Figure 1: Schematic representation of the
plasmon-enhanced CO
2
methanation process.
1. Pre-reading
The ever-accelerating pace of industrialization has led to an increase in
concentration of carbon dioxide (CO
2
), causing concerns about
climate change and its consequences. This demands innovative methods to capture
and convert CO
2
. By leveraging nanoscale light-matter interactions,
plasmonic photocatalysis has emerged as a promising strategy to harness solar
energy and selectively drive CO
2
conversion into value-added
products.
The strong and confined
optical near-fields, along with energetic hot carriers and localized thermal
contributions, offer an opportunity to steer chemical reaction pathways. Yet,
the intricate and collaborative interplay of these mechanisms has sparked a
debate regarding their respective impacts, which raised questions about the significance
of plasmonic resonances in driving selective photocatalysis. In recent years
the relative contributions of these processes have been assessed using advances
in computational quantum physics and remarkable experimental demonstrations .
As a result, the significance of nonthermal effects (optical near-fields and
hot carriers) has been unveiled, effectively boosting the field plasmonic
catalysis and facilitating achievements such generation of valuable
hydrocarbons through CO
2
photoreduction on plasmonic nanoparticles.
This Review provides a critical synthesis of
the state-of-the art strategies for driving efficient and selective plasmonic
CO
2
photosynthesis using plasmonic structures. Starting from the
fundamentals of plasmon photocatalysis, we discuss the seminal works that led
to the ongoing debate on the reaction mechanism, address recent experimental
advances on plasmon CO
2
photoreduction differentiating between
in-situ
and ensemble measurements, and offer our perspective on the development of the
field.
2. Background
Artificial
photosynthesis enables a closed-loop solution for producing hydrocarbons from
CO
2
and water using sunlight to drive the reaction. Leveraging the
exquisite control of light-matter interactions at the nanoscale afforded by
plasmonic nanostructures offers a prospective avenue for efficiently
facilitating chemical transformations. Recently, the use of plasmonic materials
as active elements has sparked renewed interest the field of plasmonics, thanks
to the demonstration of enhanced photochemical reaction and the promise of
achieving reaction selectivity, suggesting a strategy for sustainable chemical
production.
Upon light interaction, nanostructured metals exhibit strong light–matter
interactions, resulting in the excitation of localized surface plasmon
resonances (LSPRs). These provide a way to concentrate light in subwavelength
volumes resulting in highly enhanced electric fields strongly confined at the
nanostructure’s surface. Following their excitation, the non-radiatively decay
of the LSPRs generates a population of highly energetic electron-hole pairs,
commonly referred to as hot carriers. These photo-excited carriers gradually
lose their energy through scattering events and ultimately release it to the
environment as heat, resulting in a localized temperature increase. Enhanced
fields, hot carriers, and thermal gradient -either individually or
synergistically- can be harnessed to drive and promote chemical reactions, and
differentiating between them has opened scientific debates in the literature,
which will be addressed throughout the Review article.
