The Role of Heating in the Electrochemical Response of Plasmonic Nanostructures under Illumination

The role played by heating in the electrochemical behavior of plasmonic nanostructures under illumination was examined through a combination of theoretical modeling and experimental investigations. A theoretical treatment of heating in plasmonic electrochemical systems was developed, which treats heat flow from arrays of nanoparticles attached to an electrode as a heat source delocalized across the electrode-solution interface. Within this framework, simple analytical expressions for the temperature profile in the vicinity of illuminated electrodes are presented for a 1D model treating heat transfer via conduction. Results from more detailed finite element simulations treating heat transfer via both conduction and convection in realistic cell geometries are also provided. Both approaches predict significant increases in the mass transfer of dissolved redox species, which can readily explain the current enhancements observed with electrodes decorated with plasmonic nanostructures under illumination. These predictions were tested experimentally by employing conventional, millimeter-sized electrodes decorated with Au nanoparticles in potential step experiments under intermittent illumination. Experiments with both outer-sphere (ferrocene methanol) and inner-sphere (hydrazine) redox couples displayed significant current enhancements due to illumination, which agreed well with theoretical predictions. Experiments at individual nanoparticles were also carried out using probe-based techniques. These measurements displayed no significant effects due to heating, attributable to efficient heat transfer away from nanoparticles in this experimental geometry. Implications of these results on research into the effects of hot charge carriers in electrochemical experiments are discussed.