Effects of Bi-dopant and co-catalysts upon hole surface trapping on La2Ti2O7 nanosheet photocatalysts in overall solar water splitting

Pristine and Bi-doped lanthanum titanium oxide (La2Ti2O7) nanosheets have been synthesized as photocatalysts for overall solar water splitting. The surface hole trap is a critical factor that limits the photocatalytic activity of pristine La2Ti2O7. Deposition of cobalt phosphate (Co-Pi) and platinum (Pt) nanoparticles on La2Ti2O7 cannot remove the surface traps although they are essential for enabling the oxygen and hydrogen evolution reactions. It is interesting that doping bismuth (Bi) into La2Ti2O7 nanosheets has eliminated the surface traps due to surface enrichment of Bi. The Co-Pi/Bi-La2Ti2O7/Pt nanosheets exhibit increasing photocatalytic activity toward overall water splitting with increasing the Bi-dopant level up to 5 at.%. Further increasing the Bi-dopant level leads to the formation of localized states above the valence band, leading to the lifetime reduction of photogenerated charge-carriers, and jeopardizing the photocatalytic activity. This work proposes an effective strategy to address the surface trapping and surface catalysis issues in the nanostructured metal oxide photocatalysts.