Branched Pd and Pd-based trimetallic nanocrystals with highly open structures for methanol electrooxidation

Branched monometallic and alloy nanostructures have been recognized as promising electrocatalysts, yet there are few protocols for the integration of their composition and architecture to advance their electrocatalytic performance and fewer studies relating the formation of new electronic states to their catalytic activities. Herein, a versatile, robust method has been developed for a high-yield synthesis of branched Pd and Pd-based trimetallic nanocrystals (NCs) with long, thin branches and open structures. Notably, the as-prepared branched Pd NCs can be effectively used as the core template to synthesize a novel class of branched Pd core–alloy shell trimetallic NCs, such as Pd@PtCu with varied atomic ratios of Pt to Cu and Pd@AuCu core@shell NCs. Such trimetallic core–shell NCs provide a new platform for developing high-performance electrocatalysts as a result of the combination of the open branched structure and modifying composition. Much enhanced activities toward methanol electrooxidation are observed on the branched Pd, Pd@AuCu, and Pd@PtCu NCs compared to the commercial Pt/C and PtRu/C catalysts and found to be strongly dependent on the structure and composition of the branched NCs. Particularly, among the branched Pd@PtCu with different shell compositions, Pd@AuCu, Pd@Pt, and Pd NCs, the branched Pd@Pt72Cu28 NCs show superior electrocatalytic performance largely due to the modification of the overall electronic properties caused by the formation of new electronic states in the presence of the Pt72Cu28 shell. This proposal is evidenced by the variations in the valence band structures.