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

In this work, core-shell (CS) Au@Pd nanoparticles (NPs) with about one Pd atomic layer (named CmS Aux@Pd1-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 CmS Aux@Pd1-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 m(2) 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 m(2) 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.