Light-Off in Plasmon-Mediated Photocatalysis.

Anders Hellman,Christoph Langhammer,Zafer Say,Sara Nilsson,Joachim Fritzsche,Astrid Boje,Henrik Ström,Christopher Tiburski

doi:10.1021/acsnano.1c01537

Anders Hellman, Christoph Langhammer + Show 6 more

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https://doi.org/10.1021/acsnano.1c01537

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Journal: ACS nano	Publication Date: Jun 22, 2021
Citations: 14	License type: CC BY 4.0

Affiliation: Chalmers University of Technology

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 Au50Pd50 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.

Highlights

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
We have shown that the photothermal reaction rate enhancement on nanofabricated Pd and Au50Pd50 alloy model catalysts during the catalytic oxidation of carbon monoxide (CO) strongly depends on the catalyst temperature in the dark, and is solely mediated by its light-off curve
We have found that the photothermal rate enhancement for the Pd system varies over 3 orders of magnitude at constant irradiance, depending on the position of the catalyst on the light-off curve

Summary

Introduction

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. We demonstrate using the example of CO oxidation over nanofabricated neat Pd and Au50Pd50 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. Temperature gradients may form due to (i) nonuniform metal nanoparticle distributions, (ii) inhomogeneous illumination intensity, (iii) 3D nano- or mesoporous support materials with complex and anisotropic heat transport properties, and (iv) attenuation/absorption of irradiated photons inside such a support material. These effects have been identified as important and pinpointed as inadequately addressed in the literature.[14,18]. The main reason for this ambiguity is that in corresponding studies only limited ranges of photon flux variation have been used since implementing the required several orders of magnitude difference in photon flux would require the use of very high-power light sources and/or the use of ultrasensitive detection techniques at very low reaction rates

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