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, Au^δ+ 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 Au₂₅^q nanoclusters with different ground state charges (q = −1, 0, +1) to study the role of charged active sites in Au-catalyzed electrochemical reactions. Au₂₅^q 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 Au₂₅^q 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. Au₂₅^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.