Efficient Plasmon-Mediated Energy Funneling to the Surface of Au@Pt Core–Shell Nanocrystals

Abstract

The structure and ultrafast photodynamics of ~8 nm Au@Pt core-shell nanocrystals with ultrathin (<3 atomic layers) Pt-Au alloy shells are investigated to show that they meet the design principles for efficient bimetallic plasmonic photocatalysis. Photoelectron spectra recorded at two different photon energies are used to determine the radial concentration profile of the Pt-Au shell and the electron density near the Fermi energy, which play a key role in plasmon damping and electronic and thermal conductivity. Transient absorption measurements track the flow of energy from the plasmonic core to the electronic manifold of the Pt shell and back to the lattice of the core in the form of heat. We show that strong coupling to the high density of Pt(d) electrons at the Fermi level leads to accelerated dephasing of the Au plasmon on the femtosecond timescale, electron-electron energy transfer from Au(sp) core electrons to Pt(d) shell electrons on sub-picosecond timescale, and enhanced thermal resistance on the 50 ps timescale. Electron-electron scattering efficiently funnels hot carriers into the ultrathin catalytically active shell at the nanocrystal surface, making them available to drive chemical reactions before losing energy to the lattice via electron-phonon scattering on the 2 ps timescale. The combination of strong broadband light absorption, enhanced electromagnetic fields at the catalytic metal sites, and efficient delivery of hot carriers to the catalyst surface make core-shell nanocrystals with plasmonic metal cores and ultrathin catalytic metal shells promising nanostructures for the realization of high-efficiency plasmonic catalysts.

Fine‐Tuning Au@Pd Nanocrystals for Maximum Plasmon‐Enhanced Catalysis

“…In all these core particles with various sizes and shapes, the highest reaction rate was always achieved for the thinnest Pd coating, which correlates well with the highest plasmonic enhancement as shown in the thinnest Pd coating (Figure S11, Supporting Information). Our observation is in excellent agreement with literature, [ 31 ] supporting the argument on maximum plasmon‐adsorbate coupling, highest density/energy of hot electrons/carriers for ultrathin shell coating. Since only surface‐bonded Pd atoms played a major role in catalytic reaction, it makes sense that the thinnest Pd coating represented the most economic use of relatively more expensive Pd elements.…”

“…[ 29,30 ] The progressive broadening LSPR profiles with addition of Pd demonstrates the strong electronic coupling between Au LSPR and catalytic Pd at the surfaces. [ 31 ] In spite of Pd‐induced damping, the core–shell nanocrystals remain strong LSPR profiles which are important for plasmonic photocatalysis.…”

“…The apparent higher activity energy demonstrated the additional photochemical effects, in which hot‐electrons generated from Au core can efficiently transfer into Pd shells and funnel onto nanocrystal surfaces to lower energy barriers for chemical reactions. [ 9,31 ]…”

Plasmonic Au–Pd Bimetallic Nanocatalysts for Hot-Carrier-Enhanced Photocatalytic and Electrochemical Ethanol Oxidation

“…CV scans in the dark and under AM1.5G irradiation are shown in Supplementary Figures S10-S12. Catalytic metals like Pt and Pd enhance the extraction and use of plasmonic carriers generated in Au [4,18,20,28,29,43,53,54]. Furthermore, hot electron transfer and photothermal processes can facilitate intermediate removal during irradiation [3,5,9].…”

Sharp Spectral Variations of the Ultrafast Transient Light Extinction by Bimetallic Nanoparticles in the Near‐UV

“…Let us underline that this simplification could not have been possible with other metal combinations, such as Au and Pt. [31][32][33] In this way, the time evolution of both T e and T l inside the NPs have been determined. These values have been used to calculate the transient variation of the dielectric functions of Au and Ag following the method already used previously for Au.…”