Charge-Transfer Dynamics in Nanorod Photocatalysts with Bimetallic Metal Tips

CdSe@CdS dot-in-rod nanostructures tipped with AuPt bimetallic nanoparticles as cocatalyst show increased photon-to-hydrogen conversion efficiency compared to their analogues with pure Au or Pt tips. The underlying charge separation and recombination processes are investigated by time-resolved transient absorption spectroscopy, to unravel whether the observed enhancement of photocatalytic activity is due to charge-separation/recombination properties of the system or to higher reactivity for proton reduction at the surface of the metal nanoparticle. We find that in the catalytically active Pt- and AuPt-functionalized structures charge separation occurs with similar time constants (Pt 3.5, 35, and 49 mu s AuPt 2.6, 31, and 66 ps), and the charge-separated state shows a lifetime of similar to 20 ys in both cases. Hence, these processes should not be regarded as a source of the increased catalytic efficiency in the AuPt-functionalized nanorods. The results indicate that the proton reduction at the metal nanoparticle surface itself determines the overall efficiency.