Inhibition of hydrogen and oxygen reverse recombination reaction over Pt/TiO2 by F− ions and its impact on the photocatalytic hydrogen formation

Abstract

Photoelectrochemical and photocatalytic water splitting to generate hydrogen are regarded as potential methods to obtain hydrogen. In the semiconductor photocatalytic dispersion, noble metallic Pt is usually used as a co-catalyst to catalyze those reactions. However, Pt can also act as an active center for H2 and O2 recombination back reaction, which results in the very low photocatalytic efficiency for H2 generation. Here we reported that the recombination rate nearly linearly increased with the increase of Pt loading amount in the low Pt loading region, while decreased in high Pt loading region. Very trace amount of fluorine ion can remarkably inhibit hydrogen and oxygen recombination. Detail study indicated that this inhibition was achieved via the occupation of hydrogen and oxygen adsorption and activation sites by fluorine ion over Pt due to the strong tendency of adsorption of fluorine ion on Pt. By taking advantage of this inhibition role of fluorine ions, the Pt/TiO2 activity for water splitting is remarkable enhanced up to 2.3 times. Isotope experiments with D2O and H218O confirmed hydrogen and oxygen were both from water. Our results clearly indicated that the excellent photocatalytic performance for water splitting over fluorine doped on TiO2 might be related to the role of fluorine inhibition on H2 and O2 recombination back reaction, which would shine light to the new photocatalyst preparation for water splitting.