(Invited) Time-Resolved in Situ Electrochemical SFG Study of Hot Electron Transfer from Metal Electrodes to Adsorbates

Abstract

here have been recent reports of light enhanced electrocatalysis on metal electrodes, including H2 generation and CO2 reduction. The mechanism of such process remains unclear. One possible mechanism is selective excitation of adsorbate vibrational modes by rapid hot electron transfer and back transfer between the metal and the adsorbate. Although this mechanism has been studied for adsorbate on metal surfaces under vacuum conditions, it is unclear whether similar processes occur under electrochemical conditions and can be tuned by electrochemical bias. Using time-resolved vibrational sum frequency generation (VSFG) spectroscopy, we directly measure hot electron induced vibrational dynamics of adsorbates on metal electrodes. For CO adsorbed on Au electrodes, we show that excitation of the metal leads to the generation of vibrationally excited CO molecules. Detailed analysis reveals that the formation and decay of the excited adsorbates follows the electronic temperature of the electron, indicating the direct coupling of adsorbate vibration modes with hot electrons in the electrodes, likely through ultrafast hot electron transfer and back transfer induced vibrational excitation. This result suggests the possibility of plasmon (or light)-enhanced electrochemistry on metal electrodes. Ongoing studies are systematically examining how the hot electron transfer process depends on the nature of the electrode and applied bias.