Hot Carriers versus Thermal Effects: Resolving the Enhancement Mechanisms for Plasmon-Mediated Photoelectrochemical Reactions

Abstract

Nonradiative decay of localized surface plasmons results in the production of hot charge carriers and the generation of heat, both of which can affect the efficiency of plasmon-mediated photoelectrochemical processes. Unfortunately, decoupling the impact of each effect on measured photocurrents is extremely challenging because the relative contribution of the two plasmon decay pathways cannot be controlled or easily measured. Here, we present a methodology for exploring the roles of hot carriers and heat generation on plasmon-mediated photoelectrochemical processes using scanning electrochemical microscopy (SECM). Light is used to drive a redox reaction at a plasmonic substrate, while an ultramicroelectrode tip is positioned close to the substrate to read out both the reaction products and the mass transfer rate of the redox species. By controlling the potential at the tip and substrate electrodes, the roles of photoinduced reactions at the substrate and enhanced mass transport to the tip due to local heating can be isolated and investigated independently. We observe enhanced photo-oxidation at the substrate that is due to both plasmon-generated hot holes as well as a thermal-induced change in the equilibrium potential of the redox molecules. The concentration of the reaction products changes as a function of excitation intensity, showing a linear dependence on hot carrier effects and an exponential dependence for thermal effects, and allowing us to quantify the relative contributions of the two plasmon decay pathways to enhanced photo-oxidation. This SECM approach is suitable for probing a variety of photoactive structures used in photovoltaic and photocatalytic devices.

Mechanistic Studies of Plasmon Chemistry on Metal Catalysts

“…Golubev et al concluded that local heating was crucial for plasmon-induced reduction from pNTP to pATP, which was investigated by multiwavelength and temperaturedependent SERS measurements. [58] They clarified that photooxidation was enhanced by the hot carriers and the local heating, thereby causing ap otential shift. [37] Yu et al used scanning electrochemical microscopy (SECM) to investigate the effects of both the hot carriers and local heating generated by the LSP on photoelectrochemical reactions.…”

“…[37] Yu et al used scanning electrochemical microscopy (SECM) to investigate the effects of both the hot carriers and local heating generated by the LSP on photoelectrochemical reactions. [58] They clarified that photooxidation was enhanced by the hot carriers and the local heating, thereby causing ap otential shift. In contrast to these studies,K eller and Frontiera reported that the local heating mechanism is not aprimary mechanism for most plasmon-induced chemical reactions,which was proven by ultrafast Raman thermometry.…”

Synergy between Plasmonic and Electrocatalytic Activation of Methanol Oxidation on Palladium–Silver Alloy Nanotubes

“…Although a cooling bath maintained the temperature of the bulk electrolyte at 30 °C, limits in the kinetics of heat removal can result in a spatial temperature profile, whereby the electrocatalyst/electrolyte interface may be at an elevated temperature. Consequently, the diffusion of reactive species and kinetics of electrochemical reactions at the interface may be enhanced by such photothermal heating, potentially resulting in the increase in activity upon visible‐light illumination.…”

Quantifying Photothermal and Hot Charge Carrier Effects in Plasmon-Driven Nanoparticle Syntheses

“…7 As such, quantifying the contributions of localized and collective plasmonic heating is crucial for properly understanding the activation mechanism of light-driven nanoparticle syntheses. 26 In the limit of low light scattering and no convection, empirical equations have been derived to correlate the local temperature increase ! !, to the collective increase in temperature of the irradiated volume of solution.…”