Gold nanorods show great potential in harvesting natural sunlight and generating hot charge carriers that can be employed to produce electrical or chemical energies. We show that photochemical reduction of Pt(IV) to Pt metal mainly takes place at the ends of gold nanorods (AuNRs), suggesting photon-induced hot electrons are localized in a time-averaged manner at AuNR ends. To use these hot electrons efficiently, a novel synthetic method to selectively overgrow Pt at the ends of AuNRs has been developed. These Pt-end-capped AuNRs show relatively high activity for the production of hydrogen gas using artificial white light, natural sunlight, and more importantly, near IR light at 976 nm. Tuning of the surface plasmon resonance (SPR) wavelength of AuNRs changes the hydrogen gas production rate, indicating that SPR is involved in hot electron generation and photoreduction of hydrogen ions. This study shows that gold nanorods are excellent for converting low-energy photons into high-energy hot electrons, which can be used to drive chemical reactions at their surfaces.

We explored the use of salicylic acid (SA) and its derivatives 5-formylsalicylic acid (FSA) and 5-sulfosalicylic acid (SSA) as organic additives to cetyltrimethylammonium bromide (CTAB) in synthesizing gold nanorods (AuNRs) followed by palladium (Pd) capping at the ends of AuNRs. In the AuNR synthesis step, SA family additives in the presence of low concentration of CTAB (50 mM) serve as both the prereducing agent and the cofactor in nanorod growth. At an optimum additive/CTAB ratio (0.1–0.2), AuNRs grow to the longest length. At low additive concentrations, the gold seeds do not grow. At high concentrations, the longitudinal growth of AuNRs is disrupted because the excessive additive disturbs the ligand structure, leading to more isotropic growth. In the Pd overgrowth step, Pd starts to grow from both ends for AuNRs synthesized at optimum additive/CTAB ratios. Feeding more Pd grows the particles into a core–shell structure, possibly because there lacks a tight ligand layer on Pd that favors the longitudinal growth. For AuNRs synthesized at high additive/CTAB ratios, Pd growth loses preference, showing randomized Pd nucleation on AuNR surface. Finally, the palladium-end-capped–AuNRs’ catalytic activity was tested using the resazurin reduction reaction. This study shows a new way to produce controllable deposition of Pd on AuNRs.