Thermal and Nonthermal Effects in Plasmon‐Mediated Electrochemistry at Nanostructured Ag Electrodes

Abstract

Hot carriers (HCs) and thermal effects, stemming from plasmon decays, are crucial for most plasmonic applications. However, quantifying these two effects remains extremely challenging due to the experimental difficulty in accurately measuring the temperature at reaction sites. Herein, we provide a novel strategy to disentangle HCs from photothermal effects based on the different traits of heat dissipation (long range) and HCs transport (short range), and quantitatively uncover the dominant and potential-dependent role of photothermal effect by investigating the rapid-and slow-response currents in plasmon-mediated electrochemistry at nanostructured Ag electrode. Furthermore, the plasmoelectric surface potential is found to contribute to the rapid-response currents, which is absent in the previous studies.Mostplasmonicapplications,suchasphotothermaltherapy, photodetection, and plasmon-mediated chemical reactions (PMCRs), are closely associated with the nonradiative decays of plasmons where hot carriers (HCs, electrons well above and holes well below the Fermi level of metals) are generated (HC effect) and the local heating is induced (thermal effect). [1] To quantify these two effects is of paramount importance for designing and optimizing energy-efficient plasmonic devices. Recently, several attempts have been made for distinguishing these effects, giving conflicting conclusions. [2] In these studies, thermal effect was first identified by virtue of the temperature change recorded using a thermal camera, and the contribution of HCs was then deduced by subtracting the thermal effect from the overall plasmonic effects. Unfortunately, the accurate measurement of the surface temperature at the reaction sites remains an exceptionally difficulty task for current techniques, and even a small error may result in a completely different conclusion because the reaction rates are exponentially dependent on temperature. [3] Herein, to bypass this difficulty, the HCs and thermal contributions in plasmon-mediated electrochemistry at nanostructured Ag electrode were decoupled and quantified based on its photoelectrochemical behaviors, taking advantage of the very different transport distances of phonons and HCs as well as the high temporal resolution in photoelectrochemical measurement. The dominant and potential-dependent role of thermal effect were readily revealed by differentiating the rapid-(I RC , non-thermal effect) and slow-(I SC , thermal effect) response currents in their photocurrent profiles. In essence, the nonthermal processes were found to originate from populating O 2 antibonding orbital by hot electron under cathodic biases, or from the "plasmoelectric effects" under anodic biases. Furthermore, the ratio between I SC and I RC can be manipulated by adjusting the electrode potential, laser wavelength and intensity, pointing to a promising route to control the thermal and nonthermal contributions to PMCRs for achieving optimal reaction selectivity and yields.The plasmonic Ag electrodes that feature a surface consist...

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] .…”

Plasmonic metal nanostructures: concepts, challenges and opportunities in photo-mediated chemical transformations

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Figure 5 The method that is not based on temperature measurement to disentangle thermal from nonthermal contributions (A and B) The variation of reaction rate as a function of the measurement errors of temperature, ΔT , at various activation energy barriers, ε a , (A) and real temperature, T r (B). (C) Schematic illustration of disentangling nonthermal and thermal effects in electrochemical reaction proceeding at nanostructured Ag electrode by illuminating at different locations ( Ou et al., 2020 ). (D) Rapid-response current ( I RC , nonthermal effects), slow-response current ( I SC , thermal effects), total photocurrent ( I total , total effects), and the ratio of I RC to I SC at different electrode voltages with laser switched on-off ( Ou et al., 2020 ).

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“… (C) Schematic illustration of disentangling nonthermal and thermal effects in electrochemical reaction proceeding at nanostructured Ag electrode by illuminating at different locations ( Ou et al., 2020 ). (D) Rapid-response current ( I RC , nonthermal effects), slow-response current ( I SC , thermal effects), total photocurrent ( I total , total effects), and the ratio of I RC to I SC at different electrode voltages with laser switched on-off ( Ou et al., 2020 ). …”

“… (C) Schematic illustration of disentangling nonthermal and thermal effects in electrochemical reaction proceeding at nanostructured Ag electrode by illuminating at different locations ( Ou et al., 2020 ). …”

“… (D) Rapid-response current ( I RC , nonthermal effects), slow-response current ( I SC , thermal effects), total photocurrent ( I total , total effects), and the ratio of I RC to I SC at different electrode voltages with laser switched on-off ( Ou et al., 2020 ). …”