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. To investigate 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, the function immanent charge-separation and recombination processes are investigated by time-resolved transient absorption spectroscopy. 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 ps; AuPt 2.6, 31, and 66 ps) and the charge-separated state shows a lifetime of ~20 μs in both cases. Hence, these processes should not be regarded as 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.