Sensitization of Pt/TiO₂ Using Plasmonic Au Nanoparticles for Hydrogen Evolution under Visible-Light Irradiation

Au nanoparticles with different sizes (10, 20, 30, and 50 nm) were synthesized using a seed-assisted approach and anchored onto Pt/TiO 2 employing 3-mercaptopropionic acid as the organic linker. The sizes of the Au nanoparticles were controlled within a narrow range so that the size-dependent surface plasmonic resonance effect on sensitizing Pt/TiO 2 can be thoroughly studied. We found that 20 nm Au nanoparticles (Au 20 ) gave the best performance in sensitizing Pt/TiO 2 to generate H 2 under visible-light illumination. Photoelectrochemical measurements indicated that Au 20 -Pt/TiO 2 exhibited the most efficient “hot” electrons separation among the studied catalysts, correlating well with the photocatalytic activity. The superior performance of Au-supported Pt/TiO 2 (Au 20 -Pt/TiO 2 ) compared with Au anchored to TiO 2 (Au 20 /TiO 2 ) revealed the important role of Pt as a cocatalyst for proton reduction. To elucidate how the visible-light excited hot electrons in Au nanoparticles involved in the proton-reduction reaction process, Au 20 /TiO 2 was irradiated by visible light (λ > 420 nm) with the presence of Pt precursor (H 2 PtCl 6 ) in a methanol aqueous solution under deaerated condition. Energy-dispersive X-ray spectroscopy mapping analysis on the recovered sample showed that Pt ions could be reduced on the surfaces of both Au nanoparticles and TiO 2 support. This observation indicated that the generated hot electrons on Au nanoparticles were injected into the TiO 2 conduction band, which were then subsequently transferred to Pt nanoparticles where proton reduction proceeded. Besides, the excited hot electrons could also participate in the proton reduction on Au nanoparticles surface.