Unraveling the Photocatalytic Mechanism of N 2 Fixation on Single Ruthenium Sites.

Photocatalytic N 2 fixation offers promise for ammonia synthesis, yet traditional photocatalysts encounter challenges such as low efficiency and short carrier lifetimes. Atomically precise ligand-metal nanoclusters emerge as a solution to address these issues, but the photophysical mechanism remains elusive. Inspired by the synthesis of Au 4 Ru 2 NCs, we investigate the mechanism behind N 2 activation on Au 4 Ru 2 , focusing on photoactivity and carrier dynamics. Our results reveal that vibration of the Ru-N bond in the low-frequency domain suppresses the deactivation process leading to a long lifetime of the excited N 2 . By the strategy of isoelectronic substitution, we identify the single Ru sites as the active sites for N 2 activation. Furthermore, these ligand-protected M 4 Ru 2 (M = Au, Ag, Cu) NCs show robust thermal stability in explicit solvation and decent photochemical activity for N 2 activation and NH 3 production. These findings have significant implications for the optimization of catalysts for sustainable ammonia synthesis.