Impact of Plasmonic Photothermal Effects on the Reactivity of Au Nanoparticle Modified Graphene Electrodes Visualized Using Scanning Electrochemical Microscopy

Atomically thin graphene electrodes enable the modulation of interfacial reactivity by means of underlying substrate effects. Here we show that plasmonic excitation of microscopic arrays composed of 50 nm Au nanoparticles situated underneath a graphene interface results in localized enhancements on the electrochemical readout. We used scanning electrochemical microscopy (SECM) in the feedback and H₂O₂ collection modes to identify the role of the generated plasmons on the electrochemical response. Using electrochemical imaging, supported by finite-element method simulations, we confirmed that a temperature rise of up to ∼30 K was responsible for current enhancements observed for mass transfer- limited reactions. On single-layer graphene (SLG) we observed a shift in the onset of H₂O₂ generation which we traced back to photothermal induced kinetic changes, raising k^o′ from 1.1 × 10^-8 m/s to 2.2 × 10^-7 m/s. Thicker 10-layer graphene electrodes displayed only a small kinetic difference with respect to SLG, suggesting that photothermal processes, in contrast to hot carriers, are the main contributor to the observed changes in interfacial reactivity upon illumination. SECM is demonstrated to be a powerful technique for elucidating thermal contributions to reactive enhancements, and presents a convenient platform for studying sublayer and temperature-dependent phenomena over individual sites on electrodes.