the other hand, SnS2 (band gap ~2, 2 eV) absorption range is well within the visible light spectrum which is more suitable for solar harvesting. Both of these materials are semiconductors which yield rapidly recombining electron-hole pairs upon photoexcitation. This recombination can be prevented by the addition of hole scavengers, which increase the survival probability of the electrons. Over the years there have been various efforts to improve such reaction efficiency using different organic hole scavengers. This work was focused on the influence of ascorbic acid (AA) as a scavenger for photogenerated holes and its influence on the photoelectrochemical response of TiO2 and SnS2. Since the formal potential of the AA redox couple is 0.5 V (vs SCE) it means it can be easily oxidized by the photogenerated holes. The aim of this investigation was to compare the electrochemical responses of different photocatalytic materials (TiO2 and SnS2 electrodes) in the presence and absence of ascorbic acid. Using the techniques of linear sweep voltammetry (LSV) and electrochemical impedance spectroscopy (EIS) it was found that the addition of ascorbic acid increases the photocurrents and lowers the resistances. Open circuit potential (OCP) monitoring in chopped light irradiation suggested an increase in photocatalytic activity in the presence of AA. The obtained results indicate that ascorbic acid can be used as an efficient hole scavenger.

TiO2, SnS2, recombination, ascorbic acid

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