Tuning the Fermi Level of Silver Nanoparticles by Thiocyanate Ions for Plasmonic Catalysis

The Fermi level of plasmonic metals governs the generation and energetics of hot electrons, thereby determining their catalytic behavior. Herein, we introduce thiocyanate ions (SCN^-) as surface ligands to modulate the Fermi level of silver. Their strong and stable chemisorption enables efficient tuning of the electronic structure over a broad range. Utilizing <i>in situ</i> surface-enhanced Raman spectroscopy, we systematically investigate how Fermi level elevation influences hot electron dynamics in plasmonic catalysis in both carrier population and energy distribution. Through representative model reactions, including nitro group reduction and C-Cl bond cleavage, we demonstrate that the Fermi level upshift allows precise control over reaction selectivity and enables transformations that are otherwise inaccessible under standard conditions. These findings establish ligand-based Fermi level engineering as a powerful and generalizable strategy for mechanistic investigations and the rational design of plasmonic catalysts.