Correlation of Surface Ag Content in AgPd Shells of Ultrasmall Core–Shell Au@AgPd Nanoparticles with Enhanced Electrocatalytic Performance for Ethanol Oxidation

We report the synthesis of well-dispersed, ultrasmall, core–shell (CS) Au@AgPd nanoparticles (NPs) via galvanic reaction of Ag shells of CS Au@Ag NPs with Pd 2+ ions at room temperature. It is found that Ag content in the resulting AgPd shells is dependent mainly on the thickness of the original Ag shells and the concentrations of Pd 2+ ions used for the galvanic reaction. In addition, the electrocatalytic performance of the resulting CS Au@AgPd NPs is dependent on the surface Ag content (s-Ag n Pd 1– n ) in the AgPd shells (where s-Ag n Pd 1– n is added to highlight the surface Ag content) while being independent of the total Ag content. When the ultrathin AgPd shells with 0.79 nm thickness and the surface Ag content of about 29.4% are formed on ca. CS 0.60 Au@Ag NPs, the resulting CS 0.60 Au@AgPd-s-Ag 0.294 Pd 0.706 NPs with average size of 8.5 nm have significantly increased electrochemically active surface area (up to 77.5 m 2 g –1 ) and exhibit superior catalytic activity (1.16 A mg Pd –1 ) toward ethanol oxidation (0.50 M) in alkaline media (0.30 M KOH), about 5 times higher than that of commercial Pd/C catalyst (0.20 A mg Pd –1 ).