A photo-(electro)-catalytic system illustrating the effect of lithium ions on titania surface energetics and charge transfer

• Tuning the chemical role of electrons and holes controls surface and interface properties.
• Adsorption of Li+ in the dark causes a positive shift of the TiO2 bands.
• Due to Li+ adsorption/intercalation 4-nitrobenzaldehyde is selectively reduced.
• Li+ causes changes in the photo-electro oxidation mechanism of 2-propanol.

We describe the effect of Li+ on photoinduced charge transfer at TiO2 in acetonitrile solutions at open circuit (photocatalytic conditions) or under potential control. Using 2-propanol and 4-nitrobenzaldehyde as probe scavengers of holes and electrons, respectively, we aim to demonstrate the importance of tuning the chemical role of electrons and holes through control of surface and interface properties.Adsorption of Li+ in the dark causes a positive shift of the TiO2 bands as revealed by cyclic voltammetry and Mott–Schottky analysis. Likewise, there is clear evidence that dark adsorption of 2-propanol brings about a redistribution of the bandgap states.Electrochemical measurements show that, upon illumination, the charge of photo-accumulated electrons is compensated by Li+ that can undergo insertion at the surface/subsurface region, which prevents a negative shift of the bands and has important consequences on the overall photo(electro) catalytic processes. Concerning the fate of electrons, 4-nitrobenzaldehyde is selectively reduced to 4-aminobenzaldehyde probing that electron transfer specifically involves the NO2 moiety while reduction of the aldehyde functional group is observed only at much more negative potentials than Efb and is cation insensitive.Regarding the fate of photogenerated holes, the effect of Li+ is evident in the change of the mechanism of 2-propanol oxidation, as revealed by both electrochemical and EPR experiments. Adsorption as alcoholate occurs in the dark but it is strongly inhibited on pre-illuminated TiO2 in the presence of Li+.

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