Single-Particle Insights into Plasmonic Hot Carrier Separation Augmenting Photoelectrochemical Ethanol Oxidation with Photocatalytically Synthesized Pd–Au Bimetallic Nanorods

Abstract

Understanding the nature of hot carrier pathways following surface plasmon excitation of heterometallic nanostructures and their mechanistic prevalence during photoelectrochemical oxidation of complex hydrocarbons, such as ethanol, remains challenging. This work studies the fate of carriers from Au nanorods before and after the presence of reductively photodeposited Pd at the single-particle level using scattering and emission spectroscopy, along with ensemble photoelectrochemical methods. A sub-2 nm epitaxial Pd0 shell was reductively grown onto colloidal Au nanorods via hot carriers generated from surface plasmon resonance excitation in the presence of [PdCl4]2–. These bimetallic Pd–Au nanorod architectures exhibited 14% quenched emission quantum yields and 9% augmented plasmon damping determined from their scattering spectra compared to the bare Au nanorods, consistent with injection/separation of intraband hot carriers into the Pd. Absorbed photon-to-current efficiency in photoelectrochemical ethanol oxidation was enhanced 50× from 0.00034% to 0.017% due to the photodeposited Pd. Photocurrent during ethanol oxidation improved 13× under solar-simulated AM1.5G and 40× for surface plasmon resonance-targeted irradiation conditions after photodepositing Pd, consistent with enhanced participation of intraband-excited sp-band holes and desorption of ethanol oxidation reaction intermediates owing to photothermal effects.

Ethanol Oxidation via 12‐Electron Pathway on Spiky Au@AuPd Nanoparticles Assisted by Near‐Infrared Light

“…Then, holes would appear on the surfaces of active Pd sites. [81] Subsequently, the produced holes would oxidize the OH ads species (instead of OH − ions) adsorbed on the surfaces of Pd atoms into OH radicals, followed by the cleavage of the C-C bond of neighboring ethanol molecules absorbed on the surfaces of Pd atoms by reacting with OH radicals because of its extremely strong oxidative ability. [82,83] Moreover, partial electrons transferring from Pd to Au atoms and continuous consumption of holes can in turn effectively inhibit the recombination of hot electrons and holes.…”

Effect of Light Irradiation on Hot Electron-Mediated Photoreduction of Silver Ions on Single Gold Nanorods without a Reducing Agent

“…Among the several mechanisms that have been reported so far for photochemical reactions, mechanisms involving energetic hot carriers (electrons and holes) generated in Au nanoparticles upon LSPR excitation have attracted special research attention in recent years. − The growth rate or morphological selectivity of bimetallic structures through plasmonic-mediated synthesis has been reported, , and studies on the deposition growth of Pd and Pt by hot electron contribution have also been reported. , In addition, the growth of Au and Cu nanoparticles by SPR-based localized photothermal heating on Ag surfaces has been reported. , A mechanism in which the growth and etching of Au nanoparticles via plasmonic hot carriers is dependent on the light intensity and the concentration of HAuCl 4 has also been reported by Long et al Mukherjee et al reported that the transfer of hot electrons generated in Au nanoparticles to a H 2 molecule adsorbed on the nanoparticle surface triggered the dissociation of H 2 at room temperature . Furthermore, Kamarudheen et al reported a photoreduction mechanism based on interband charge carriers for the formation of Au@Ag core–shell structures .…”

Examining Silver Deposition Pathways onto Gold Nanorods with Liquid-Phase Transmission Electron Microscopy

“…The longitudinal LSPR is particularly sensitive to the AuNR aspect ratio, enabling tuning of the resonance across the visible and near-infrared . A secondary metal shell on the AuNR also impacts the LSPR response; coating AuNRs with silver (Ag) enhances their optical response and molecular detection sensitivity. , Other than Ag, deposition of catalytically active metals such as platinum (Pt) or palladium (Pd) onto AuNRs forms highly active photocatalysts. ,− AuNRs with Pt deposited specifically on the tips have demonstrated increased activity for the hydrogen evolution reaction compared to homogeneously Pt-covered AuNRs and other Au- and/or Pt-based nanostructures. , …”

“…23 laser irradiation power, and substrate coupling. 11,22,24,25 However, due to the diffraction-limited spatial resolution, DFS and other optical microscopy-based techniques cannot visualize detailed structural changes to an individual AuNR. An alternative and complementary approach is liquid-phase transmission electron microscopy (LP-TEM), which can visualize in real time metal shell deposition on nanoparticles with nanometer spatial resolution.…”

“…Using single-particle dark-field scattering (DFS) spectroscopy, Foerster et al related the extent of AuNR plasmon decay via chemical interface damping to ligand coverage density and AuNR size . DFS can also elucidate how plasmon energy transfer processes respond to other aspects of the local environment such as secondary metal decoration, laser irradiation power, and substrate coupling. ,,, However, due to the diffraction-limited spatial resolution, DFS and other optical microscopy-based techniques cannot visualize detailed structural changes to an individual AuNR. An alternative and complementary approach is liquid-phase transmission electron microscopy (LP-TEM), which can visualize in real time metal shell deposition on nanoparticles with nanometer spatial resolution. , In LP-TEM the electron beam interacts with water to produce reactive radicals capable of reducing metal ions into metal nanoparticles or oxidizing metal surfaces in situ. − Accordingly, the beam-induced chemistry present in LP-TEM has been harnessed to explore factors mediating formation and etching dynamics of nanocrystals featuring one or multiple metals. − Furthermore, Sutter et al proposed that the electron beam acts as an evanescent white light to stimulate LSPR in Ag nanoparticles, driving their growth and shape transformation during LP-TEM. , However, the relative contributions of radiolysis and plasmonic excitation on the deposition of a second metal onto plasmonic AuNRs during LP-TEM have not been established.…”