Eppur Si Riscalda - and yet, It (Just) Heats Up: Further Comments on “Quantifying Hot Carrier and Thermal Contributions in Plasmonic Photocatalysis”

Abstract

Our Comment [1] (as well as Ref. [2], and the supporting theoretical studies [3, 4]) on recent attempts to distinguish thermal and non-thermal ("hot carrier") contributions to plasmon-assisted photocatalysis [5] initiated a re-evaluation process of previous literature on the topic within the nano-plasmonics and chemistry communities. The Response of Zhou et al. [6] attempts to defend the claims of the original paper [5].In this manuscript, we show that the Response [6] presents additional data that further validates our central criticism: inaccurately measured temperatures (that are lower than the actual temperature of the catalyst) led Zhou et al. to incorrectly claim conclusive evidence of non-thermal effects. We identify flaws in the experimental setup (e.g. the use of the default settings for the thermal camera and incorrect positioning of the thermometer) that may have led Zhou et al. to make such claims. We further show that the Response contains several factual errors and does not address the technical problems we identified with the data acquisition in [5]. We demonstrate that both the Response [6] and the original paper [5] contain additional faults, for example, in the power determination and in the normalization of the rate to the catalyst volume, and exhibit misconceptions regarding the thermo-optic response of metal nanostructures. The burden of proof required by the proposal of a novel physical mechanism has simply not been met, especially when the existing data can be modeled exquisitely by conventional theory.

Simple experimental procedures to distinguish photothermal from hot-carrier processes in plasmonics

“…In the case of a photochemical process in plasmonics, such as near-field enhancement of photochemical reactions or hot-charge-carrier-assisted redox reactions at the nanoparticle surface, the rate η 92 , 2016 93 , 2017 26,94 , 2018 23,24,41,42,56,84,95 , 2019 22,23,27,38,[48][49][50][96][97][98][99] , 2020 [100][101][102][103] photons and therefore to the incident light power impinging on the sample. This assumption holds true for CW illumination under moderate light power and may deviate toward a super-linear dependence for very high power 31 or under fs-pulsed laser illumination due to multiphoton absorption [32][33][34][35] .…”

“…However, as black body radiation depends not only on the temperature but also on the emissivity of the material, proper calibration of the reactive medium is critical for reliable measurements. The non-reliable determination of the sample's emissivity has already been put forward as a possible source of errors in hot-carrier-assisted plasmonic chemistry 41,[48][49][50] . In any case, one should avoid relying solely on a theoretical estimate of the emissivity based on the nature of the mixed materials covering the surface.…”