Probing active site chemistry with differently charged Au25q nanoclusters (q = −1, 0, +1)

Abstract

Charged active sites are hypothesized to participate in heterogeneously-catalyzed reactions. For example, Auδ+ species at the catalyst surface or catalyst–support interface are thought to promote the thermally-driven CO oxidation reaction. However, the concept of charged active sites is rarely extended to electrochemical systems. We used atomically precise Au25q nanoclusters with different ground state charges (q = −1, 0, +1) to study the role of charged active sites in Au-catalyzed electrochemical reactions. Au25q clusters showed charge state-dependent electrocatalytic activity for CO2 reduction, CO oxidation and O2 reduction reactions in aqueous media. Experimental studies and density functional theory identified a relationship between the Au25q charge state, the stability of adsorbed reactants or products, and the catalytic reaction rate. Anionic Au25− promoted CO2 reduction by stabilizing coadsorbed CO2 and H+ reactants. Cationic Au25+ promoted CO oxidation by stabilizing coadsorbed CO and OH− reactants. Finally, stronger product adsorption at Au25+ inhibited O2 reduction rates. The participation of H+ and OH− in numerous aqueous electrocatalytic reactions likely extends the concept of charge state-mediated reactivity to a wide range of applications, including fuel cells, water splitting, batteries, and sensors. Au25q clusters have also shown photocatalytic and more traditional thermocatalytic activity, and the concept of charge state-mediated reactivity may create new opportunities for tuning reactant, intermediate and product interactions in catalytic systems extending beyond the field of electrochemistry.