Seed-Mediated Synthesis of NiPt-Alloy-Tipped CdSe/CdS Nanocrystals for Photocatalysis

We present a method for preparing NiPt-alloy tips on CdSe-core/CdS-shell dot-in-rod nanoparticles (DRs). The formation of the NiPt tips is separated into a two-step synthesis, where first Ni tips are grown, which then serve as nucleation sites for Pt before an alloying process occurs. Thus, the NiPt tips are formed in a seed-mediated approach. We find that the reactivity of the Ni tips can be controlled by oxygen treatment, while the reactivity of the lateral surface of the DRs can be tuned by ligands. Monitoring the growth dynamics of the NiPt reveals that an oxide layer on the Ni tips delays the nucleation of Pt, but it does not inevitably prevent it if a combination of oleic acid and oleylamine initiates oxide-layer conversion due to oleate formation. Without conversion, the oxide layer can be utilized to inhibit the NiPt formation. The choice of ligands can be exploited to enable or prevent separate Pt particle growth on the lateral semiconductor rod surface. Especially the DRs with NiPt-alloy tips show superior activity toward HER in both electrocatalytic and photocatalytic experiments.