Light-Off in Plasmon-Mediated Photocatalysis

Abstract

In plasmon-mediated photocatalysis it is of critical importance to differentiate light-induced catalytic reaction rate enhancement channels, which include near-field effects, direct hot carrier injection, and photothermal catalyst heating. In particular, the discrimination of photothermal and hot electron channels is experimentally challenging, and their role is under keen debate. Here we demonstrate using the example of CO oxidation over nanofabricated neat Pd and Au 50 Pd 50 alloy catalysts, how photothermal rate enhancement differs by up to 3 orders of magnitude for the same photon flux, and how this effect is controlled solely by the position of catalyst operation along the light-off curve measured in the dark. This highlights that small fluctuations in reactor temperature or temperature gradients across a sample may dramatically impact global and local photothermal rate enhancement, respectively, and thus control both the balance between different rate enhancement mechanisms and the way strategies to efficiently distinguish between them should be devised.

Optical Hydrogen Nanothermometry of Plasmonic Nanoparticles under Illumination

“… 15 − 17 At the same time, it is well known that LSPR excitation leads to significant light absorption, which via coupling to lattice phonons increases nanoparticle temperature, 18 − 20 and that such a temperature increase may have both wanted 21 − 23 and unwanted 24 consequences for specific applications. One such area where the potential impact of plasmon-induced optical heating of nanoparticles is highly debated 25 − 30 and potentially very significant 31 is plasmon-mediated catalysis. In this field, several different reaction enhancement mechanisms have been proposed, 31 − 34 and it remains a great challenge to distinguish between photothermal- and hot carrier-induced reaction enhancement.…”

“…Metal nanoparticles have found application in a wide range of fields owing to their support of localized surface plasmon resonances (LSPRs). , All these applications have in common that they rely on the irradiation of light to unlock plasmonic functions utilized, for example, for optical sensing, , treatment of disease, , photovoltaic devices, , optical metamaterials, − dynamic coloring, , and active plasmonics and to enhance catalytic reactions. − At the same time, it is well known that LSPR excitation leads to significant light absorption, which via coupling to lattice phonons increases nanoparticle temperature, − and that such a temperature increase may have both wanted − and unwanted consequences for specific applications. One such area where the potential impact of plasmon-induced optical heating of nanoparticles is highly debated − and potentially very significant is plasmon-mediated catalysis. In this field, several different reaction enhancement mechanisms have been proposed, − and it remains a great challenge to distinguish between photothermal- and hot carrier-induced reaction enhancement .…”

“…One such area where the potential impact of plasmon-induced optical heating of nanoparticles is highly debated − and potentially very significant is plasmon-mediated catalysis. In this field, several different reaction enhancement mechanisms have been proposed, − and it remains a great challenge to distinguish between photothermal- and hot carrier-induced reaction enhancement . One reason is that commonly conducted experiments to disentangle these mechanisms rely on probing the catalytic activity as a function of photon flux.…”

Challenges and Opportunities for Renewable Ammonia Production via Plasmon‐Assisted Photocatalysis

“…[ 98 ] In general, photoheating is an unavoidable phenomenon when working with plasmonic systems, and it is in general important to take its effect into account, as it can noticeably change the dynamics when using temperature‐sensitive photocatalysts. [ 116 ]…”

Distinguishing Thermal from Nonthermal (“Hot”) Carriers in Illuminated Molecular Junctions

“…However, the practical separation between thermal and nonthermal carriers is very challenging, because the number of the high-excess-energy nonthermal electrons is many orders of magnitude smaller than the number of thermal (i.e., low excess energy) carriers. Thus, the various attempts made to directly quantify the contributions of these two types of charge carriers (e.g., to chemical reaction rates in the context of plasmon-assisted photocatalysis) frequently fail, − because the control thermocatalysis (light off) experiments must reproduce exactly the temperature profile of the photocatalysis (light on) experiments, , a task which is nearly impossible (although progress has been made in this direction). − …”