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 have been synthesized, however, the dynamic stability of the Au-NHCs/Au-halogen interface in real electrochemical environments as well as the influence of ligand layer on the catalytic process remain obscure. Herein, we combined first-principles simulations with experiments to investigate the metal-ligand interface interaction of the classical [Au13(NHCMe)9Cl3]2+ cluster and its unique potential to promote electrocatalytic CO2 reduction to syngas. Our simulations revealed the facile shedding of chlorine ligand 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-NHCs interface is highly stable, indicating the stronger stability of Au-C bonds over the Au-Cl bond under electrochemical conditions. Interestingly, the exposed icosahedra Au in dechlorinated [Au13(NHCMe)9Cl2]3+ cluster is capable to efficiently catalyze electrochemical CO2 reduction to generate CO and H2 with comparable barrier 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 the halogen stripping under the 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 NHCs-protected metal nanoclusters, and particularly, the catalytic preference for syngas production is first revealed in gold-based nanoclusters, which is distinctive from previously reported Au nanoclusters that mainly produce CO.