Probing active site chemistry with differently charged Au-25(q) nanoclusters (q = -1, 0, +1)

Charged active sites are hypothesized to participate in heterogeneously-catalyzed reactions. For example, Au delta+ 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 Au-25(q) nanoclusters with different ground state charges (q = -1, 0, +1) to study the role of charged active sites in Au-catalyzed electrochemical reactions. Au-25(q) clusters showed charge state-dependent electrocatalytic activity for CO2 reduction, CO oxidation and O-2 reduction reactions in aqueous media. Experimental studies and density functional theory identified a relationship between the Au-25(q) charge state, the stability of adsorbed reactants or products, and the catalytic reaction rate. Anionic Au-25(-) promoted CO2 reduction by stabilizing coadsorbed CO2 and H+ reactants. Cationic Au-25(+) promoted CO oxidation by stabilizing coadsorbed CO and OH- reactants. Finally, stronger product adsorption at Au-25(+) inhibited O-2 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. Au-25(q) 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.