Hot carrier multiplication in plasmonic photocatalysis

Abstract

Light-induced hot carriers derived from the surface plasmons of metal nanostructures have been shown to be highly promising agents for photocatalysis. While both nonthermal and thermalized hot carriers can potentially contribute to this process, their specific role in any given chemical reaction has generally not been identified. Here, we report the observation that the H2–D2 exchange reaction photocatalyzed by Cu nanoparticles is driven primarily by thermalized hot carriers. The external quantum yield shows an intriguing S-shaped intensity dependence and exceeds 100% for high light intensities, suggesting that hot carrier multiplication plays a role. A simplified model for the quantum yield of thermalized hot carriers reproduces the observed kinetic features of the reaction, validating our hypothesis of a thermalized hot carrier mechanism. A quantum mechanical study reveals that vibrational excitations of the surface Cu–H bond is the likely activation mechanism, further supporting the effectiveness of low-energy thermalized hot carriers in photocatalyzing this reaction.

Plasmonic catalysis with designer nanoparticles

“…17,24–29 Therefore, plasmonic NPs have been attracting strong interest due to their ability to accelerate and control molecular transformations due to the LSPR excitation under milder conditions relative to traditional catalysis based on external heating. 30–34 This field enables, at least in principle, to combine optical and catalytic properties at the nanoscale as well as to use VIS or near-IR light as a sustainable and abundant energy input to drive and control molecular transformations. 18,26,35 Importantly, plasmonic catalysis allows one to overcome some of the intrinsic limitations of conventional wide bandgap semiconductor photocatalysts.…”

“…16 In fact, plasmonic NPs are currently at the forefront of enhancing photocatalytic efficiencies. 18,29,31,32,36,37 While plasmonic NPs have been extensively employed as sensitizers in conjunction with semiconductor photocatalysts, it is important to clarify that this is not the focus of this feature article. 38–41…”

Morphology and Optical Properties of Gas-Phase-Synthesized Plasmonic Nanoparticles: Cu and Cu/MgO

“…On the other hand, Cu NPs can present some advantages, because of the low cost and versatility of the raw material. Indeed, researchers have turned their attention to gas-phase-synthesized Cu NPs for their interesting properties [32][33][34][35][36]. Cu NPs have been used for applications in photocatalysis, for instance, in H 2 -D 2 exchange reaction, driven primarily by thermalized hot carriers [34], and to improve the performances of perovskite light-emitting diodes [35].…”

“…Indeed, researchers have turned their attention to gas-phase-synthesized Cu NPs for their interesting properties [32][33][34][35][36]. Cu NPs have been used for applications in photocatalysis, for instance, in H 2 -D 2 exchange reaction, driven primarily by thermalized hot carriers [34], and to improve the performances of perovskite light-emitting diodes [35]. The main problem with the use of Cu NPs is their instability during air exposure, with consequent oxidation and loss of the localized surface plasmon resonance (LSPR).…”

“…Ag/MgO NPs produced in this way were also deposited on the porous TiO 2 layer of perovskite solar cells, giving rise to an increase in PCE by 5% [15]. Although Cu NPs/MgO systems have been previously studied, MgO has mainly been used as an inert substrate [3,21,34,35] In this study, Cu NPs and Cu/MgO NPs were generated with a magnetron-assisted gas aggregation source (GAS), and they were co-deposited with MgO by making use of reactive thermal evaporation of Mg in O 2 . The chosen substrates were Si with its native oxide (Si/SiO x ), highly oriented pyrolytic graphite (HOPG), and quartz.…”