Revitalizing spherical Au@Pd nanoparticles with controlled surface-defect density as high performance electrocatalysts

Abstract

In this work, core–shell (CS) Au@Pd nanoparticles (NPs) with about one Pd atomic layer (named C_mS Au_x@Pd_1−x NPs, in which m is the size of the core, and is 6, 12, 19, 30, and 57 nm and x is the molar content of Au in the whole NP) were first synthesized by ascorbic acid reduction of Na₂PdCl₄ solution on Au-NP seeds of various amounts of surface defects in water at room temperature. To the best of our knowledge, the concept of “surface-defect density” and the calculation method are proposed for the first time in NP-based nanocatalysts. On the basis of electrocatalytic results, it is found that the specific activities of the as-prepared C_mS Au_x@Pd_1−x NPs are increased with increase in their surface-defect densities while their mass activities and electrochemically active surface areas (ECSAs) both exhibit “volcano-type” dependence with respect to their size in the absence of carbon supports. Moreover, C₁₉S Au_0.91@Pd_0.09 NPs with Vulcan carbon supports show an optimal electrocatalytic performance and a long-term high electrocatalytic activity for ethanol oxidation. Their ECSA value, mass activity and specific activity are 119.8 m² g⁻¹, 11.0 A mg_Pd⁻¹, and 9.3 mA cm⁻², respectively, which are about 4.8-fold, 36.7-fold, and 7.8-fold better than those (24.9 m² g⁻¹, 0.3 A mg_Pd⁻¹, and 1.2 mA cm⁻²) of commercial Pd/C catalysts, respectively. This work provides not only a direct correlation between defect-density and catalytic activity, but also design rules for metal NP electrocatalysts with superior electrocatalytic performance.