Electrochemical dechlorination promotes syngas production in N-heterocyclic carbene protected Au13 nanoclusters

Surface ligands play an important role in dictating the structure and catalytic properties of metal nanoclusters. Recently, a novel class of Au clusters protected by N-heterocyclic carbenes (NHCs) and halogens has been synthesized; however, the dynamic stability of the Au-NHCs/Au-halogen interface in real electrochemical environments as well as the influence of the ligand layer on the catalytic process remains obscure. Herein, we combined first-principles simulations with experiments to investigate the metal-ligand interface interaction of the classical [Au₁₃(NHC^Me)₉Cl₃]²⁺ cluster and its unique potential to promote electrocatalytic CO₂ reduction to syngas. Our simulations revealed the facile shedding of chlorine ligands from the surface of the Au₁₃ core upon electrochemical biasing, and the more negative the applied potential, the faster the kinetics of the Au-Cl bond cleavage. By contrast, the Au-NHC interface is highly stable, indicating the greater stability of Au-C bonds over the Au-Cl bonds under electrochemical conditions. Interestingly, the exposed icosahedral Au in dechlorinated [Au₁₃(NHC^Me)₉Cl₂]³⁺ cluster is capable of efficiently catalyzing electrochemical CO₂ reduction to generate CO and H₂ with comparable barriers in a wide potential range, showcasing its strong potential for syngas formation. Our predictions are further corroborated by experimental electrochemical data, where X-ray photoelectron spectroscopy (XPS) verified halogen stripping under acid or neutral media, and the activated Au₁₃ cluster demonstrated enhanced catalytic efficacy for syngas formation with a CO : H₂ ratio of approximately 0.8 to 1.2 across a broad potential range of -0.50 to -1.20 V. This work reveals an exciting frontier in the understanding of ligand etching dynamics in NHC-protected metal nanoclusters, and particularly, the catalytic preference for syngas production is revealed for the first time in gold-based nanoclusters, which is distinctive from previously reported Au nanoclusters that mainly produce CO.