The photoelectric effect at the metal-solution interface leads to the creation of solvated electrons, which are powerful reducing agents that enable new transformations for photo-electrochemical catalysis. Previous work indicates that nanostructured electrodes exhibit increased photoemission efficiencies when illuminated near the plasmon resonance. However, while the effects of plasmon excitation on electron emission into vacuum, semiconductors, and molecules have recently become major points of interest, the mechanism of plasmon-induced electron transfer into liquids has remained unclear. In this work, we measure photocurrents from smooth and nanostructured gold and silver electrodes to quantify the effect of plasmon excitation on electron photoemission into water. Above the photoemission threshold of 2.7 eV, photoemission yields followed the electric field enhancement for nanostructured silver electrodes with a peak enhancement of 10. Gold electrodes exhibited no plasmonic enhancement due to interband transitions. Together, these results reveal that plasmon-induced photoemission proceeds via an indirect mechanism, where energetic carriers are first generated within the nanoparticle through plasmon decay. Hot electrons that reach the metal-solution interface with energies of at least 2.7 eV relative to the Fermi level of the metal can then inject into the solution and become solvated. Solvated electron yields can thus be maximized by designing nanoparticle electrodes that produce a high number of hot electrons with energies above 2.7 eV.

Photoemission of plasmonic hot electrons into solution

ACS Spring 2022

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