Size-dependent synthesis and catalytic activities of trimetallic PdAgCu mesoporous nanospheres in ethanol electrooxidation

Mesoporous noble metal nanocrystals have exhibited significant potential in electrocatalysis. However, it remains a big challenge to controllably synthesize sub-100 nm multimetallic mesoporous nanospheres (MNSs) with precisely tunable sizes and to further understand their size-dependent electrocatalytic performances. In this manuscript, a one-pot solution-phase strategy was developed for the formation of nanosized trimetallic PdAgCu MNSs with cylindrically open mesoporous nanochannels and continuous frameworks. The resultant Pd-based MNSs were precisely tailorable not only in terms of size (from 21 to 104 nm), but also in terms of elemental ratios and compositions (PdAgCu, PdAgPt, PdAgFe, PdPtCu, and PdCuRu). This system thus provided a facile yet straightforward means to evaluate the size effect of trimetallic MNSs in electrocatalysis. As an example, trimetallic PdAgCu MNSs with an average size of 36 nm exhibited the best activity of 4.64 A mg(Pd)(-1) in the electrocatalytic ethanol oxidation reaction, 1.1-1.7 fold higher than that of MNSs with smaller or larger sizes and 5.9 fold higher than that of commercial Pd black catalyst. By means of kinetic studies, the size-dependent electrocatalytic performance can be ascribed to the optimization and balance between electron transfer and mass transfer processes inside PdAgCu MNSs. We expect that the size effect of multimetallic MNS nanocatalysts presented here may provide a general synthetic methodology for rational design of sizedependent nanocatalysts for a broad range of applications.